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GemBuilder for Smalltalk User`s Guide

1. Client Object looked up in Smalltalk Y Y name1 name2 Biss ed up in como Senet E p gt Server Object GbsNameConnector Connecting by Identity Fast Connectors Name lookup in both client Smalltalk and GemStone Smalltalk can be slow if you are using a lot of connectors You can bypass the name lookup by using a fast connector which saves direct references to the client Smalltalk objects and the object IDs of the GemStone server objects that are connected Using fast connectors can be risky however If the GemStone server object is renamed or redefined a fast connector will continue to point to the old object the one with the same object identifier When the identity of an object changes for example if it is a variable that you assign to a new object a fast connector becomes incorrect An out of date fast connector may cause an object does not exist error or it may silently continue to pass messages to an old object Because using object identity is not always an appropriate way to resolve an object we recommend that you generally use standard connectors instead of fast connectors especially during early development stages You can always use the Connector Browser to change a connector type later when you are certain that your application can rely on named objects to have a constant identity March 2006 GemStone Systems Inc 6 9 Making a
2. 11 15 Appendix A Configuring GemBuilder GemBuilder Configuration Parameters A 1 Using Configuration Parameters to Tune Your Application A 3 The Settings Browser cl a ERR IE a A 8 Opening the Settings Browser o o A 8 The VisualWorks 7 x Settings Browser A 9 Parameter Categorization o o ee eee A 9 The VisualWorks 5i Settings Browser o o A 11 March 2006 GemStone Systems Inc xvil GemBuilder User Manual Appendix B Packaging Runtime Applications Bil Prerequisites 226 ak ee A BNA IR a B 1 Names h Adie 5228 dl hee At da att A B 1 Replicating Blocks o o o ooo ooo o en B 2 Defunct Stubs and Forwarders B 2 Shared Libraries 4 a oie Beka eS SB da B 2 B 2 Packaging css Glee ira mie wes esas B 2 Appendix C Network Resource String Syntax CP OV eRVICW v5 3 any lea eae BO ek ee Bs ide ee ees a D 1 C2 Defaults 2 Siok d 6k eres ee OSS EA E rt D 2 C3 Notation cee eA he a EG a Re BA EE ee SE D 3 CMO YI aX sic oat Ea te BR ee aa E Se oe Go aed a Bk Pek D 4 Appendix D Client Smalltalk and GemStone Smalltalk xvili GemStone Systems Inc March 2006 List of Figures Figure 1 1 The GemStone Object Server 2 0 ee ee 1 2 Figure 2 1 RPC and Linked Gem Processes 2 0 000000 0004 2 4 Figure 2 2 The GemStone Session Browser 2 0 0 ee ee ee 2 8 Figure
3. 11 4 GemStone Systems Inc March 2006 Performance Tuning Profiling Table 11 2 Session Main Statistics Statistic Description nbEndResultProgressed The number of times GciNbEnd was called and progress was made nbEndResultNoProgress The number of times GciNbEnd was called when the result wasn t ready and no progress was made gsObjectCacheSize The number of entries in this session s gsObjectCache To enable the main statistics without enabling cache statistics execute GBSM mainStatsEnabled true Unlike the all in one statsEnabled method this method doesn t start the statistics monitor To start the statistics monitor execute GBSM statMonitorRunning true To specify a specific statistics archiving interval in milliseconds execute GBSM statSampleInterval milliseconds Cache Inventory Statistics GBS provides cache inventory statistics which show the number of instances of and bytes consumed by each class of object found in the stObjectCache To enable cache inventory statistics without enabling main statistics execute GBSM cacheStatsEnabled true GBSM statMonitorRunning true Cache inventory statistics are more expensive to sample and archive than the main GBS statistics Because of this cache statistics are not sampled and archived every time the statistics monitor performs sampling and archiving of the main statistics By default the cache statistic
4. Network Resource String Syntax Syntax authorization modifier auth encrypted username password krb auth specifies a valid user on the target network A valid password is needed only if the resource type requires authentication encrypted is used by GemStone utilities If no authentication information is specified the system will try to get it from the netrc file This type of authorization is the default krb specifies that kerberos authentication is to be used instead of a user name and password username nrs identifier If no user name is specified the default is the current user See the earlier discussion of nrs identifier password nrs identifier If no password is specified the system will try to obtain it from the user s netrc file See the earlier discussion of nrs identifier environment modifier netldi dir log nrs identifier netldi causes the named NetLDI to be used to service the request If the nrs identifier is numeric the NetLDI that is listening on that port number is used If no NetLDI is specified the default is net 1di61 See the earlier discussion of nrs identifier dir sets the default directory of the network resource It has no effect if the resource already exists If a directory is not set the pattern H defined below is used See the earlier discussion of nrs identifier log sets the name of the log file of the network resource
5. GemBuilder User Manual latest technical information for GemStone products We also welcome suggestions and ideas for improving and expanding our site to better serve you You may need to contact Technical Support directly for the following reasons e Your technical question is not answered in the documentation e You receive an error message that directs you to contact GemStone Technical Support e You want to report a bug e You want to submit a feature request Questions concerning product availability pricing keyfiles or future features should be directed to your GemStone account manager When contacting GemStone Technical Support please be prepared to provide the following information e Your name company name and GemStone S license number e The GemStone product and version you are using e The hardware platform and operating system you are using e A description of the problem or request e Exact error message s received if any Your GemStone support agreement may identify specific individuals who are responsible for submitting all support requests to GemStone If so please submit your information through those individuals All responses will be sent to authorized contacts only For non emergency requests the support website is the preferred way to contact Technical Support Only designated support contacts may submit help requests via the support website If you are a designated support contact for your company
6. March 2006 GemStone Systems Inc 2 9 Logging In To and Logging Out Of GemStone GemBuilder User Manual 2 5 Logging In To and Logging Out Of GemStone Before you can start a GemStone session you need to have a Stone process and for an RPC session a NetLDI network long distance information process running See your System Administrator if the transcript indicates that these processes aren t active Depending on the terms of your GemStone license you can have many sessions logged in at once from the same GemBuilder client These sessions can all be attached to the same GemStone repository or they can be attached to different repositories Logging In To GemStone Programmatically The protocol for logging in is understood both by GBSM and by instances of GbsSessionParameters To log in using a specific session parameters object send a login message to the parameters object itself mySession aGbsSessionParameters login To start multiple sessions with the same parameters simply repeat these login messages An application can also send a generic login message to GBSM mySession GBSM login This message invokes an interactive utility that allows you to select among known GbsSessionParameters or to create a new session parameters object using the Session Parameters Editor A successful login returns a unique instance of GbsSession An unsuccessful login attempt returns nil Each instance of GbsSession mainta
7. Forwarders them to its associated client Smalltalk object where state resides and behavior is implemented You can create forwarders in several ways Create a connector with a postconnect action of forwarder or clientForwarder For example connect the server global variable BigDictionary as a forwarder to the server so that it isn t replicated in the client Specify that a given instance variable must always appear on the client as a forwarder to the server using a replication specification discussed starting on page 5 21 For example a client class might implement a specification that declares the instance variable inventory as a forwarder to the server Prefix fw to a method name to return a forwarder from any message send to the server For example to return a forwarder from a GemStone server name lookup send the GbsSession fwat or fwat ifAbsent instead of at or at ifAbsent Override all these by implementing a class method instancesAreForwarders to return true and all instances of that class and its subclasses will be forwarders to the server Subclasses of GbsServerClass already respond true to this message GbsServerClass is an abstract class and all instances that inherit from it become forwarders to the server When sent to a class that inherits from GbsServerClass the instance creation methods new and new create a new instance of the class on the server and return a forwarder to that instance Sending
8. Profiling GemBuilder User Manual Table 11 2 Session Main Statistics Statistic Description objectsTraversed The total number of objects with or without a value buffer received by traversal call bytesTraversed The cumulative number of bytes returned by traversal calls traversalUnpackingTime The total number of milliseconds spent unpacking traversal buffers storeTraversals The number of store traversal calls made bytesSentByStoreTraversal The number of bytes sent cumulatively by store traversal calls objectsStoredBy Traversal The total number of objects stored by store traversal calls sigAborts The number of signaled aborts received lostOtRoots The number of lostOTRoot signals received changedObjNotifications The number of changed object notifications received sessionSignals The number of gem to gem signals received freeOopsFetched The number of free oops fetched sessionProtectinvocations The number of times the sessionProtect semaphore has been invoked cinterfaceProtectinvocations The number of times this session s cInterface accessProtect semaphore has been invoked clnterfaceProtectTime The amount of time spent in the session s clnterface accessProtect critical region gciErrors The number of errors reported by GciErr nbEndResultReady The number of times GciNbEnd was called and a result was ready
9. category method classmethod method classmethod printit commit removeAll 1Methods doit removeAl1lClassMethods The GemStone file in mechanism acknowledges the presence of the following commands by adding notes to the System Transcript but it does not execute them display omit expectvalue output level remark limit status list time If GemBuilder encounters any other Topaz commands it stops reading the file and displays an error notifier The file in mechanism does not display execution results either Instead it appends information to the System Transcript about the files it reads and the classes and categories for which it compiles methods Handling Errors While Filing In If one of the modules run commands or method definitions that you re filing in contains a GemStone Smalltalk syntax error GemStone displays a compilation error notifier that contains the erroneous module in a text editor If you correct the error and then choose Save GemStone recompiles the module and then processes the rest of the file In the case of authorization problems commands that the file in mechanism doesn t recognize or other errors GemStone displays a simple error notifier without an editor and stops processing the file 3 20 GemStone Systems Inc March 2006 Chapter Debugging In addition to the basic code development tools described in the previous chapter GemStone also provides GemStone
10. ooo e a 6 7 Connection Ordets asd ane giie i BA ee ee 6 8 HOOKUP auth tc ox Eta shat IN els Ue tank dl bd le dede Ugh a 6 8 Connecting by Identity Fast Connectors 6 9 6 4 Making and Managing Connectors 2 20 0 a 6 10 Making Connectors Programmatically 6 10 Creating Connectors o o o ee eee 6 11 Setting the Postconnect Action 000 6 11 Adding Connectors to a Connector List 6 12 Session Control o 6 13 The Connector Browser e a 6 16 Th Group Pan n coi a a PA et eed 6 17 The Connector Pane 0 0 ee 6 17 The Control Panel 0 0 i ore aa e A a aR Ia at 6 17 Postconnect Action 2 ee 6 18 xiv GemStone Systems Inc March 2006 Chapter 7 Managing Transactions 7 1 Transaction Management an Overview 2 eee ee ee 7 2 7 2 Operating Inside a Transaction 2 0 2 ee ee ee 7 3 Committing a Transaction 6 2 ee eee 7 4 Aborting a Transaction 2 2 a eee 7 5 Avoiding or Handling Commit Failures 7 5 7 3 Operating Outside a Transaction ooo ee 7 6 Being Signaled to Abort o ooo o 7 7 7 4 Transaction Modes 2 2 0 0 ee ee 7 8 Automatic Transaction Mode 0 0002 eee eee 7 8 Manual Transaction Mode 1 2 2 e 7 9 Choosing Which Mode to Use 2 0 2 ee ee eee 7 9 Switching Between Modes o ooo o 7 9 7 5
11. About GemBuilder Methods with substring Prompts for a string then opens a method browser showing all methods whose source contains that string Produces a submenu with the following options Users Symbol Lists Segments Opens the GemStone User Account Management Tools allowing you to create new users assign attributes to them and manage user accounts provided you have the privileges to do so The User Account Management Tools are described in Chapter 8 Opens a Symbol List Browser allowing you to examine and modify symbol dictionaries and their entries The Symbol List Browser is described in Chapter 8 Opens a Segment Tool allowing you to control authorization at the object level by assigning objects to segments The Segment Tool is described in Chapter 8 Produces a submenu with the following options Settings Breakpoints System Workspace Opens a Settings Browser in which you can examine change and store parameters for configuring GemBuilder The Settings Browser is described in Chapter 11 Opens a Breakpoint Browser allowing you to set and clear breakpoints in GemStone Smalltalk code The Breakpoint Browser is described on page 4 8 Opens the GemStone System Workspace a workspace containing a variety of useful GemStone Smalltalk and client Smalltalk expressions Opens a window providing the GemBuilder version and copyright information March 2006 GemStone Systems Inc
12. Example 5 3 TestObject class gt gt instVarMap super instVarMap stName gsName Appended to the inherited instance variable map a single pair declares that the instance variable stName in the client maps to the instance variable gsName in GemStone 5 16 GemStone Systems Inc March 2006 Sharing Objects Replicates One implementation can both prune irrelevancy and accommodate differing schemas as the instance variable mapping for the class Book shows in Example 5 4 Example 5 4 Book class gt gt instVarMap super instVarMap title title author author nil pages publisher nil copyright publicationDate Aa Stubbing The first two pairs of instance variables change nothing they explicitly state what would happen without this method but are included for completeness nil pages specifies that the client application does not need to know a books page count and therefore this server side instance variable is not replicated in the client publisher nil specifies that the client application needs and presumably assigns the instance variable publisher which is never replicated in the server copyright publicationDate maps the client class Book s instance variable copyright to the server class Book s instance variable publicationDate Often an application has need of certain instance variables but not all at once For example it s impractical to replicate t
13. GemStone s Smalltalk Namespace employee data Scope In Figure 6 2 objects a and b are root objects those objects from which all others can be reached by transitive closure by direct reference or by indirect reference through any number of layers The above discussion has focused on shared instances from your applications but in order to share instances in any way GemBuilder and GemStone must first share definitions for each class of shared instance Some connectors connect their objects whenever any session logs in some do so only when a specific session logs in e Global connectors allow you to maintain a standard set of connectors common to all applications in your GemBuilder image e Session connectors allow individual applications to customize connectors you define unique session parameters for each application and different sessions can connect different objects When sessions of one kind log in other sessions connectors are defined but not connected When a session logs in its session connectors and all global connectors if not already connected connect automatically When a session logs out its session connectors disconnect If the session is the last in the application to log out it disconnects the global connectors GemStone Systems Inc March 2006 Connectors Connecting Root Objects Verifying Connections Connectors are saved in client Smalltalk
14. GemStone GemBuilder for Smalltalk User s Guide For use with Cincom Smalltalk VisualWorks Environment Version 7 0 March 2006 GEMSTONE GemBuilder User Manual INTELLECTUAL PROPERTY OWNERSHIP This documentation is furnished for informational use only and is subject to change without notice GemStone Systems Inc assumes no responsibility or liability for any errors or inaccuracies that may appear in this documentation This documentation or any part of it may not be reproduced displayed photocopied transmitted or otherwise copied in any form or by any means now known or later developed such as electronic optical or mechanical means without express written authorization from GemStone Systems Inc Warning This computer program and its documentation are protected by copyright law and international treaties Any unauthorized copying or distribution of this program its documentation or any portion of it may result in severe civil and criminal penalties and will be prosecuted under the maximum extent possible under the law The software installed in accordance with this documentation is copyrighted and licensed by GemStone Systems Inc under separate license agreement This software may only be used pursuant to the terms and conditions of such license agreement Any other use may be a violation of law Use duplication or disclosure by the Government is subject to restrictions set forth in the Commer
15. Table 7 1 GbsSession Methods for Running Outside of a Transaction beginTransaction Aborts and begins a transaction transactionMode Returns autoBegin or manualBegin transactionMode newMode Sets autoBegin or manualBegin inTransaction Returns true if the session is currently in a transaction signaledAbortAction Executes aBlock when a signal to abort is aBlock received see below To begin a transaction send the message aGbsSession beginTransaction to begin a transaction for a specific session or GBSM beginTransaction to begin a transaction for the current session or in the Session Browser select a logged in session and click on the Begin button This message gives you a fresh view of the repository and starts a transaction When you abort or successfully commit this new transaction you will again be outside of a transaction until you either explicitly begin a new one or change transaction modes If you are not currently in a transaction but still want a fresh view of the repository you can send the message aGbsSession abortTransaction This aborts your current view of the repository and gives you a fresh view but does not start a new transaction Being Signaled to Abort When you are in a transaction GemStone waits until you commit or abort to reclaim storage for objects that have been made obsolete by your changes When you are running outside of a transactio
16. auditWithLimit findDisconnectedObjects markForCollection pagesWithPercentFree repairWithLimit scavengePagesWithPercentFree Repository March 2006 GemStone Systems Inc 8 29 GemStone Administration Tools GemBuilder User Manual 8 30 GemStone Systems Inc March 2006 Chapter Exception Handling This chapter discusses exceptions how to handle them and how to recover from them and how to define your own GemStone errors GemStone Errors and Exception Classes describes how GbsErrors and Exceptions are created and used Handling Exceptions explains how to handle exceptions and how to define and signal your own errors Interrupting GemStone Execution explains how to interrupt GemStone Execution 9 1 GemStone Errors and Exception Classes When an error occurs in the GemStone server an instance of GbsError is created that contains detailed information about the error and an exception is raised on that GbsError in GemBuilder You may set up exception handlers to catch the exception and perform the desired client Smalltalk exception handling If no exception handler is set up for the particular exception that occurred the default handler opens a notifier from which you can open a debugger March 2006 GemStone Systems Inc 9 1 GemStone Errors and Exception Classes GemBuilder User Manual GBS and GemStone server exceptions are represented in client Smalltalk by except
17. followed by arguments to the command line The NetLDI creates the named service by looking first for an entry in GEMSTONE bin services dat and then in the user s home directory for an executable having that name The NetLDI returns the network address of the service Authorization is needed to create a new process unless the NetLDI is in guest mode The task resource modifier is also used internally to create page servers dbf is used to access a database file The nrs body is the file spec of a GemStone database file The NetLDI creates a page server on the given node to access the database and returns the network address of the page server Authorization is needed unless the NetLDI is in guest mode spawn is used internally to start the garbage collection Gem process monitor is used internally to start up a shared page cache monitor file means the nrs body is the file spec of a file on the given host not currently implemented nrs body unformatted text to end of string The nrs body is interpreted according to the context established by the resource modifier No extended identifier expansion is done in the nrs body and no special escapes are needed C 6 GemStone Systems Inc March 2006 Appendix Client Smalltalk and GemStone Smalltalk This appendix outlines the few general and syntactical differences between the VisualWorks and GemStone Smalltalk languages GemStone Smalltalk and Client Sma
18. reeSlotsOnStubbing inherited from Object generateClassConnectors When true a session connector is automatically created to connect two classes one of which has been automatically generated in response to the presence of the other by the mechanisms described in the discussion of parameters generateClientClasses and generateServerClasses When false session connectors are not automatically created See Class Mapping on page 5 3 generateServerClasses When true if a client Smalltalk object is stored into GemStone and GemStone does not currently define the class of which it is an instance a corresponding class is defined in GemStone Smalltalk When false GemBuilder raises an error See Class Mapping on page 5 3 generateClientClasses When true if a GemStone server object is fetched into the client Smalltalk image and the client Smalltalk image does not currently define the class of which it is an instance a corresponding class is defined in the image When false behavior is defined by the client Smalltalk image See Class Mapping on page 5 3 InitialCacheSize The size in bytes of the initial cache for each GemStone session For best performance make this a prime number See Changing the Initial Cache Size on page 11 12 InitialDirtyPoolSize Initial size of the GbsSession dirtyPool identity set For bulk loading increasing this value reduces the number of times the set needs to grow For
19. 5 2 Class Mapping Before GemBuilder can replicate an object it must know the respective structures of client and repository object and the mapping between them Although not strictly necessary for forwarders this knowledge improves forwarding performance saving GemBuilder an extra network round trip during the initial connection March 2006 GemStone Systems Inc 5 3 Class Mapping GemBuilder User Manual GemBuilder uses class definitions to determine object structure To replicate an object e both client and server must define the class and e the two classes must be mapped using a class connector GemBuilder uses this mapping for all replication whether at login or later Unlike connectors for replicates or forwarders class connectors by default do not update at connect time If class definitions differ on the client and the server it is usually for a good reason you probably don t want to update GemStone with the client Smalltalk class definition or vice versa GemBuilder predefines special connectors called fast connectors for the GemStone kernel classes For more information about fast connectors see Connecting by Identity Fast Connectors on page 6 9 If there is no connector for a class and a mapping for that class is required GemBuilder will attempt to map the client and server classes with the same name By default it will also create a connector for those classes If the configuration parame
20. 7 3 Operating Outside a Transaction A session must be inside a transaction in order to commit While operating within a transaction every change the session makes and every new object it creates can be a candidate for propagation to the shared repository GemBuilder monitors the operations that occur within the transaction gathering all the necessary information required to prepare the transaction to be committed For efficiency an application may configure a session to operate outside a transaction When operating outside a transaction a session can view the repository browse the objects it contains and even make computations based upon their values but it cannot commit any new or changed GemStone server objects While operating outside a transaction a session saves some of the overhead of tracking changes which may be significant in some applications A session operating outside a transaction can at any time begin a transaction No session is overhead free even a session operating outside a transaction uses GemStone resources to manage its objects and its view of the repository For best system performance all sessions even those running outside a transaction must periodically refresh their views of the repository by committing or aborting GemStone Systems Inc March 2006 Managing Transactions Operating Outside a Transaction Table 7 1 shows GbsSession methods that support running outside of a GemStone transaction
21. A session refreshes its view of the shared object repository by aborting its transaction Despite the terminology a session need not be operating inside a transaction in order to abort To abort send the message aGbsSession abortTransaction to abort a specific session or GBSM abortTransaction to abort the current session or in the Session Browser select a logged in session and click on the Abort button or in the Class Browser use the pop up menu on the SymbolDictionary pane to select abort Aborting has these effects e The transaction if any ends If the session s transaction mode is automatic GemBuilder starts a new transaction If the session s transaction mode is manual the session is left outside of a transaction e Temporary Smalltalk objects remain unchanged e The session s private view of the GemStone shared object repository is updated to match the current state of the repository Avoiding or Handling Commit Failures You can use the GemBuilder method GbsSession gt gt hasConflicts to determine if any concurrency conflicts exist that would cause a subsequent commit operation to fail It returns false if it finds no conflicts with other concurrent transactions true otherwise You can then determine how best to proceed If an attempt to commit fails because of a concurrency conflict the commitTransaction method returns false Following a commit failure the client s view of persistent ob
22. GemStone s mechanism for implementing 3 4 GemStone Systems Inc March 2006 Using the GemStone Programming Tools Browsing Code namespaces This facilitates finding and sharing objects efficiently The symbol dictionaries that you can access are listed in the GemStone Browser s symbol list pane When you select a symbol dictionary in the Symbol List pane all classes defined in that dictionary appear in the Classes pane to the right Symbols other than classes can be viewed by opening an inspector on the symbol dictionary in question or by selecting GemStone gt Admin gt Symbol Lists GemStone Smalltalk categorizes methods by function to make them easier to browse When you select a class in the Classes pane a list of its method categories appears in the Method Categories pane to the right When you select a method category all the message selectors in that category appear in the rightmost Method Selectors pane As in the comparable client Smalltalk browsers you can switch focus between instance or class methods using the toggle or radio buttons provided Also as in the comparable client Smalltalk browsers when you select a method its source code is displayed in the lower portion of the browser the source pane In this pane you can edit and recompile the method set breakpoints in it or execute fragments of GemStone Smalltalk code as in a workspace Each pane of the GemStone Browser has pop up menus accessibl
23. GemStone Smalltalk code and accessing the GemStone programming tools Table 3 1 The GemStone Menu Browse Sessions Opens a GemStone Session Browser allowing you to log into or out of the GemStone server and manage transactions The Session Browser is described in Chapter 2 Browse Connectors Opens a GemStone Connector Browser allowing you to manage the connections between GemStone server and Smalltalk client objects The Connector Browser is described in Chapter 6 Browse Produces a submenu with the following options All Classes Class Namespace Senders of Implementors of References to Opens a GemStone Browser comparable to the client Smalltalk System or Classes Browser The GemStone Browser is described in Browsing Code on page 3 4 Prompts for the name of a class then opens a browser focused on that class Prompts for the name of a symbol dictionary then opens a browser focused on that dictionary Prompts for the name of a message selector then opens a method browser showing senders of that message Prompts for the name of a message selector then opens a method browser showing implementors of that message Prompts for the name of a variable then opens a method browser showing all methods that refer to that variable 3 2 GemStone Systems Inc March 2006 Using the GemStone Programming Tools GemStone Menu Table 3 1 The GemStone Menu Continued Admin Tools
24. It has no effect if the resource already exists If the log name is a relative path it is relative to the working directory If a log name is not set the pattern N P M log defined below is used See the earlier discussion of nrs identifier The argument to dir or log can contain patterns that are expanded in the context of the created resource The following patterns are supported H home directory M machine s network node name N executable s base name P process pid U user name W March 2006 GemStone Systems Inc C 5 Syntax GemBuilder User Manual resource modifier Hserver spawn task dbf monitor file Identifies the intended purpose of the string in the nrs body An NRS can contain only one resource modifier The default resource modifier is context sensitive For instance if the system expects an NRS for a database file then the default is dbf server directs the NetLDI to search for the network address of a server such as a Stone or another NetLDI If successful it returns the address The nrs body is anetwork server name A successful lookup means only that the service has been defined it does not indicate whether the service is currently running A new process will not be started Authorization is needed only if the NetLDI is on a remote node and is running in secure mode task starts a new Gem The nrs body is a NetLDI service name such as gemnetobject
25. applications that flush a small number of objects decreasing this value while keeping it larger than the number of objects being flushed improves flushing performance libraryName The name of the DLL or shared library to use to contact the server If the empty GemStone Systems Inc March 2006 Configuring GemBuilder string GBS loads the first found library with a default name It tries loading linked libraries first which support both linked and RPC logins then RPC only libraries If a libraryName is specified that exact library name is loaded If the library is not found an error is reported On Unix or Linux the library name may be specified as an absolute file path to the library file or as a simple name e g libgcirpc so On Windows use a simple name If a simple name is used the library is found in the platform specific standard directories for libraries This setting does not affect any library that is already loaded If a library is already loaded you will need to save your image quit and restart for a new libraryName to take effect pollForRpcResponse When using nonblocking protocol for RPC sessions this setting determines which method to use to detect when a response has been received from the GemStone server When true GBS uses a timed polling loop When false it waits for traffic on the socket that the gem uses for communication Under most circumstances the socket wait provides better latency a
26. connected objects synchronizing 6 18 connector 6 1 6 20 adding to session or global list 6 12 class 6 7 A 6 class versions and 5 6 connection order 6 8 forwarders and 5 6 update direction and 5 6 updating 5 4 class hierarchy 6 10 class instance variable 6 7 class variable 6 7 connecting object networks 6 2 connection order 6 8 controlling 6 13 creating automatically A 6 creating interactively 6 19 creating programmatically 6 10 defined 5 3 6 1 fast 6 9 for kernel classes 6 7 global 6 4 6 17 initializing 6 5 introduction to 1 4 list of 6 12 name 6 7 nilling 5 9 A 4 postconnect action 5 7 6 5 removing duplicates 6 5 removing invalid A 7 removing unresolved 6 18 scope 6 4 session 6 17 setting postconnect action programmatically 6 11 March 2006 GemStone Systems Inc Index 3 GemBuilder User Manual setup for initial storage of data in GemStone 6 20 updateGS postconnect action 6 20 updateST postconnect action 6 20 updating class definitions and 6 6 verifying 6 5 6 18 A 4 Connector Browser 6 16 6 20 updateGS postconnect action 6 20 updateST postconnect action 6 20 connectorNilling configuration parameter 5 9 A 2 A 4 connectVerification configuration parameter A 2 A 4 constraints circular 3 11 on instance variables 3 10 contexts 4 2 controlling the size of the client Smalltalk object cache 11 10 converting among forwarders stubs replicates and delegates 5
27. e use commas as separators and e can contain any valid GemStone Smalltalk expression as an element string one symbolOne c 4 Object new Exception handling In client Smalltalk exception handling is implemented by the Exception class hierarchy In GemStone it is implemented with a single class Exception An Exception in GemStone is an object that represents state to be invoked in the event of an exception There are two types of exceptions in GemStone In order of precedence they are 1 context exceptions and 2 static exceptions Static exceptions remain from run to run Context exceptions are active as long as the context to which the exception belongs is on your call stack when an exception is signaled Client Smalltalk exception handling is analogous to GemStone context exceptions All nonfatal errors can be trapped by a GemStone application Exception handling in VisualWorks is accomplished by sending Block gt gt on do In VisualWorks the argument to on is a predefined Exception class From within the handler block messages can be sent to the exception instance to cause the flow of control to resume exit the on do receiver block or restart the block D 2 GemStone Systems Inc March 2006 Index A abort GbsSession 7 4 7 5 GbsSessionManager 7 5 7 7 abort command 3 6 abort request from GemStone 7 7 abortErrLostOtRoot signal 7 8 abortTransaction GbsSession 7 8 addDependent 2
28. is permitted only one outstanding GemStone operation at a time 11 12 GemStone Systems Inc March 2006 Performance Tuning Multiprocess Applications When blockingProtocolRpc is true behavior is the same as in a linked session the execution process must wait for a GemStone call to return before proceeding One Process per Session Applications that limit themselves to one process per GemStone session are relatively easy to design because each process has its own view of the repository Each process can rely on GemStone to coordinate its modifications to shared objects with modifications performed by other processes each of which has its own session and own view of the repository For such applications setting processSafeCaches to true is the only additional precaution required If at all possible try to limit your application to one process per GemStone session Multiple Processes per Session Applications that have multiple processes running against a single GemStone session must take additional precautions You may not have designed your application to run multiple processes under a single GemStone session However if your application uses signals and notifiers chances are it is occasionally running two processes against a single GemStone session Methods that create concurrent processes include GbsSession gt gt notificationAction gt gt gemSignalAction gt gt signaledAbortAction When the specified ev
29. or the designated contacts have changed please contact us to update the appropriate user accounts Email support gemstone com Telephone 800 243 4772 or 503 533 3503 Requests for technical assistance may also be submitted by email or by telephone We recommend you use telephone contact only for more serious requests that require immediate evaluation such as a production system that is non operational In these cases please also submit your request via the web or email including pertinent details such error messages and relevant log files viii GemStone Systems Inc March 2006 If you are reporting an emergency by telephone select the option to transfer your call to the technical support administrator who will take down your customer information and immediately contact an engineer Non emergency requests received by telephone will be placed in the normal support queue for evaluation and response 24x7 Emergency Technical Support GemStone S offers at an additional charge 24x7 emergency technical support This support entitles customers to contact us 24 hours a day 7 days a week 365 days a year if they encounter problems that cause their production application to go down or that have the potential to bring their production application down Contact your GemStone S account manager for more details March 2006 GemStone Systems Inc ix GemBuilder User Manual GemStone Systems Inc March 200
30. to implement indexableSize as shown below otherwise the object storage mechanisms would try to iterate over the entire list of indexable slots rather than those controlled by firstIndex and last Index indexableSize self size Mapping Classes With Different Formats You can create a class in GemStone that maps to a client Smalltalk class with a different format for example a format of bytes on the client but pointers in the repository To do so reimplement the class method gsObjImp1 in the client Smalltalk to return a value specifying the GemStone implementation A gsObjImp1 method must return a SmallInteger representing the GemStone class format The following formats are valid Return Format 0 pointers 1 bytes 2 nonsequenceable collection Symbolic names for these values are stored in the pool dictionary SpecialGemStoneObjects Limits on Replication Replicating blocks and collections with instance variables can present special problems discussed below Replicating Client Smalltalk BlockClosures Forwarders are especially well suited for managing large collections that reside in the object server Collections are commonly sent messages that have blocks as arguments When the collection is represented in client Smalltalk by a forwarder these argument blocks are replicated in GemStone and executed in the server When a GemStone replicate for a client Smalltalk block is needed GemBuilder sends the block to Ge
31. transactions to commit successfully without locks but they do carry some overhead For one thing they use more storage than their ordinary counterparts Also you may find that your application takes longer to commit transactions when you use instances of these classes Finally you should be aware that under certain circumstances instances of these classes can hide conflicts from you that you indeed need to know about Because of the way these classes are implemented GemBuilder creates instances of these classes as forwarders rather than replicates Here are brief descriptions of the reduced conflict classes For details about these classes and their usage see the chapter in the GemStone Programming Guide entitled Transactions and Concurrency Control RcCounter RcCounter maintains an integral value that can be incremented or decremented A single instance of RcCounter can be shared among multiple concurrent sessions without conflict RcIdentityBag RclIdentityBag provides the same functionality as IdentityBag except that no conflict occurs on instances of RcIdentityBag when a number of users read objects in the bag or add objects to the bag at the same time Nor is there a conflict when one user removes an object from the bag while other users are adding objects or when a number of users remove objects from the bag at the same time so long as no more than one of them tries to remove the last occurrence of an object RcKey Valu
32. userAction 11 6 Changing the Initial Cache Size The GemStone configuration setting initialCacheSize is an integer that represents the pregrown size of the object caches whenever the caches are initialized The default is 5003 For best cache performance make initialCacheSize a prime number You can change the value of initialCacheSize by sending GbsConfiguration current initialCacheSize newValue or by modifying the setting using the Settings Browser 11 7 Multiprocess Applications Some applications support multiple Smalltalk processes running concurrently in a single image In addition some applications enter into a multiprocess state occasionally when they make use of signalling and notification Multiprocess GemBuilder applications must exercise some precautions in order to preserve expected behavior and data integrity among their concurrent processes Blocking and Nonblocking Protocol Ina linked GemBuilder session GemStone operations execute synchronously the application must wait for a GemStone operation to complete before proceeding with the execution process that called it Synchronous operation is known in GemBuilder as blocking protocol An RPC GemBuilder session can support asynchronous operation nonblocking protocol When the configuration parameter blockingProtocolRpc is false the default setting in RPC sessions client Smalltalk processes can proceed with execution during GemStone operations A session however
33. 11 11 arguments to 5 20 breakpoints and 4 7 private instance variables 3 15 Private Classes and Methods 1 10 privileges 8 3 Privileges Dialog 8 27 profiling GemStone Smalltalk execution 11 2 ProfMonitor class 11 2 programming interface 1 4 protecting methods 8 2 public methods 3 17 Published symbol dictionary 8 9 R ReBag 7 16 ReCounter 7 16 RcKeyValueDictionary 7 16 RcQueue 7 17 write write conflicts and 7 17 read lock messages readLock GbsSession 7 13 readLock ifDenied ifChanged GbsSession 7 13 readLockAll GbsSession 7 13 readLockAl1 ifIncomplete GbsSession 7 14 read operations 7 10 read set 7 10 read write transaction conflicts 7 10 7 16 reduced conflict classes 7 16 7 17 performance and 7 16 RcBag 7 16 RcCounter 7 16 RcKeyValueDictionary 7 16 RcQueue 7 17 storage and 7 16 reducing the number of objects in Smalltalk 11 9 registering a session 2 7 releasing locks 7 15 remote session 2 3 remove 10 9 removeDependent 2 14 removeFromCommitOrAbortReleaseLoc ksSet System 7 15 removeFromCommitReleaseLocksSet System 7 15 removelnvalidConnectors configuration parameter A 2 A 7 removeLock GbsSession 7 14 removeLockAl1l GbsSession 7 14 removeLocksForSession GbsSession 7 14 removeMakeGSTransparent 5 13 removeMarkDirtyOnAtPut 5 13 removeMarkDirtyOnInstvarAssign 5 13 removeParameters GbsSession 2 7 removin automatic dirty marking 5 13 duplicate c
34. 14 adding connector to session or global list 6 12 addParameters GbsSession 2 7 addToCommitOrAbortReleaseLocksSet System 7 15 addToCommitReleaseLocksSet System 7 15 alwaysUseGemCursor configuration parameter A 1 A 3 application design 1 7 1 9 5 2 6 4 argument in message to forwarder 5 8 array constructors in GemStone Smalltalk E 2 assertionChecks configuration parameter A 1 A 3 assigning a migration destination 10 3 at put and object synchronization 5 12 authorization 8 6 8 7 and migration 10 4 autoMarkDirty configuration parameter A 1 A 3 automatic class generation 5 4 5 5 A 6 disabling 5 5 automatic mark dirt in VisualWorks 5i 5 12 in VisualWorks 7 x 5 11 automatic transaction mode 7 8 7 9 defined 7 8 basicAt put and object synchronization 2 block callback 5 35 replicating 5 31 A 4 March 2006 GemStone Systems Inc Index 1 GemBuilder User Manual blockingProtocolRpc configuration parameter A 1 A 3 blockReplicationEnabled configuration parameter 5 32 A 1 A 3 blockReplicationPolicy configuration parameter A 1 A 4 Breakpoint Browser 4 8 4 9 breakpoints 4 2 4 8 and primitive methods 4 7 and special methods 4 7 methods that cannot have 4 7 bulkLoad configuration parameter A 2 A 4 business objects 1 8 C cache size changing 11 12 size initial A 6 space management 11 10 cache inventory statistics 11 5 callback for blocks 5 35 changed object no
35. 2 GemStone System Workspace lt gt Workspace lol x Page i Edit Smalltalk Options Help AMAIA EE Gemstone System Workspace Variables GemStone Session Control GBSM login Login to GemStone GBSM logout Logout of GemStone GBSM isLoggedin See if you are logged into GemStone GBSM currentSession Current active GSSession GemStone Transactions GBSM commitTransaction Commit transaction of the default session GBSM abortTransaction Abort transaction of the default session GBSM transactionMode autoBegin A new transaction starts after each commit abort default GBSM transactionMode manualBegin Don t automatically begin a transaction after commit abort GBSM beginTransaction Used to begin transaction in manual mode Performs an Text or Smalltalk code 3 4 Coding This section explains how to define new GemStone classes and methods and describes aspects of coding unique to GemStone Smalltalk About GemStone Smalltalk Classes The following discussion summarizes the main differences between GemStone Smalltalk and client Smalltalks For complete information about programming in GemStone Smalltalk refer to the GemStone Programming Guide Instance variables can be constrained To speed GemStone Smalltalk s indexed associative access for efficient querying you can constrain the value of an instance variable to contain only specified kinds of objects Constraining a var
36. 39 copyEmpty implementing for collections with instance variables 5 36 create access 10 9 create access command in Browser s Class menu 3 8 create in ST 10 9 create in ST command in Browser s Class menu 3 8 3 9 creating connector interactively 6 19 connector programmatically 6 10 forwarder 5 7 forwarder interactively 6 19 linked session 2 6 remote session 2 6 subclasses 3 12 CstMessengerSupport parcel 1 9 current segment 8 6 current session 2 11 setting 2 13 tools attached to 2 12 D data cost of managing 11 7 modifying shared 5 10 7 10 storage in GemStone 6 20 debug command 4 10 debugger 4 1 4 9 debugging 4 1 4 10 forwarders A 5 getting stack trace without debugger 4 10 stubs A 8 decompiled method viewing 5 12 default segment 8 5 defaultFaultPolicy configuration parameter 5 20 A 2 A 5 defining GemStone errors 9 4 definition 10 8 defunct forwarder 5 8 during packaging B 2 defunct stub 5 21 during packaging B 2 delegate converting 5 39 Delivery and Deployment 1 9 dependencies between objects managing with replication specififcations 5 25 dependents session 2 13 2 17 adding 2 14 committing a transaction 2 13 removing 2 14 Deprecated Features 1 10 1 11 deprecated 1 10 deprecationWarnings configuration parameter 1 11 A 2 A 5 dictionaries Globals 8 9 pool 3 12 Published 8 9 shared 8 9 8 10 specifying for a new class 3 13 UserGlobals 8 9 Index 4 GemStone Systems Inc Marc
37. 8 password GemStone 2 5 2 7 host 2 6 performance 1 9 changing the initial cache size and 11 12 choosing execution platform 5 2 choosing the execution platform and 11 7 client Smalltalk primitives and 11 11 controlling fault level and 11 8 controlling replication level and 5 17 controlling the locus of execution and 11 6 cost of data management and 11 7 database searching and sorting 11 8 determining bottlenecks 11 2 enhancing replication 5 14 explicit stubbing and 5 20 11 10 fault levels and 11 8 forwarders and 11 11 GemStone Smalltalk user actions and 11 11 minimizing faulting of dirty GemStone objects 11 8 minimizing replication cost 5 14 5 27 multiprocess applications and 11 12 preventing transient stubs 11 9 reduced conflict classes and 7 16 reducing conflict and 7 16 statistics gathering for tuning 11 2 traversal buffer size and 11 9 using forwarders 5 6 using GemStone Smalltalk for searching and sorting large objects 11 8 pollForAsynchronousEvents configuration parameter A 2 A 7 pollForRpcResponse configuration parameter A 2 A 7 pool dictionaries 3 12 pool variables 3 12 March 2006 GemStone Systems Inc Index 9 GemBuilder User Manual postconnect action 6 5 changing 6 19 setting programmatically 6 11 updateGS 6 20 postFault 5 28 precedence of multiple replication specifications 5 26 of replication mechanisms 5 36 preFault 5 28 prerequisites 1 iv preventing transient stubs 11 9 primitives
38. Administration Tools GemBuilder User Manual Figure 8 5 GemStone User Dialog l01x File User Help User ID Lisa v Password Native Language English Privileges Paste To Default Segment Group Membership Add To New Group ove Fro Publishers Table 8 11 shows the operations that are available in this dialog Table 8 11 Buttons in the GemStone User Dialog Privileges Brings up a Privileges Dialog in which you can select privileges for this user Paste To Default Makes the grabbed segment from the Segment Tool Segment the default segment for this user Add to Group Allows you to select a group name from a menu of known groups and adds this user to that group Add To New Group Prompts you for a new group name and adds this user to the group Remove From Removes this user from the selected group Group Show Symbol List Brings up a Symbol List Browser for the designated user Show Segments Brings up a Segment Tool 8 26 GemStone Systems Inc March 2006 Security and Object Access GemStone Administration Tools The User Dialog has three menus File User and Help menus The File menu contains the following items Table 8 12 GemStone User Dialog File Menu Commit Makes all changes in the current transaction permanent Abort Aborts the current transaction Update Causes the dialog to
39. Automatically in VW 7 x 5 11 Marking Modified Objects Dirty Automatically in VW 5i 5 12 Marking Modified Objects Dirty Manually 5 14 Minimizing Replication Cost 2 0 0 0 0 ooo o 5 14 Instance Variable Mapping o ooo o 5 15 StUDDIN Gs cb ea a dni 5 17 March 2006 GemStone Systems Inc xiii GemBuilder User Manual Replication Specifications o ooo ooo 5 21 Customized Flushing and Faulting o o 5 27 Modifying Instance Variables During Faulting 5 27 Modifying Instance Variables During Flushing 5 29 Mapping Classes With Different Formats 5 31 Limits on Replication o ooo ooo o o 5 31 Replicating Client Smalltalk BlockClosures 5 31 Block Callbackses sesh ease e ta amp Me eee 5 35 Replicating Collections with Instance Variables 5 36 5 5 Precedence of Replication Mechanisms ooo 5 36 5 6 Evaluating Smalltalk Code on the GemStone server 5 37 5 7 Converting Between Forms aaua ooo 5 39 Chapter 6 Connectors 6 1 Connecting Root Objects 1 ooo e 6 2 SCOPES ty teats Geode a he eh GA oe tom Dall to SS coh 6 4 Verifying Connections ooo 6 5 Initializing es 3 61 eras eb ae wea ee eee a tes 6 5 Updating Class Definitions o o o ooo 6 6 6 2 Connecting and Disconnecting oo ooo 0000 6 6 6 3 Kinds of Connectors
40. Messages On the client when a forwarder to the server receives a message it sends the message to its counterpart on the GemStone server presumably an instance that can respond meaningfully The target server object s response is then returned to the forwarder on the client which then returns the result When a forwarder to the client receives a message on the server it forwards the message to the full fledged client object to which it is connected This object s response is returned to the client forwarder which returns the result represented as a server object March 2006 GemStone Systems Inc 5 7 Forwarders GemBuilder User Manual Arguments Before a message is forwarded to the GemStone server arguments are translated to server objects As a message is forwarded to the client its arguments are translated to client Smalltalk objects When an argument is a block of executable code special care is required for details see Replicating Client Smalltalk BlockClosures on page 5 31 Results The result of a message to a client forwarder is a GemStone Smalltalk object in the GemStone server The result of a message to a server forwarder is the client Smalltalk object connected to the server object returned by GemStone usually a replicate although a forwarder might be desirable under certain circumstances To ensure a forwarder result prefix the message to the forwarder with the characters fw For exam
41. Smalltalk debugging facilities similar to the debugging aids supplied by the client Smalltalk This chapter describes the important differences between them Inspectors describes how to view and modify the instance variables of server objects Breakpoints describes breakpoints setting breakpoints and using the Breakpoint Browser Debugger describes GemBuilder s enhanced debugger and how to get a stack trace without a debugger Some of the tools described are specific to VisualWorks 7 x 4 1 Debugging Overview GemBuilder s debugging tools assist you in examining and modifying application objects during execution These facilities enable you to perform the following operations March 2006 GemStone Systems Inc 4 1 Inspectors GemBuilder User Manual e You can view and alter the instance variables of server objects e You can step through execution of a method examining the values of arguments temporaries and instance variables after each step e You can set clear and examine GemStone Smalltalk breakpoints When a breakpoint is encountered during normal execution a notifier appears and you can open a debugger with which you can interactively explore the contexts in the stack at the time execution halted e Youcan inspect or change the values of arguments temporaries and receivers in any context stack frame on the virtual machine call stack then continue execution from the top of the stack This means th
42. Supplying Session Parameters o o ooo 2 8 Removing Session ParameterS o oo oo 2 9 2 5 Logging In To and Logging Out Of GemStone o oo ooo 2 10 Logging In To GemStone Programmatically 2 10 The Current Session 2 2 11 Logging Out of GemStone Programmatically 2 12 Session Management Using the Session Browser 2 12 Logeing In 46 6 4 exile Sawa nd Maw ee Me ee 2 12 Setting the Current Session o oo o 2 13 Logging Out of a GemStone Session With the Session Browser 2 13 2 6 Session Dependents o ooo 2 13 Chapter 3 Using the GemStone Programming Tools Bl GemStone Menu 2 1 eaa aTa E E a a an D e D ar e e a dai eN 3 2 3 2 Browsing Codecs S s soe avin e EE BS POR Sota ara Et Ss 3 4 Symbol List Pane 2 an ai h a E ee 3 6 Class Dan s a ee haa ee ee babe a Le ae hae eed 3 7 Pop up Text PaneMenu 2 ooo 3 8 3 3 The System Workspace lt sa sis sore ee 3 9 SAC OIIE hes Oak a CR Bae tees dk NUN Gp tt WOR Mae Bhd Sas Ol de toe ed na 3 10 About GemStone Smalltalk Classes 3 10 Defining a New Class gege ee ee 3 12 Subclass Creation Methods o 3 14 Private Instance Variables 3 15 Modifying an Existing Class o ooo o ee 3 15 Defining Methods e doe teus a ee A a ae 3 17 Public and Private Methods 3 17
43. Systems Inc March 2006 Profiling Client Smalltalk Execution 11 2 Main Statistics ud a a de Geena amp RE ES ee As 11 3 Cache Inventory Statistics 2 2 ee en 11 5 VSD ss IS E am SS ees GE AAS as aah Ad UE ce og A 11 6 11 2 Selecting the Locus of Control 2 2 ee 11 6 Locus of Execution inak aoe E ee 11 6 Relative Platform SpeedS ooo oo 11 7 Cost of Data Management oo o 11 7 GemStone Optimization o oo 11 8 11 3 Replication Tuning ce 2 4 fnew a EE ER Owes 11 8 Controlling the Fault Level 2 0 0 2 ee eee 11 8 Preventing Transient Stubs oo o 11 9 Setting the Traversal Buffer Size o oo o 11 9 11 4 Optimizing Space Management o oo 11 9 Explicit Stubbing Laa pea o A 11 10 Using ForwarderS o ooo e 11 11 IS USNE PrMilVeSi Mead aca ar e ae go ae 11 11 11 6 Changing the Initial Cache Size o ooo 11 12 11 7 Multiprocess Applications o ooo o 11 12 Blocking and Nonblocking Protocol 11 12 One Process per Sessi0N o oo mo 11 13 Multiple Processes per Session o ooo 000000048 11 13 Coordinating Transaction Boundaries 11 14 Coordinating Flushing o 11 14 Coordinating Faulting o ooo e 11 14 Using the VisualWorks Application Model
44. Tools Coding o Remove existing behavior from Address doit Address removeAllMethods Address class removeAllMethods l Class methods for Address Instance methods for Address category Accessing method Address street Return the value of the street o category Updating method Address street newValue Modify the value of the street newValue category Accessing method Address zip Return the value of the SZTP 6 category Updating method Address zip newValue Modify the value of the zip newValue o instance instance instance instance variable variable variable variable street street zip ah zip A GemStone s filing out and filing in facilities are intended mainly for saving and restoring classes and methods without manual intervention Ifthisis all you want March 2006 GemStone Systems Inc 3 19 Coding GemBuilder User Manual to do then you don t need to understand the Topaz commands involved However it is also possible to create custom files that include commands to commit transactions and to create and manipulate objects other than classes and methods If you want to perform such tasks refer to the Topaz Programming Environment The file in mechanism cannot execute the full set of Topaz commands it s limited to the following subset
45. _and _trapOop To set breakpoints GemBuilder provides the Breakpoint Browser To debug the resulting stack GemBuilder enhances the client Smalltalk debugger The Breakpoint Browser You can set breakpoints in the source code pane of any browser using the set break menu item described in Table 3 4 on page 3 8 You can also use the breakpoint browser which lets you set clear and examine breakpoints for all classes and methods After you ve set a breakpoint for further convenience you can use the menu items to disable or re enable all breakpoints or just selected ones A breakpoint browser has two panes the list of break points on top and the source code associated with the selected breakpoint on the bottom Figure 4 5 shows an example 4 8 GemStone Systems Inc March 2006 Debugging Debugger Figure 4 5 GemStone Breakpoint Browser with a Breakpoint GemStone Breakpoint Browser Oo x Ed WriteStream gt gt nextPut 3 gt nextPut anObject Inserts anObject as the next element that the receiver can access for writing Returns anObject itsCollection at position put anObject d position position A i anObject v The Break Pane The break pane displays a scrollable list of the active breakpoints The items in the list look like this 1 WriteStream gt gt nextPut 3 In this example a method break is set at step point 3 within the method next Put d
46. an Existing Class If you select an existing GemStone Smalltalk class then modify and save the class definition you create a new version of that class and all of its subclasses The browser attempts to recompile all methods from the previous version into the new version Methods that fail to recompile are presented in a method list browser March 2006 GemStone Systems Inc 3 15 Coding GemBuilder User Manual from which you can correct the errors If the class has subclasses they are also versioned and their methods recompiled Versioning a class does not migrate its instances they re still instances of the old class You can migrate some or all instances of one version of a class to another version explicitly For more information on migrating instances see the chapter entitled Class Versions and Instance Migration in the GemStone Programming Guide NOTE You can only modify classes for which you have write authorization To create a new version of a class Step 1 Select the class in the browser to bring up its definition in the source pane Step 2 Edit the definition as required Step 3 Select Save or accept from the pop up menu Whenever you create a class with the same name as a class that already exists in one of your symbol dictionaries the new class is automatically created as the latest version of the existing class and it automatically shares the same class history Instances created after the r
47. and commits In general you should remove a lock on an object when you have used the object committed the resulting values to the repository and no longer anticipate a need to maintain control of the object The following methods are used to remove specific locks aGbsSession removeLock anObject aGbsSession removeLockAl11 aCollection aGbsSession removeLocksForSession 7 14 GemStone Systems Inc March 2006 Managing Transactions Managing Concurrent Transactions The following methods answer various lock inquiries aGbsSession sessionLocks aGbsSession systemLocks aGbsSession lockOwners anObject aGbsSession lockKind anObject Releasing Locks Upon Aborting or Committing The following statements add a locked object or the locked elements of a collection to the set of objects whose locks are to be released upon the next commit or abort aGbsSession addToCommitReleaseLocksSet aLockedObject aGbsSession addToCommitOrAbortReleaseLocksSet aLockedObject aGbsSession addAl1ToCommitReleaseLocksSet aLockedCollection aGbsSession addAl1ToCommitOrAbortReleaseLocksSet aLockedCollection If you add an object to one of these sets and then request a fresh lock on it the object is removed from the set You can remove objects from these sets without removing the lock on the object The following statements show how to do this aGbsSession removeFromCommitReleaseLocksSet aLockedObject aGbsSession re
48. and managing GemStone sessions Chapter 3 Using the GemStone Programming Tools explains how to use the GemStone browsers and tools to create classes and methods in GemStone and to debug GemStone Smalltalk code Chapter 4 Debugging explains breakpoints and other ways you can use GemBuilder tools to debug your application Chapter 5 Sharing Objects describes the various mechanisms GemBuilder can use to coordinate your application s local objects with objects in the GemStone object server thus making them persistent and sharable Chapter 6 Connectors explains how to connect your application s local objects to objects in the GemStone repository in order to implement object sharing and allow your application to manipulate objects in the server Chapter 7 Managing Transactions discusses the process of committing a transaction the kinds of conflicts that can prevent a successful commit and how to avoid or resolve such conflicts iv GemStone Systems Inc March 2006 Chapter 8 Security and Object Access describes the security mechanisms that are available in GemBuilder and explains how to control access to objects in a multiuser environment It explains how to use the GemBuilder tools to manage access to objects and administer user accounts Chapter 9 Exception Handling discusses errors how to handle them and how to recover from them Chapter 10 Schema Modification and Coordination explains how GemStone supp
49. and moving versions to another class history A Symbol List Browser allows you to examine the GemStone Symbol Lists associated with UserProfiles add and delete dictionaries from these lists and manipulate the entries in those dictionaries A User Account Management Tool allows you to create new user accounts change account passwords and assign group membership A Segment Tool facilitates managing GemStone authorization at the object level by controlling how objects are assigned to segments GemStone Systems Inc March 2006 Basic Concepts Designing a GemStone Application an Overview 1 3 Designing a GemStone Application an Overview Many GemStone users start with an application they have already written in Smalltalk Their mission is to transform that application into one that makes meaningful use of GemStone s features persistence multiuser access security integrity and the ability to store and manage large quantities of information As a GemStone programmer your application design and porting efforts involve the following tasks e choosing the objects that should be stored and shared e deciding which objects need to be secured e establishing connections between root objects in the client and the server e deciding when to commit transactions and how to handle concurrency control and e tuning your application for optimal performance This section gives you an overview of these steps and points you to th
50. and replicates Forwarder Replicate Stub Connector is a proxy a simple object that knows only which object in the other space it is associated with It responds to a message by passing it to its associated master object in the other object space where state is stored and execution occurs remotely Forwarders can be on the client for server master objects or on the server for client master objects is an object associated with a particular object in the other object space The replicate copies some or all of the other object s state which it synchronizes at appropriate times it implements all messages it expects to receive it executes locally is a proxy that responds to a message by becoming a replicate of its counterpart object then executing the message locally Stubbing is a way to minimize memory use and network traffic by bringing only what is needed when it is needed associates a root client object with a root server object typically resolving objects by name although there are other ways When connected they synchronize data or pass messages in either direction or take no action at all as specified For more information on connectors see Chapter 6 Whatever combination of these elements your application requires subsystems of objects will probably reside on both the client and the server Some subset of these subsystems will need state or behavior on both sides some objects will be shared
51. authorization 8 2 privileges 8 3 protecting methods 8 2 Segment class 8 4 Segment Tool 8 10 8 11 8 18 changing a default segment 8 19 changing authorization 8 18 displaying segments 8 12 examining authorization 8 18 File menu 8 14 Group menu 8 16 Help menu 8 17 Member menu 8 16 Report menu 8 17 Segment menu 8 15 segments and authorization 8 6 8 7 changing authorization 8 18 checking authorization 8 18 group assignment 8 13 Segment Tool 8 10 8 11 selection blocks in GemStone E 2 selector reserved 3 17 session 2 1 2 17 control 2 4 classes for 2 4 creating linked 2 6 creating remote 2 6 current 2 2 2 11 2 13 dependents 2 13 2 17 adding 2 14 committing a transaction 2 13 removing 2 14 login information 2 9 linked 2 3 schema March 2006 GemStone Systems Inc Index 11 GemBuilder User Manual logging in interactively 2 12 programmatically 2 10 logging out interactively 2 13 programmatically 2 12 managing connectors for 6 13 multiple 2 3 2 11 persistence of notify set in 7 17 registering with GBSM 2 7 remote 2 3 removing 2 9 RPC 2 3 seeing others changes 5 19 signaling between 7 18 supplying parameters with Session Paramters Editor 2 8 tools attached to current 2 12 Session Browser 2 8 2 13 opening 2 8 starting 2 8 session main Statistics 11 3 Session Manager main statistics 11 3 session parameters 2 5 2 7 adding connectors and 6 15 adding new 2 8 See also GbsSessionParameters Sessio
52. block block2 The following statements request locks on each element in the three different collections aGbsSession readLockAl1 aCollection aGbsSession writeLockAl11 aCollection aGbsSession exclusiveLockAl1 aCollection March 2006 GemStone Systems Inc 7 13 Managing Concurrent Transactions GemBuilder User Manual The following statements request locks on a collection acquiring locks on as many objects in aCollection as possible If you do not have the proper authorization for any object in the collection an error is generated and no locks are granted aGbsSession readLockAl1 aCollection ifIncomplete block1 aGbsSession writeLockAl1 aCollection ifIncomplete block1 aGbsSession exclusiveLockAl1 aCollection ifIncomplete block1 Example 7 1 shows how error handling might be implemented for the collection locking methods Example 7 1 getWriteLocksOn aCollection This method attempts to set write locks on the elements of a Collection aGbsSession writeLockA11 aCollection ifIncomplete result result a 1 isEmpty ifFalse self handleDenialOn denied result at 2 isEmpty ifFalse aGbsSession abortTransaction result at 3 isEmpty ifFalse aGbsSession abortTransaction Once you lock an object it normally remains locked until you either log out or explicitly remove the lock unless you specify otherwise locks persist through aborts
53. buffers you define in these methods are used during faulting They are subsequently unpacked by the faulted object according to its implementation of the unpacking methods listed above Implement the unpacking methods to obtain the desired client representation by performing arbitrary computation on the buffer contents Use the message namedValues indexableValues for cases in which computation must operate on indexable and named values together NOTE The methods namedValuesBuf fer and namedValues area pair so are indexableValuesBuffer and indexableValues To avoid replication errors if you override one you must also override the other You can also override the messages indexableValueAt put and namedValueAt put to process the values of the indexable and named slots of the object For example class Set might implement the former as Set gt gt indexableValueAt index put aValue self add aValue The method simply adds the element to the Set rather than assigning it to a specific slot NOTE To avoid generating a previous flush did not complete error if you override namedValues or indexableValues make sure you do not send messages to any stubs that would require a remote object to be faulted Doing so causes an error as faulting is attempted while flushing Adjust the replicationSpec and faultPolicy of the object to ensure that stubs won t exist for special flush operations You can override two other messages to c
54. client Block callbacks escape the documented limitations of block replication but do not perform well for blocks invoked repeatedly from GemStone bulkLoad When true newly created objects are stored in GemStone as permanent objects immediately bypassing a step wherein they are temporary and eligible for storage reclamation by the GemStone garbage collector unless other objects refer to them in which case they become permanent objects as usual Bypassing this step improves performance for bulk data loading When false the temporary object step is not bypassed confirm When true you are prompted to confirm various GemBuilder actions Leave set to true during application development deployed applications may set to false connectorNilling When true GemBuilder nils the Smalltalk object for certain session based connectors after logout all name class variable or class instance variable connectors whose postconnect action is updateST or forwarder When the last session logs out the Smalltalk object references of global connectors are also set to nil Fast connectors class connectors and connectors whose postconnect action is updateGS or none are not set to nil Clearing connectors that depend on being attached to GemStone server objects helps prevent defunct stub and forwarder errors When false the logout sequence leaves the state of persistent objects in the image as it was connectVerification When true connectors verif
55. confirmation to proceed asks if the user wants to migrate instances If yes prompts for the migration target migrates the instances and updates the browser create access Creates methods for accessing and updating the instance variables of the currently selected class version create in ST Generate the selected class in client Smalltalk if a mapping doesn t already exist If it does exist executing this menu item has no effect compile in ST Attempts to compile all methods instance and class of selected class version in corresponding client Smalltalk class update Update the browser to the current view of the class versions inspect instances Open an inspector on instances on the selected version migrate instances Migrate all instances of the selected versions Prompts you to select which version to migrate to The user can only migrate to another version of the same class history so if all versions are selected there is no migration destination and the item should be grayed out Otherwise prompt for the version to migrate to by popping up a list of versions not selected Allow the user to cancel the operation by clicking a cancel button March 2006 GemStone Systems Inc 10 9 The Class Version Browser GemBuilder User Manual 10 10 GemStone Systems Inc March 2006 Chapter 11 Performance Tuning This chapter discusses ways that you ca
56. could have changed since last login Which value is valid Connectors can initialize either object by performing a specified postconnect action Update Smalltalk default for all but class connectors initializes the client object with the current state of the GemStone server object Update GemStone initializes the GemStone server object with the current state of the client object March 2006 GemStone Systems Inc 6 5 Connecting and Disconnecting GemBuilder User Manual Forward to the server or client makes one object a forwarder to the other Forwarders are discussed starting on page 5 6 No initialization leaves the client object and GemStone server object unmodified after connection default for class connectors As the name implies postconnect actions execute only at initial connection After that changes propagate according to mark dirty specifications as described in Synchronizing State on page 5 10 or they do not propagate at all as is normally the case with class connectors as described in Class Mapping on page 5 3 Updating Class Definitions By default after login and initialization class connectors do not propagate changes If you ve defined classes differently on the client and the server you probably had good reason to do so you probably don t want one object space to update the other with its own class definition Therefore to avoid updating class definitions class connectors ge
57. default mapping to accommodate nonstandard situations If you later change either of the mapped class definitions GemBuilder automatically remaps identically named instance variables Behavior Mapping When GemBuilder generates classes automatically it only copies the definition of the class not the methods of the class Replicated instances depend on methods implemented in the object space in which they execute During development it may be simplest to use GemBuilder s programming conveniences to implement the same behavior in both spaces For reliability and ease of maintenance however some decide to remove unnecessary duplication from production systems and to define behavior only where it executes March 2006 GemStone Systems Inc 5 5 Forwarders GemBuilder User Manual Mapping and Class Versions Unlike the client Smalltalk language GemStone Smalltalk defines class versions when you change a class definition you make a new version of the class which is added to an associated class history For details see the chapter entitled Class Versions and Instance Migration in the GemStone Programming Guide If you decide to update one class definition with the other the result depends on the direction of the update e Updating a client Smalltalk class from a GemStone server class regenerates the client class and recompiles its methods e Updating a GemStone server class from a client Smalltalk class cre
58. errors 9 4 UserGlobals symbol dictionary 8 9 username GemStone 2 5 host 2 6 UserProfile class 8 5 V variables pool 3 12 shared 3 12 verbose configuration parameter A 2 A 8 verifying connectors 6 18 versions of classes 10 2 10 6 connecting and 5 6 mapping and 5 6 replication specifications and 5 23 VisualWorks 5i Settings Browser A 11 VisualWorks 7 x Settings Browser A 9 VSD visual stat display 11 6 March 2006 GemStone Systems Inc Index 13 GemBuilder User Manual W write lock messages writeLock GbsSession 7 13 writeLock ifDenied ifChanged GbsSession 7 13 writeLockAll GbsSession 7 13 writeLockAl1 ifIncomplete GbsSession 7 14 write operations 7 10 write set 7 10 write write transaction conflicts 7 10 7 16 RcQueue and 7 17 Index 14 GemStone Systems Inc March 2006
59. even an occasional inability to commit then using locks might be your best choice Locks do not prevent read only access to objects so read only query transactions are not affected by modification transactions Setting the Concurrency Mode Any shared object that is not explicitly locked is treated optimistically For objects under optimistic concurrency control GemStone s level of checking for concurrency conflicts is configurable You can set the level of checking for concurrency conflicts by specifying one of the following values for the CONCURRENCY_MODE configuration parameter in your application s configuration file There are two levels e FULL_CHECKS the default mode which checks for both write write and read write conflicts If either type of conflict is detected your transaction cannot commit e NO_RW_CHECKS which performs write write checking only Locking methods override the configured optimistic CONCURRENCY_MODE by stating explicitly the kind of pessimistic control they implement 7 12 GemStone Systems Inc March 2006 Managing Transactions Managing Concurrent Transactions Setting Locks GemBuilder provides locking protocol that allows application developers to write client Smalltalk code to lock objects and specify client Smalltalk code to be executed if locking fails A GbsSession is the receiver of all lock requests Locks can be requested on a single object or on a collection of objects Single
60. from the Gemstone menu or click on the Show Symbol List button on a GemStone User Dialog Like the other GemStone tools the Symbol List Browser opens on a particular login session When a Symbol List Browser instance is created it is attached to the current GemStone session and remains attached to that session until the browser is closed Figure 8 3 shows the Symbol List Browser Figure 8 3 The Symbol List Browser Symbol List Browser loj xj Fie Mode Edit Object Help Symbol List for l DataCurator l v Dictionaries 247 Entries UserGlobals AbstractCharacter al Published UserClasses AbstractSession AbstractUserProfileSet AbstractCollisionBucket AbstractDictionary Selected Dictionary Globals aSymbollstDictionary segment Number 2 in Repository SystemRepository Owner DataCurator write World read Mv The field labeled Symbol List for contains a list of all the GemStone users that are visible to the session to which the browser is attached When you select a GemStone user name a list of the dictionaries in that user s SymbolList is displayed in the Dictionaries pane GemStone permissions are observed any 8 20 GemStone Systems Inc March 2006 Security and Object Access GemStone Administration Tools dictionaries in that SymbolList that are not normally accessible to the browser s session will not be visible in the list When a dictionary is selected the
61. in an NRS by preceding the name of the variable with If the name needs to be followed by alphanumeric text then it can be bracketed by and If an environment variable named foo exists then either of the following will cause it to be expanded foo or 00 Environment variables are only expanded in the nrs header The nrs body is never parsed address modifier protocol node Specifies where the network resource is protocol tcp decnet serial default Supports heterogeneous connections by predicating address on a network type If no protocol is specified GCILNET_DEFAULT_PROTOCOL is used On UNIX hosts this default is tcp node nrs identifier If no node is specified the current machine s network node name is used The identifier may also be an Internet style numeric address For example tcp 120 0 0 4 server cornerstone nrs identifier identifier Identifiers are runs of characters the special characters and white space blank tab newline must be preceded by a Identifiers are words in the UNIX sense keyword modifier authorization modifier environment modifier Keyword modifiers may be given in any order If a keyword modifier is specified more than once the latter replaces the former If a keyword modifier takes an argument then the keyword may be separated from the argument by a space or a colon C 4 GemStone Systems Inc March 2006
62. index lt size whileTrue 46 48 7 9 index index 1 11 10 found value self at index 14 13 412 Ji found 415 If you use the GemStone debugger described starting on page 4 9 to step through this method the first step takes you to the point where includesValue is about to be sent Stepping again sends that message and halts the virtual machine at the point where found is assigned Another step sends that message and halts the virtual machine just before the result is assigned to index and so on When the GemStone Smalltalk virtual machine encounters an enabled breakpoint during normal execution GemStone either displays a notifier in which selecting Debug in the notifier opens a GemStone Debugger or opens the GemStone Debugger directly depending on the client Smalltalk version In the Debugger you can interactively explore the context in which execution halted Special considerations apply in setting breakpoints for primitive and special methods GemStone Systems Inc March 2006 Debugging Breakpoints Breakpoints for Primitive Methods If you set a breakpoint in a primitive method the break is encountered only if the primitive fails Consider the method below aString lt primitive 160 gt self _primitiveFailed When this method is invoked GemStone first executes the machine code in primitive 160 If that code executes successfully the primitive is said to succeed and th
63. noticeably improve performance Clearly there is a cost for faulting objects into the client Smalltalk This is made up of communication cost with GemStone object accessing in GemStone object creation and initialization in the client Smalltalk and increased virtual machine requirements in the client Smalltalk as the number of objects grows For this reason you should try to minimize faulting and fault in to the client only those objects that will actually be used in the client On the other hand inadequate faulting also has its penalties In the RPC version of GemBuilder communication overhead is important When fetching an employee object it is wasteful to stub the name and then immediately fetch the name from GemStone Even in the linked version it is better to avoid creating the stub and then invoking the fault mechanism when sending it a message Controlling the Fault Level By default two levels of objects are faulted with the linked version of GemBuilder and four levels are faulted for the RPC version This reflects the cost of remote procedure calls and the judgment that it is better to risk fetching unneeded objects to avoid extra calls to GemStone It is possible to tune the levels of stubbing to a more optimal level with a knowledge of the application being programmed You can set the configuration parameters faultLevelRpc and faultLevelLnk to a SmallInteger indicating 11 8 GemStone Systems Inc March 2006 Perfo
64. occasionally especially on Windows To avoid waiting forever in that case GBS double checks for a response every rpcSocketWaitTimeoutMs milliseconds stubDebugging When true stubs support debugging by responding to some basic messages locally such asprintOn instVarAt and class which returns GbxObjectStub When false these messages cause the stub to fault into the client image from GemStone traversalBufferSize Sets the size in bytes of the buffer used in traversal replication traversalCompression When true GemStone compresses the traversal buffer contents for transmission to the client and the client decompresses the traversal buffer contents upon receipt thus reducing the amount of data sent across a network connection to an RPC Gem If the network connection between the client and server transmits less than one million bits per second slower than a T1 line compression will probably improve transmission speeds assuming that the client and server machines are no slower than a 75 MHz 486 CPU verbose When true GemBuilder prints messages to the Transcript when certain events occur such as logging a session in or out or committing or aborting a transaction When false these messages are not printed The Settings Browser The Settings Browser makes it easy to examine and set the configuration parameters for GemBuilder In VisualWorks 7 x the Settings Browser is integrated with the client Smalltalk settings in VisualWo
65. read during your transaction while at the same time you have modified an object that the other session has read 3 It checks for locks set by other sessions that indicate the intention to modify objects that you have read or to read objects you have modified in your view If it finds no such conflicts GemStone commits the transaction and your work becomes part of the permanent shared repository Your view of the repository is refreshed and any new or modified objects that other users have recently committed become visible in any dictionaries that you share with them Read and Write Operations It is customary to consider the operations that take place within a transaction as reading or writing objects Any operation that accesses any instance variable of an object reads that object as do operations that fetch an object s size class or other descriptive information about that object An object also is read in the process of being stored into another object 7 10 GemStone Systems Inc March 2006 Managing Transactions Managing Concurrent Transactions An operation that stores a value in one of an object s instance variables writes the object While you can read without writing writing an object always implies reading it because GemStone must read the internal state of an object in order to store a value in it In order to detect conflict among concurrent users GemStone maintains two logical sets for each session a
66. repository Each Gem represents a single session An application can create more than one session each representing an internally consistent single view of the repository When a Gem commits a transaction it modifies the shared repository and updates its own view of the repository The Stone monitor process handles locking and controls concurrent access to objects in the repository ensuring integrity of the stored objects Each repository is monitored by a single Stone Despite its central role in coordinating the work of all individual Gems the Stone is surprisingly unintrusive To optimize throughput for all users most processing is handled by the Gems which often interact directly with the repository The Stone intervenes only when required to ensure the integrity of the multiuser repository 1 2 GemBuilder for Smalltalk GemBuilder for Smalltalk is a set of classes and primitives that can be installed in a Smalltalk image With the functionality provided by GemBuilder you can store your client Smalltalk application objects in the GemStone server import GemStone objects into client Smalltalk as client Smalltalk objects allow your application objects to be transparently replicated and maintained both in the client and in the server or allow some objects to reside only in the server but be accessible on the client arrange for messages sent to client Smalltalk objects to be forwarded and executed in the GemStone server by co
67. set containing objects read during a transaction and a set containing objects written These sets are called the read set and the write set Because writing implies reading the read set is always a superset of the write set The following conditions signal a possible concurrency conflict e An object in your write set is also in another transaction s write set a write write conflict e An object in your write set is in another transaction s read set and an object in your read set is in that transaction s write set a read write conflict Optimistic and Pessimistic Concurrency Control GemStone provides two approaches to managing concurrent transactions optimistic and pessimistic An application can use either or both approaches as needed Optimistic concurrency control means that you simply read and write objects as if you were the only session letting GemStone detect conflicts with other sessions only when you try to commit a transaction Pessimistic concurrency control means that you act as early as possible to prevent conflicts by explicitly requesting locks on objects before you modify them When an object is locked other users are unable to lock the object or commit changes to it Optimistic concurrency control is easy to implement in an application but you run the risk of having to re do the work you ve done if conflicts are detected and you re unable to commit When GemStone looks for conflicts only at commit time yo
68. shared objects for the application s use The application can perform computations retrieve objects and modify objects as though it were a single user Smalltalk image working with private objects When appropriate the application propagates its changes to the shared repository so those changes become visible to other users In order to maintain consistency in the repository GemBuilder encapsulates a session s operations computations fetches and modifications in units called transactions Any work done while operating in a transaction can be submitted to the object server for incorporation into the shared object repository This is called committing the transaction During the course of a logged in session an application can submit many transactions to the GemStone object server In a multiuser environment concurrency conflicts will arise that can cause some commit attempts to fail Aborting the transaction refreshes the session s view of the repository in preparation for further work In order to reduce its operating overhead a session can run outside a transaction but to do so the session must temporarily relinquish its ability to commit A session running outside a transaction operates in manual transaction mode in contrast to the system default automatic transaction mode Another potential mode is transactionless mode However this mode is not usable from within GemBuilder GemBuilder provides ways of avoiding the concurr
69. specify customized policies for translating between your client Smalltalk and GemStone server objects Chapter 6 describes GemBuilder s mechanisms for making your client Smalltalk objects persistent and Chapter 11 explains how to tune the system to minimize maintenance overhead and optimize performance GemStone s Smalltalk Language GemStone provides a version of Smalltalk that supports multiple concurrent users of the shared object repository through such features as session management reduced conflict collection classes querying transaction management and persistence GemStone Smalltalk is like single user client Smalltalk in both its organization and syntax Objects are defined by classes based on common structure and protocol and classes are organized into an is a hierarchy rooted at class Object The class hierarchy is extensible new classes can be added as required to model an application The behavior of common classes conforms to the ANSI standard for Smalltalk GemStone s class hierarchy is discussed in the introductory chapter to the GemStone Programming Guide The most significant difference between GemStone Smalltalk and client Smalltalk lies in GemStone s support for a multiuser environment in which persistent objects can be shared among many users As an object server GemStone must address the same key issues as conventional information storage systems that support multiple concurrent users For this reason Gem
70. system by adding it to the session s notify set Notify sets are virtual but persist through transactions living as long as the GemStone session in which they were created When the session ends the notify set is no longer in effect If you need it for your next session you must recreate it However you need not recreate it from one transaction to the next Class GbsSession provides the following two methods for adding objects to notifySets addToNotifySet adds one object to the notify set addAl1lToNotifySet adds the contents of a collection to the notify set When an object in the notify set appears in the write set of any committing transaction the system executes a previously defined client Smalltalk block sending a collection of the objects signaled as its argument By examining the argument the session can determine exactly which object triggered the signal March 2006 GemStone Systems Inc 7 17 Changed Object Notification GemBuilder User Manual Because these events are not initiated by your session but cause code to run within your session this code is run asynchronously in a separate Smalltalk process Depending on what else is occurring in your application at that time using this feature might introduce multi threading into your application requiring you to take some additional precautions See Multiprocess Applications on page 11 12 Example 7 2 demonstrates notification in GemBuilder Exam
71. system will be able to run with less overhead Switching Between Modes To find out if you are currently in a transaction execute aGbsSession inTransaction This returns true if you are in a transaction and false if you are not March 2006 GemStone Systems Inc 7 9 Managing Concurrent Transactions GemBuilder User Manual To change from manual to automatic transaction mode execute the expression aGbsSession transactionMode autoBegin This message automatically aborts the transaction if any changes the transaction mode and starts a new transaction To change from automatic to manual transaction mode execute the expression aGbsSession transactionMode manualBegin This message automatically aborts the current transaction and changes the transaction mode to manual It does not start a new transaction but it does provide a fresh view of the repository 7 5 Managing Concurrent Transactions When you tell GemStone to commit your transaction it checks to see if doing so presents a conflict with the activities of any other users 1 It checks to see whether other concurrent sessions have committed transactions of their own modifying an object that you have also modified during your transaction If they have then the resulting modified objects can be inconsistent with each other 2 It checks to see whether other concurrent sessions have committed transactions of their own modifying an object that you have
72. the image but not committed to the repository Mode Menu The Mode menu allows you to switch from dictionary mode to entry mode In dictionary mode you can select entries and dictionaries from the lists In entry mode you can edit or enter new text in the Symbol List and Selected Entry fields March 2006 GemStone Systems Inc 8 21 GemStone Administration Tools GemBuilder User Manual Edit Menu In Dictionary Mode the Edit menu allows you to rearrange dictionaries by cutting copying or pasting In Entry Mode the Edit menu allows you to rearrange entries by cutting copying or pasting Table 8 7 Edit Menu in the Symbol List Browser Cut Dict In Dictionary mode Removes the selected dictionary from the user s Cut Entry symbol list and places it in the session s clipboard In Entry mode Removes the selected entry from the selected Dictionary and places it in the session s clipboard Copy Dict Copies a reference to the selected item a dictionary or an entry Copy Entry depending which mode is in effect into the session s clipboard Paste Dict In Dictionary mode Causes the reference to the dictionary object in Paste Entry the clipboard to be added to the SymbolList in the pane with the name it had when it was put in the clipboard In Entry mode Causes the reference to the entry in the clipboard to be added to the selected dictionary with the name it had when it was put in the clipboard I
73. the more generic instruction GBSM logout This message prompts you with a list of currently logged in sessions from which to choose Before logging out GemBuilder prompts you to commit your changes if the GbsConfiguration setting confirm is true it is true by default If you log out after performing work and do not commit it to the permanent repository the uncommitted work you have done will be lost If you have been working in several sessions be sure to commit only those sessions whose changes you wish to save Session Management Using the Session Browser You can use the Session Browser to perform the same session management tasks that you can perform programmatically log in to the GemStone server view current sessions set the current session and log out of the GemStone server Logging In To log into the GemStone server with the Session Browser select the name of the session parameters object in the upper left pane and click on either Login Lnk or Login Rpc When you are logged in the Session Browser displays the session description in its lower pane If your login is not successful make sure you entered the correct parameters and that the necessary server processes are running 2 12 GemStone Systems Inc March 2006 Communicating with the GemStone Object Server Session Dependents Setting the Current Session The Session Browser s upper pane shows all of the known parameters that are regist
74. to make a client Smalltalk object persistent that is to store it in GemStone is to define a connector for the object A connector is an object that knows how to resolve a client Smalltalk object and a GemStone server object and how to establish a relationship between them when a session logs into GemStone Once you ve defined a connector for the two objects GemBuilder maintains the relationship between the shared GemStone server object and the private client Smalltalk object updating values from the repository to your application and vice versa as necessary The connector ensures that if a shared GemStone server object is modified the application s client Smalltalk counterpart is updated automatically Your client Smalltalk application updates shared objects in the repository by sending a commit message to a session With a successful commit changes to objects in the current session are propagated to the shared object repository in GemStone Once you have committed a transaction your application objects are updated with the most recently saved state of the repository incorporating changes made by other users GemStone Systems Inc March 2006 Basic Concepts GemBuilder for Smalltalk While for the most part GemBuilder will automatically manage objects in both the client Smalltalk and in the GemStone server you can exert as much control as you want over how objects are stored and used GemBuilder provides tools that let you
75. transactions and how to use them For further information see the chapter in the GemStone Programming Guide entitled Transactions and Concurrency Control Transaction Management an Overview introduces the concepts to be explained later in the chapter Operating Inside a Transaction explains the transaction model committing and aborting Operating Outside a Transaction discusses a lower overhead alternative for read only views of the shared repository Transaction Modes explains the difference between automatic and manual transaction modes Managing Concurrent Transactions discusses concurrency conflicts and ways to minimize them such as locks March 2006 GemStone Systems Inc 7 1 Transaction Management an Overview GemBuilder User Manual Reduced conflict Classes describes specialized GemStone collections that minimize conflicts without locking Changed Object Notification explains a mechanism for coordinating the activities of multiple sessions 7 1 Transaction Management an Overview The GemStone object server provides an environment in which many users can share the same persistent objects The object server maintains a central repository of shared objects When a GemBuilder application needs to view or modify shared objects it logs in to the GemStone object server starting a session as described in Chapter 2 A GemBuilder session creates a private view of the GemStone repository containing views of
76. tuning 11 8 when a stub receives a message 5 18 while flushing error caused by 5 28 faulting defined 5 10 faultLevelLnk configuration parameter A 2 A 5 faultLevelRpc configuration parameter A 2 faultToLevel 5 37 file writing class and method definitions to 3 18 file in and error handling 3 20 file out 10 8 file out methods 10 8 extents 1 3 filing out classes and methods 3 18 flushing 5 11 and committing compared 5 11 March 2006 GemStone Systems Inc Index 5 GemBuilder User Manual customized 5 27 5 31 improving performance of A 6 of dirty replicates 11 7 when 5 11 while faulting error caused by 5 28 flushing defined 5 10 forwarder 5 6 5 9 arguments to 5 8 classes that cannot become 6 6 converting 5 39 creating 5 7 creating interactively 6 19 debugging A 5 declaring in replication specification 5 7 defined 5 3 defunct 5 8 enforcing a return of 5 8 for optimization 11 11 return from 5 8 sending messages to 5 7 to client 5 6 to server 5 6 when to use 5 6 forwarderDebugging configuration parameter A 2 A 5 freeSlotsOnStubbing configuration parameter fwat 5 8 fwat ifAbsent 5 8 fwevaluate 5 37 fwevaluate context 5 38 G GbsBuffer 5 27 GbsClassInstVarConnector 6 10 GbsClassVarConnector 6 10 GbsConfiguration 4 10 GbsConnector 6 10 GbsError B 2 GbsFastConnector 6 10 GBSM global 2 7 GBSM instance of GbsSessionManager 2 5 7 4 GbsNameConnector 6 10 GbsR
77. up the signal receiving action GBSM currentSession sessionSignalAction giss nil gbsMessenger comment Signal 1 received from session 2 3 with giss signal with giss session with giss message Now from any session logged into the same Stone send a signal This example uses the same session GBSM currentSession sendSignal 15 to GBSM evaluate GsCurrentSession currentSession serialNumber withMessage This is the signal If the signal is received during GemStone execution the signal is processed and execution continues If aBlock is ni1 any previously installed signal action is deinstalled NOTE The method sessionSignalAction and the mechanism described above supersede the old mechanism that used the method gemSignalAction Do not use both this method and gemSignalAction during the same session only the last defined signal handler will remain in effect See the chapter entitled Error handling in your GemStone Programming Guide for details on using the error mechanism for change notification March 2006 GemStone Systems Inc 7 19 Changed Object Notification GemBuilder User Manual 7 20 GemStone Systems Inc March 2006 Chapter Security and Object Access Once objects have been successfully committed to GemStone they can be damaged or destroyed only by mishaps that damage or erase the disk files containing your repository GemStone provides several me
78. update its view of the GemStone user it shows The dialog will automatically be updated if the attached session aborts a transaction Close Close the dialog Changes are retained in the image but not committed to the repository The User menu contains one item Rename This requests a new name for this user You may not rename the DataCurator GcUser or SystemUser accounts The Help menu contains one item Session Info which provides information about the session for the GemStone User List and about the current session The Privileges Dialog Certain system functions are customarily performed by the DataCurator for example many of the messages to System require explicit privilege to use The privileges dialog displays the privileges an individual user possesses You can use this dialog to examine a user s privileges and if you have the authority to do so to select privileges for a user For more information on privileges see the chapter on Administering User accounts and Segments in the GemStone System Administration Guide The Privileges Dialog is shown in Figure 8 6 March 2006 GemStone Systems Inc 8 27 GemStone Administration Tools GemBuilder User Manual Figure 8 6 Privileges Dialog in GemStone User Window ruegos me CJ System Control O Statistics O Session Access CO User Password O Default Segment O Fed Admin Privilege CO Other Password J Segment Creation C Segment Pr
79. you may notice that most if not all of the dictionaries refer to themselves For example the dictionary named UserGlobals contains an Association for which the key is UserGlobals and the March 2006 GemStone Systems Inc 8 9 GemStone Administration Tools GemBuilder User Manual value is the dictionary itself Symbol list dictionaries define their own names so that you can refer to them conveniently in your own applications You can add the references to existing dictionaries or you may prefer to create a special purpose dictionary for each application adding the specialized dictionaries to symbol lists as needed Your system s authorization mechanism is probably set up to prohibit you from doing this yourself so you will probably need the cooperation of your GemStone data curator The GemStone System Administration Guide provides more information on this subject NOTE For performance reasons GbsSession uses a transient copies of your symbol list If you change this transient copy programmatically the changes are not immediately reflected in the permanent GemStone object Also changes to the permanent GemStone symbol list are not reflected in the GbsSession s transient symbol list until a transaction boundary If you must be absolutely certain that the two copies are synchronized log out and log back in again For a complete discussion of symbol resolution and object sharing see the relevant chapters of the GemStone
80. 1 Schema Modification Client Smalltalk and GemStone Smalltalk both have schema modification support Client Smalltalk supports only a single instance of a class when a class is modified instance migration occurs immediately Because GemStone stores persistent objects schema modification is a more complex issue GemStone Smalltalk supports schema modification and protects the integrity of your stored data by allowing you to define different versions of classes It keeps track of these versions in a class history object Every class in GemStone Smalltalk has a class history instance variable A class history is an object that maintains a list of all versions of the class Every GemStone class is listed in exactly one class history You can define any number of different versions of a class and declare that the different versions belong to the same class history You can also migrate some or all instances of one version of a class to another version when you need to By default migration of an object from one class version to another will preserve the values of unnamed instance variables and instance variables that have the same name in both classes It is not necessary for different versions of a class to have a similar structure or a similar implementation The classes don t even need to have the same name although it is probably less confusing if they do or if you establish and adhere to some naming convention The section entitled Modi
81. 2 programmatically 2 10 logging out of GemStone effect on locks 7 14 interactively 2 13 programmatically 2 12 to resynchronize application state 7 8 login authorization 8 2 faulting at 5 18 login message 2 10 logout message 2 12 lost OT root 7 8 main statistics 11 3 makeGSTransparent 5 13 managing concurrent transactions 7 10 connectors 6 12 space and cache size 11 10 manual mark dirty 5 14 manual transaction mode 7 9 manual organization of 1 iv mapping 5 3 automatic 5 5 class 1 4 class versions and 5 6 classes 5 3 classes with different storage formats 5 31 instance variables 5 15 nonmatching names 5 16 schema coordination 10 6 mark dirty 5 11 5 14 markDirtyOnAtPut 5 13 markDirtyOnInstvarAssign 5 13 marking dirty automatic in VisualWorks 5i 5 12 in VisualWorks 7 x 5 11 marking dirty manually 5 14 maximum number of instance variables in a class 3 12 messages faulting when a stub receives 5 18 Method Categories pane in GemStone Browser 3 5 methods breakpoints in 4 2 filing out 3 18 primitive and breakpoints 4 7 protecting 8 2 public 3 17 special and breakpoints 4 7 without step points 4 7 migration authorization errors and 10 4 destination 10 3 ignoring 10 4 instance variable mapping 10 4 methods for migrate Object 10 3 migrateFrom instVarMap Object 10 5 migrateInstances to Object 10 4 migrateTo Object 10 3 of instances 10 2 monitoring GemStone execution 11 2 m
82. 2 3 The Session Parameters Editor o o 2 9 Figure 2 4 Committing with Approval From a Session Dependent 2 17 Figure 3 1 GemStone Classes Browser o oo e 3 4 Figure 3 2 GemStone System Workspace o o ooo oo o 3 10 Figure 4 1 GemStone inspector o ooo 4 2 Figure 4 2 GemStone Inspector GS Delegate tab o 4 3 Figure 4 3 Inspector ona Replicate o ooo oo o 4 4 Figure 4 4 Evaluating self in the GS Delegate tab of the Inspector 4 5 Figure 4 5 GemStone Breakpoint Browser with a Breakpoint 4 9 Figure 5 1 Two level Fault of an Object o ooo oo 5 18 Figure 5 2 A Stub Responds to a Message oo o e 5 19 Figure 6 1 Connecting Application Roots o ooo o 6 3 Figure 6 2 Root Objects s ec gb bi ee nap raa pap ee a 6 4 Figure 6 3 Connecting a Name Connector o oo e 6 9 Figure 6 4 Connector Class Hierarchy o o ooo o 6 10 March 2006 GemStone Systems Inc xix GemBuilder User Manual Figure 6 5 The Connector Browser 6 0 00 00 000 eee 6 16 Figure 7 1 GemBuilder Application Workspace oo 7 3 Figure 8 1 GemStone s Object Level Security Mechanism 8 5 Figure 8 2 The Segment Tool o o ooo oo 8 11 Figure 8 3 The Symbol List Browser o oo 8 20 Figure 8 4 GemS
83. 3 3 Browsing Code GemBuilder User Manual 3 2 Browsing Code After logging in to GemStone open a GemStone Classes Browser by choosing GemStone gt Browse gt All Classes The GemStone Classes Browser allows you access source and other information about each of the kernel classes and methods you can also create GemStone Smalltalk classes and methods in the GemStone repository Figure 3 1 GemStone Classes Browser Symbol dictionaries Method categories Classes Method selectors y 6 O x UserGlobals Accessing A associationsDo Globals Addin keysAndAssociatior Published identtyindex EE CovererVareesyt UserClasses IdentityKeyValueDi Hashing IdentitySet Locking Support IndexDictionaryEnti y Private instance class Ramoving v keysAndValuesDo aBlock A Evaluates aBlock with each of the receiver s key value pairs as the arguments The argument aBlock must be a two argument block The first argument is the key and the second argument is the value of each key value pair Returns the receiver Reimplemented to send value to each Association Source code pane aKey collisionBkt 1 to tableSize 2 by 2 do tablelndex nil aKey self _at tablelndex ifTrue a The GemStone Classes Browser is similar to the client Smalltalk System or Classes Browser but a few differences exist for example the upper left pane contains a list of symbol dictionaries
84. 5 12 GemStone Systems Inc March 2006 Sharing Objects Replicates piece of code the markDirty message will be sent multiple times when only one is actually needed To enable automatic dirty marking for a class s named instance variables send the client Smalltalk class the message markDirtyOnInstvarAssign To disable it send removeMarkDirtyOnInstvarAssign To enable automatic dirty marking for a class s indexable instance variables send the client Smalltalk class the message markDirtyOnAtPut To disable it send removeMarkDirtyOnAt Put markDirtyOnAtPut is more expensive than markDirtyOnInstvarAssign To enable both mechanisms send makeGsTransparent To remove all dirty marking mechanisms send removeMakeGSTransparent Sending a class markDirtyOnInstvarAssign modifies instance variable assignments in methods of the receiver and all its subclasses Superclasses are not modified For example superclass A defines instance variable a Its subclass B inherits a and defines instance variable b Bis sent markDirtyOnInstvarAssign If an instance of B receives a message for which the method is inherited from A the instance won t get marked dirty when the inherited method modifies instance variable a You can correct the situation in either of two ways e You can enable automatic dirty management on the superclass A Of course this affects instances of A as well a
85. 6 Contents Chapter 1 Basic Concepts 1 1 The GemStone Object Server o o o ee 1 2 1 2 GemBuilder for Smalltalk 1 3 The Programming Interface aoaaa ee 1 4 Transparent Access to GemStone o oo o 1 4 GemStone s Smalltalk Language o ooo 1 5 The GemBuilder Tools 1 6 1 3 Designing a GemStone Application an Overview 1 7 Which objects should be stored and shared 1 7 Which objects should be secured 2 2 2 eee eee 1 8 Which objects should be connected o o ooo ooo 1 8 How should transactions be handled 1 9 How can performance be improved 0 0 1 9 1 4 Delivery and Deployment o ooo ooo e 1 9 Public and Private Classes and Methods 1 10 March 2006 GemStone Systems Inc xi GemBuilder User Manual Chapter 2 Communicating with the GemStone Object Server 2 iC lent Apane na eke da ead WAR Rs A Be ea 2 2 2 2 GeMStONne SESSIONSiss e rr ga oe a hae a a a eee ee gerne 2 2 RPC and Linked Sessions 0 ee ee 2 3 2 3 Session Control in GemBuilder 2 4 Defining Session Parameters o o o ooo 00000008 2 5 Defining Session Parameters Programmatically 2 6 2 4 The GemStone Session Browser o 2 8 Starting the Session Browser o ooo o 2 8
86. For example suppose the value returned from sending replicationSpec to the subclass is mame min 1 name max 2 The last occurrence of the instance variable is max 2 and therefore takes precedence If subclass implementations of replicationSpec always append their results to super replicationSpec the subclass will reliably override the superclass handling of a given instance variable The recommended approach is super replicationSpec name max 2 not name max 2 super replicationSpec Another apparent contradiction can arise between parent and child objects For example suppose Employee refers to an Address which refers to a complex object County The Employee replicationSpec includes address min 5 specifying that several levels of the County object are to be replicated But if 5 26 GemStone Systems Inc March 2006 Sharing Objects Replicates Address includes county max 1 it modifies Employee s handling of address Employee specifies Get at least 5 levels of address Address specifies Whatever you do don t get more than one level of county The apparent contradiction is resolved by the order in which these specifications are encountered because Address is encountered after Employee Address takes precedence If your object network includes cycles different replication specs could take effect at different times depending on which object is the replication root a
87. Managing Concurrent Transactions 2 ooo o e 7 10 Read and Write Operations o oo oo 7 10 Optimistic and Pessimistic Concurrency Control 7 11 Setting the Concurrency Mode ooo ooo o 7 12 Setting LOCKS s e eae ae a A a 7 13 Releasing Locks Upon Aborting or Committing 7 15 7 6 Reduced conflict Classes 2 ee 7 16 7 7 Changed Object Notification 2 0 0 eee ee ee 7 17 Gem to Gem Notification 2 0 0 0 00 a 7 18 Chapter 8 Security and Object Access 8 1 Object Level Security eee 8 2 Requiring Login Authorization o o o 8 2 Controlling Visibility of Objects o ooo 8 2 Protecting Methods o oo e 8 2 Using GemStone s Authorization Mechanisms 8 3 8 2 Classes for Controlling Access to Objects 2 2 2 ee ee 8 4 Repository auc do ok ad es BOE EE a AAA 8 4 Segmente sai To ted sensed Rt A Bok Mea ly dd 8 4 UserProfil asus ete Sede ea eens ed tbe dees A 8 5 8 3 Sharing Access to Objects ee 8 6 Group Authorization and Object sharing 8 7 March 2006 GemStone Systems Inc xv GemBuilder User Manual Using Segments for Authorization 8 7 Making Objects Accessible Through Symbol Lists 8 9 8 4 GemStone Administration Tools 8 10 The Segment Looks a Boh Os oe Un bot coo Oe he Ba 8 11
88. Name gsName gsName The above methods require that the server object already exist If GemBuilder must create the object choose an instance creation method that specifies the GemStone server dictionary in which to place it GbsNameConnector stName stName gsName gsName dictionaryName gsDictionary To create a class variable connectors GbsClassVarConnector stName ClassName gsName ClassName cvarName ClassVarName Similarly a class instance variable connector GbsClassInstVarConnector stName ClassName gsName ClassName cvarName ClassInstVarName For more browse instance creation methods for each connector class Setting the Postconnect Action The symbolic names for postconnect actions are updateST updateGs tforwarder clientForwarder and none All connectors default to using updateST except class connectors which default to none To cause a GemStone server object to take its initial values at login from its Smalltalk counterpart send postConnectAction updateGs to the connector This is occasionally useful for loading data into GemStone from the client image March 2006 GemStone Systems Inc 6 11 Making and Managing Connectors GemBuilder User Manual Adding Connectors to a Connector List When you create a connector you must decide whether it is to be managed by an individual session or globally Leaving it unmanaged can have several adverse effects it will not be connected and disc
89. Programming Guide 8 4 GemStone Administration Tools The following sections describe the GemStone tools that are provided to allow you to easily manage the object sharing and protection issues discussed in the previous section e The Segment Tool is a tool for examining and changing GemStone user authorization e The Symbol List Browser is a tool you can use for examining the GemStone SymbolLists associated with UserProfiles You can use it to add and delete dictionaries from these lists as well as to add delete and inspect the entries in the dictionaries e The User Account Management Tools are a set of three tools the User List the User Dialog and the Privileges Dialog that allow you to create new user accounts change account passwords and assign group memberships 8 10 GemStone Systems Inc March 2006 Security and Object Access GemStone Administration Tools The Segment Tool The Segment Tool allows you to inspect and change the authorization that GemStone users have at the object level As explained in the section entitled Group Authorization and Object sharing beginning on page 8 7 each object in GemStone is assigned separately to a segment The only users authorized to read or modify an object are those who are granted read or write authorization by the segment it is assigned to The Segment Tool also allows you to examine and change group membership Some of the operations supported by the Segment To
90. Requests aConnector postConnectAction forwarder aParams addConnector GbsClassVarConnector stName GST_Company gsName GST_Company cvarName AllCompanies You can create methods similar to those shown in examples 6 5 and 6 6 to create name connectors and global connectors for your application as well NOTE If more than one session is logged into GemStone using the same session parameters object and you add a connector to one of those sessions March 2006 GemStone Systems Inc 6 15 Making and Managing Connectors GemBuilder User Manual GemBuilder will try to connect that connector for all sessions sharing the same parameters If any fail to reference the GemStone server object represented by the connector you ll receive an error message stating that the connector failed to connect The Connector Browser You can use GemBuilder s Connector Browser to make and manage connectors interactively To open a Connector Browser select Connectors from the GemStone menu With this browser you can e examine create and remove global or session based connectors e inspect the client or server object to which a connector resolves e determine whether a specified connection is currently connected e connector disconnect a connector and e examine or modify the postconnect action associated with a connector Figure 6 5 shows the Connector Browser Figure 6 5 The Connector Browser S
91. Segment Definition Area o o oo ooo eee 8 12 Group Definition Area o o ooo ooo o 8 13 Segment Tool Menus o ooo ooo 8 14 Using the Segment Tool o o o o oo ooo 8 17 The Symbol List Browser o o o 8 20 The Clipboard pegea ema ras ata 8 21 Symbol List Browser Menus o oo 8 21 User Account Management Tools o ooo 8 23 GemStone User List o ee ee 8 23 GemStone User Dialog o o o 8 25 The Privileges Dialog o oo oo 8 27 Chapter 9 Exception Handling 9 1 GemStone Errors and Exception Classes o ooo 9 1 9 2 Handling Exceptions o ooo eo 9 3 User defined ErrOrS e 9 4 9 3 Interrupting GemStone Execution o ooo oo e 9 6 Chapter 10 Schema Modification and Coordination 10 1 Schema Modification e ee 10 2 Instance Migration Within GemStone o o o ooo co 10 2 Setting the Migration Destination 10 3 Migrating Objects 2 aa en 10 3 Things to Watch Out For 2 2 ee eee 10 4 Instance Variable Mapping in Migration 10 4 10 2 Schema Coordination 2 2 ee 10 6 10 3 The Class Version Browser 10 7 Menus in the Class Version Browser 10 7 Chapter 11 Performance Tuning 1151 PronlinSs i oo ra tt ai ek eee le oe e olan ib 11 2 xvi GemStone
92. SmallInteger jobTitle must be an instance of String department must be an instance of Symbol and address must be an instance of Address instancesInvariant false When instances of the class are created their values will be modifiable even after they ve been committed to the repository isModifiable true This class is modifiable instance variables can still be added removed and constrained and class or class instance variables can be added However as long as the class itself remains modifiable no instances of it can be created Subclass Creation Methods You can choose from a variety of subclass creation messages depending on the type of class you want to create For example to create a byte subclass replace the initial keyword subclass with the keyword byteSubclass Ifthe 3 14 GemStone Systems Inc March 2006 Using the GemStone Programming Tools Coding superclass is not a subclass of String instances of the new class store and return SmallIntegers in the range 0 255 Similarly if you wish to create an indexable subclass replace the initial keyword subclass with the keyword indexableSubclass Instances of the new class are represented as pointer objects For complete descriptions of the different kinds of classes see the discussion of class storage formats in the chapter entitled Advanced Class Protocol in the GemStone Programming Guide If you wish to set the class history of your ne
93. Stone s Authorization Mechanisms The easiest and most reliable way to secure objects however is to use GemStone s authorization and privilege mechanisms Segments GemStone s authorization mechanism uses a class called Segment to protect objects from access by users who have not been explicitly given permission to use them Every user can use the authorization mechanism to protect both data and code objects selectively Segment objects have an owner and settings for read and write access for the owner groups of users and everyone else When someone tries to read or write an object that references a segment to which he or she lacks the proper access GemStone raises an authorization error and does not permit the requested operation Segments are not meant to organize objects for retrieval GemStone uses Symbol Lists for that Moreover segments don t have any relationship to the physical location of objects on disk they are merely security objects Segments are discussed in more detail in subsequent sections GemStone Administration Tools on page 8 10 and The Segment Tool on page 8 11 Privileges A few GemStone Smalltalk methods can be executed only by those who have explicitly been given the necessary privileges The privilege mechanism is entirely independent of the authorization mechanism This mechanism allows the system administrator to control who can send certain powerful messages such as those that halt
94. Stone s Smalltalk includes classes for e managing concurrent access to information e protecting information from unauthorized access and e keeping stored information secure and restoring it in the event of a failure You should be aware of a few differences between GemStone Smalltalk and client Smalltalk in syntax and in the behavior of some of the classes A summary of these differences can be found in Appendix D March 2006 GemStone Systems Inc 1 5 GemBuilder for Smalltalk GemBuilder User Manual The GemBuilder Tools GemBuilder s programming environment provides tools for programming in GemStone Smalltalk The following tools are described in detail in subsequent chapters of this manual A GemStone System Browser lets you examine modify and create GemStone classes and methods A GemStone System Workspace provides easy access to commonly used GemStone Smalltalk expressions GemStone Inspectors let you examine and modify the state of GemStone objects A GemStone Breakpoint Browser and a Debugger let you examine and dynamically modify the state of a running GemStone application A Session Browser allows you to manage sessions and transactions A Connector Browser allows you to manage the connectors that establish relationships between client Smalltalk and GemStone server objects A Class Version Browser can be used for examining a class history inspecting instances migrating instances deleting versions
95. Stone error dictionaries and how to handle GemStone errors predefined and user defined within the GemStone environment see the chapter entitled Handling Errors in the GemStone Programming Guide For more information about defining error handlers in the client Smalltalk refer to your client Smalltalk documentation on exception handling March 2006 GemStone Systems Inc 9 5 Interrupting GemStone Execution GemBuilder User Manual 9 3 Interrupting GemStone Execution When executing GemStone server Smalltalk in a non blocking RPC session it s possible to interrupt GemStone execution by sending the session softBreak GemStone responds by raising GbsRtErrSoftBreak which is a continuable exception GBS automatically sends softBreak when a client Smalltalk user interrupt occurs in a Process executing GemStone server code in a non blocking RPC session If VisualWorks can t determine which Process to interrupt when control Y is entered try executing GBSM softBreak or aGbsSession softBreak if you have more than one GemStone session In addition to being continuable soft break can also be handled on the server by an exception handler There is another mechanism called hard break which is not continuable and cannot be handled on the server Sending an executing GbsSession the message hardBreak stops server execution aborts the current GemStone transaction and raises GbsRtErrHardBreak on the client In GBS in situati
96. Stone server Or if a class implements both inst VarMap and replicationSpec the instVarMap determines which instance variables will be visible to the replication spec e Inthe absence of a replication spec the instance method fault ToLevel if called is respected for replicates Forwarders of course do not fault e For classes that use no other mechanism the configuration parameters faultLevelLnk and faultLevelRpc are respected 5 6 Evaluating Smalltalk Code on the GemStone server In addition to sending messages to forwarders GemBuilder provides mechanisms to execute ad hoc Smalltalk code on the server Using the development environment Workspace you can type in and select Smalltalk code and use the menu option GS Do it GS Inspect it or GS Print it to execute the selected text on the GemStone server and return a replicate of the results You can also do this on the client by sending the string to a session for execution The expression aGbsSession evaluate aString when executed on the client tells GemBuilder to have the server compile and execute the GemStone Smalltalk code contained in aString and answer a client replicate of the result of that execution If rather than a replicate you would like the result as a forwarder use the expression aGbsSession fwevaluate aString The code in aString may be any arbitrary GemStone Smalltalk code that would compose a valid method body see appendix A
97. The GemBuilder for Smalltalk Tutorial provides an introduction to programming GemStone applications with GemBuilder March 2006 GemStone Systems Inc vV GemBuilder User Manual A description of the behavior of each GemStone kernel class is available in the class comments in the GemStone Smalltalk repository In addition if you will be acting as a system administrator or developing software for someone else who must play this role you will need to read the GemStone System Administration Guide vi GemStone Systems Inc March 2006 Technical Support GemStone provides several sources for product information and support The product specific manuals and online help provide extensive documentation and should always be your first source of information GemStone Technical Support engineers will refer you to these documents when applicable GemStone Web Site http support gemstone com GemStone s Technical Support website provides a variety of resources to help you use GemStone products Use of this site requires an account but registration is free of charge To get an account just complete the Registration Form found in the same location You ll be able to access the site as soon as you submit the web form The following types of information are provided at this web site Help Request allows designated support contacts to submit new requests for technical assistance and to review or update previous request
98. Works 7 0 Object Engine to detect modifications to replicates on the client so that modified replicates can be automatically marked dirty This mechanism is fast reliable and does not affect client objects that are not replicates Thus when using VisualWorks 7 x we recommend always using automatic dirty marking Automatic dirty marking is enabled by default To disable automatic dirty marking execute GbsConfiguration current autoMarkDirty false March 2006 GemStone Systems Inc 5 11 Replicates GemBuilder User Manual or use the Settings Tool to turn off the configuration parameter autoMarkDirty It is enabled or disabled globally for the client you cannot enable automatic dirty marking for only some classes or objects in the client virtual machine If you disable automatic dirty marking your application must mark modified client replicates dirty as described in Marking Modified Objects Dirty Manually on page 5 14 Marking Modified Objects Dirty Automatically in VW 5i Because The VisualWorks 5i Object Engine lacks the features needed to implement fully automatic detection of modification to replicates GemBuilder uses a different automatic dirty marking mechanism in VisualWorks 5i The configuration parameter autoMarkDirty has no effect in VisualWorks 5i Automatic dirty marking in VisualWorks 5i must be explicitly enabled by the application developer for each class and slows operations on all instances of e
99. able A 2 VW7 Settings Browser Categorization Connectors connectorNilling connectVerification removelnvalidConnectors Debugging assertionChecks deprecationWarnings forwarderDebugging stubDebugging Replication autoMarkDirty blockReplicationEnabled blockReplicationPolicy defaultFaultPolicy faultLevelLnk faultLevelRpc freeSlotsOnStubbing Server Communication blockingProtocolRpc libraryName pollForRpcResponse rpcSocketWaitTimeoutMs traversalBufferSize traversalCompression Signals And Events eventPollingFrequency eventPriority pollForAsynchronousEvents User Interface alwaysUseGemCursor confirm verbose The VisualWorks 7 x Settings Browser has the following buttons Table A 3 Buttons in the VW7 Settings Browser Apply Default Settings Reset all GemStone settings to their default value OK Close the Settings Browser applying all changes to the current configuration Cancel Close the Settings Browser cancelling all unapplied changes A 10 GemStone Systems Inc March 2006 Configuring GemBuilder Table A 3 Buttons in the VW7 Settings Browser Apply Apply all unapplied changes to the current configuration Help Open a dialog with help for the configurations on the current view The VisualWorks 5i Settings Browser Figure A 2 The VW5i Settings Browser Summary GemBuilder Settings loj xj Parameters ge
100. ach class for which it is enabled Although we generally recommend using VisualWorks 5i automatic dirty marking over manual dirty marking there are some cases where manual dirty marking can improve performance If you choose to let GemBuilder mark client Smalltalk objects dirty automatically you can choose to mark objects dirty when you assign values to e named instance variables e indexed instance variables or e in both of these situations GemBuilder handles dirty marking on a class basis you can enable automatic dirty management for some classes while disabling it for others When you enable dirty marking for a class GemBuilder changes its default compiler tosend self markDirty after every instance variable assignment and after every at put and basicAt put In this way GemBuilder detects changes to all named and indexable variables You won t see these extra message sends by examining your source code but you can see them by looking at the decompiled version of a method in a browser To do so hold down the Shift key while selecting the method selector While debugging you ll see the cursor jump to the top left of the code pane when stepping past such an embedded markDirty message Since the automatic markDirty mechanism in VisualWorks 5i relies on message sends inserted by the compiler there are likely to be unnecessary message sends in your application For example if you modify several instance variables in a
101. ains the difference between RPC and linked sessions Session Control in GemBuilder explains how to use the classes GbsSession GbsSessionManager and GbsSessionParameters to manage GemBuilder sessions The GemStone Session Browser describes the GemStone Session Browser March 2006 GemStone Systems Inc 2 1 Client Libraries GemBuilder User Manual Logging In To and Logging Out Of GemStone describes how to log in and out of GemStone sessions programmatically and using the Session Browser Session Dependents explains how to use the Smalltalk dependency mechanism to coordinate the effects of session management actions on multiple application components 2 1 Client Libraries Before you can log in to a GemStone object server in addition to having GBS loaded in your image you must have the client libraries available for loading into your image The client libraries are provided with the GemStone object server product release You must use the correct client libraries for the particular version of the object server you wish to connect to and for the platform that the client Smalltalk image is running on If you update to a new version of GBS but continue to use the same version of the GemStone server the same clientLibraries will be used The client libraries must be on the platform dependent search path To set the client library use the GbsConfiguration setting LibraryName You may also execute GbsConfiguration cur
102. alltalk worlds meet The contexts below this point are client Smalltalk contexts Like other GemBuilder text areas the debugger source code pane provides commands to execute GemStone Smalltalk and it lets you examine step points and set breakpoints Getting a Stack Trace Without a Debugger In a situation in which you encounter an error but cannot use the Smalltalk debugger such as in a runtime application or when the result is a virtual machine crash you can write a stack trace to a text file To do so execute GbsConfiguration dumpAllProcessStacks In response all processes in the image write their contexts to a file named stacksAtx txt in the current working directory where x is a 10 digit number derived from a time stamp 4 10 GemStone Systems Inc March 2006 Chapter Sharing Objects This chapter describes how GemBuilder shares objects with the GemStone S object repository Which Objects to Share is an overview of the process of determining how to make good use of GemBuilder s resources and introducing forwarders and replicates and stubs Class Mapping explains how classes are defined and how forwarders stubs and replicates depend on them Forwarders explains how to use forwarders to store all an object s state and behavior in one object space Replicates explains replicating GemStone server objects in client Smalltalk or vice versa describes the processes of propagating changes t
103. ally mark a replicate dirty send markDirty to the replicate immediately after each time your application modifies it If a replicate is modified on the client but not marked dirty the modification will be lost eventually The object could be overwritten with its GemStone server state after the application has executed code on the server or at the next transaction boundary Even if the client object is never overwritten the modification will never be sent to the server Minimizing Replication Cost Replicating the full state of a large and complex collection can demand too much memory or network bandwidth Optimize your application by controlling the degree and timing of replication GemBuilder provides three ways to help Instance Variable Mapping Modify the default class map to specify how widely through each object to replicate which instance variables to connect and which to prune as never being of interest in the other object space You can also specify the details of an association between two classes whose structures do not match 5 14 GemStone Systems Inc March 2006 Sharing Objects Replicates Stubbing Specify how deeply through the network to replicate how many layers of references to follow when faulting occurs Replication Specifications Another way to specify how widely or deeply through each object to replicate of a class s mapped instance variables which to replicate and which to stub Inst
104. an t modify write them or add new ones e write means that a user can read and modify any of the segment s objects and create new objects associated with the segment e none means that a user can neither read nor write any of the segment s objects NOTE Be careful when changing the authorizations on any segment that a user may be using as a current segment or a default segment Group Definition Area The bottom of the dialog is the group definition area In this area you can assign authorizations to groups of users instead of individuals Groups are typically organized as categories of users who have common interests or needs When you select a segment at the top of the dialog the group definition area displays the groups that have access to the segment When you select one of the groups its members appear In the group definition area you can change the following Group Name You can change the group name but you should be aware that when you edit a group name you are not just renaming the group you are actually replacing the group with a new one The old group s members are not copied to the new one so you need to add them again If the name of the group entered is a group that does not exist you will be asked if you want to create it Group Access Group access can be changed in the same way as owner and world access To change group access type either read or write into the cell as outlined for owner and world acce
105. ance Variable Mapping As discussed in Class Mapping on page 5 3 before GemBuilder can replicate objects it must know their respective structures and the mapping between them By default GemBuilder maps instance variables by name You can override this default either by suppressing the copying of certain instance variables or by explicitly specifying a mapping between nonmatching names Suppressing Instance Variables Some client Smalltalk objects must define instance variables that are relevant only in the client environment for example a reference to a window object Such data is transient and doesn t need to be visible to the GemStone server Situations can also arise in which the server class defines instance variables that a given application will never need many applications can share repository objects without necessarily sharing the same concerns Mapping allows your application to prune parts of an object Suppress the replication of an individual instance variable simply by omitting its name from its counterpart s class definition e Jfa client object contains a named instance variable that does not exist in its GemStone server counterpart the value of that variable is not replicated in the server When GemBuilder faults the server object into the client the client s suppressed instance variable remains unchanged e Likewise if a server object contains a named instance variable that does not exist in its client co
106. ances of Class X Versions 1 or 3 the replication spec will not affect them March 2006 GemStone Systems Inc 5 23 Replicates GemBuilder User Manual Multiple Replication Specifications It s not always possible to define one replication spec that works well for all operations in an application Some queries or windows may require a different object profile than others in the same application and session a replication spec crafted to optimize one set of operations can make others inefficient By default the message replicationSpec returns the default replication spec Change this by sending the message replicationSpecSet someRepSpecSelector to an instance of GbsSession With this message you can specify multiple replication specs selecting one dynamically according to circumstances The following procedure shows how Step 1 Decide on a new name such as replicationSpec2 Step 2 Implement Object class gt gt replicationSpec2 to return self replicationSpec Step 3 Reimplement replicationSpec2 as appropriate in those application classes that need it Step 4 Immediately before your application performs the query or screen fetch or other operation that requires the second replication spec send replicationSpecSet replicationSpec2 to the current GbsSession instance For example suppose your application has a class Employee with instance variables firstName lastName and address address contains an instan
107. anged during some server operations by the GBS tools assertionChecks This parameter is for the use of GemStone customer support autoMarkDirty Defines whether modifications to client objects are automatically detected When false the application must explicitly send markDirty to a client object after it has been modified so GemBuilder will know to update the object in GemStone This parameter is not available under VisualWorks 5i blockingProtocolRpc Determines whether to use blocking or nonblocking protocol for RPC sessions When false nonblocking protocol is used enabling other processes to execute in the image while one or more processes are waiting for a GemStone call to complete When true GemBuilder must wait for a GemStone call to complete before proceeding with the execution process that called it blockReplicationEnabled When false GemBuilder raises an exception when block replication is March 2006 GemStone Systems Inc A 3 GemBuilder User Manual attempted useful in determining if your application depends on block replication blockReplicationPolicy Legal values are replicate or callback Block replication requires decompiling and compiling the source code for blocks at runtime which sometimes can cause problems due to limitations on block replication it is usually not possible to include the Smalltalk compiler in a runtime image Block callbacks use client forwarders to evaluate the block in the
108. arest the cursor location If the cursor is not exactly at a step point scans the method from the current cursor location on and sets a breakpoint at the next step point See Debugging on page 4 1 for a full discussion of using breakpoints 3 8 GemStone Systems Inc March 2006 Using the GemStone Programming Tools The System Workspace GemBuilder also adds the following items to the appropriate menus in the client Smalltalk browsers Table 3 5 Additional GemStone Menu Items create in GS Creates a GemStone Smalltalk class having the same name and structure as the selected client Smalltalk class if one doesn t already exist If it does exist but you ve changed its structure executing this menu item creates a new version of the class compile in GS Creates a GemStone Smalltalk class having the same name and structure as the selected client Smalltalk class and compiles all currently defined methods for the class in GemStone If necessary a notifier lists any methods that cannot be compiled 3 3 The System Workspace The GemStone System Workspace is a workspace containing templates for many useful GemStone Smalltalk and client Smalltalk expressions Browse it to familiarize yourself with its contents To open a GemStone System Workspace Figure 3 2 choose GemStone gt Tools gt System Workspace from the GemStone menu March 2006 GemStone Systems Inc 3 9 Coding GemBuilder User Manual Figure 3
109. at is mapped to an old version of a GemStone server class a version that is not the migration destination will be logged to the transcript If you see this happening frequently you should consider 10 6 GemStone Systems Inc March 2006 Schema Modification and Coordination The Class Version Browser migrating your instances to the GemStone server class version corresponding to your client Smalltalk class 10 3 The Class Version Browser The Class Version Browser is a specialized Class Browser that can be used for examining a class history inspecting instances migrating instances deleting versions and moving versions to another class history To open a Class Version Browser select a class in a browser and choose Browse Versions from the Classes menu If more than one version of a class has been created the class list in the spawned browser displays the version number next to the class name A Class Version Browser is shown in Figure 10 1 Figure 10 1 The Class Version Browser GemStone Class Version Browser for MusicCollection on Sessio MusicCollection 1 instance class Accessing Updating classVars classinstVars poolDictionaries inDictionary UserClasses constraints the elements MusicRecording instancesInvariant false isModifiable false Bag subclass MusicCollection instVarNames owner Menus in the Class V
110. at you can find out what the system was doing at the time a breakpoint or an error interrupted execution e You can execute a message expression within the scope of a given context 4 2 Inspectors To allow you to examine the values of GemStone server objects and modify them when appropriate GemBuilder provides inspectors that are similar to the client Smalltalk inspectors When you select a GemStone Smalltalk expression and execute GS Inspect it a GemStone inspector opens as in Figure 4 1 Figure 4 1 GemStone inspector l0x Object Edit Go History Explore Tools Help EAS El GS Elements GS Basic GS Delegate GS Methods j anArray aaa bbb 23 The GemStone inspector provides three or more tabs depending on the specific object you are inspecting each with the GS prefix to indicate that these apply to a GemStone server object The GemStone inspector also allows you to examine the internal state of the object s delegate in GemBuilder by selecting the tab labeled GS Delegate GemStone Systems Inc March 2006 Debugging Inspectors Figure 4 2 GemStone Inspector GS Delegate tab Y an Array AE ES Object Edit Go History Explore Tools Help lt gt e 88 8 3 amp GS GS Elements GS Basic GS Delegate GbsObject oopValue 133181 gsOop sessionld 2 active aa isStDirty is false se isROM Object is false isSpecial isDefunct isSkew is false c
111. ated with a group any user whose UserProfile also includes that group has the right to read from your default segment Note that you cannot always add group authorizations for a segment you own and you might need to ask your data curator or system administrator for help in adding authorization for a new group Using Segments for Authorization As explained in the previous section segments define authorization attributes for all the objects assigned to them All objects assigned to a given segment have the same protection if you can read or write one object assigned to a segment you can read or write all of them Each segment is owned by one user and that user authorizes read access write access or no access at all to objects assigned to that segment for the owner a number of named groups of users and the world that is all users of that GemStone repository March 2006 GemStone Systems Inc 8 7 Sharing Access to Objects GemBuilder User Manual A segment can be used to provide or restrict access to objects that are associated with it Segments are merely authorization objects they are not storage locations Whenever you create an object it is associated with a Segment and the characteristics of the segment determine who has access to that object Each segment has a single owner who can determine the level of access that the various groups of GemStone users have to that segment and to the objects associated with it A
112. ates a new version of the class NOTE A class connector connects to a specific GemStone class version the version that was in effect when the connector was connected Instances of a given class version are not affected by a connector connected to another class version 5 3 Forwarders The simplest way to share objects is with forwarders simple objects that know just one thing to whom to forward a message A forwarder is a proxy that responds to messages by forwarding them to its counterpart in the other object space Forwarders are particularly useful for large collections generally resident on the GemStone server whose size makes them expensive to replicate and cumbersome to handle in a client image Forwarders are of two kinds The most common kind of forwarder is a forwarder to the server a client Smalltalk object an instance of GbsFowarder that knows only which GemStone server object it represents It responds to all messages by passing them to the appropriate server object where its associated state resides and behavior is implemented For historical reasons this is the kind of forwarder usually meant when a discussion merely says forwarder This kind of forwarder is also called a server forwarder e A forwarder to the client is a GemStone server object that knows only which client Smalltalk object it represents It responds to all messages by passing 5 6 GemStone Systems Inc March 2006 Sharing Objects
113. ates to a minimum of n levels min 0 replicate max m faults in the instance variable and its referents as replicates to a maximum of m levels max 0 stub replicate faults in the instance variable as a replicate whose behavior will be subject to the configuration parameters fault levelRpc and faultLevelLnk relative to the root object being faulted By default an instance variable s behavior is replicate your application needn t specify replicates unless to restore behavior overridden in a superclass Example 5 6 TestObject class gt gt replicationSpec super replicationSpec instVarl stub instVar2 forwarder instVar3 max 0 instVar4 min 0 instVar5 max 2 instVar6 min 2 instVar7 replicate indexble_part min 1 Replication Specifications and Class Versions As explained in Mapping and Class Versions on page 5 6 client Smalltalk classes connect not simply to GemStone Smalltalk classes but to specific server class versions A class connector connects to only one server class version A replication spec therefore affects only client instances connected to instances of the correct GemStone class version Suppose for example that you define and redefine class X in the server until its class history lists three versions Your client Smalltalk class is connected to Version 2 Class X s replication spec will affect server instances of Class X Version 2 If the server contains inst
114. bed below Do not confuse these values with your GemStone username and password You do not need to supply a host user name and host password if you are starting a linked Gem process However an application that must control more than one GemStone session can use a linked interface for only one session Other sessions must use the RPC interface Gem service not required for a linked session The name of the Gem service on the host computer that is the Gem process to which your GemBuilder session will be connected For most installations the Gem service name is gemnetobject You can specify that the gem is to run on a remote node by using an NRS for the Gem service name For example pelican gemnetobject You do not need to supply a Gem Service name if you are starting a linked Gem process Once defined an instance of GbsSessionParameters can be used for more than one session Thus a session description that includes the RPC required parameters can be used for both linked and RPC logins Defining Session Parameters Programmatically The instance creation method for a full set of RPC parameters is GbsSessionParameters newWithGemStoneName aGemStoneName username aUsername password aPassword hostUsername aHostUsername hostPassword aHostPassword gemService aGemServiceName For a shorter set of parameters that supports only linked logins you can use a shorter creation method GbsSessionParameters newWithGemStoneName aG
115. ble any arbitrary group of classes and their instances to share information When classes share a pool dictionary 3 12 GemStone Systems Inc March 2006 Using the GemStone Programming Tools Coding methods defined in those classes can refer to the variables defined in the pool dictionary Step 9 After the inDictionary keyword the name of the selected symbol dictionary is inserted in the template This is the symbol dictionary that will allow you to refer to your class by name Unless you replace the inserted text with the name of another symbol dictionary to which you have access your new class is defined in the selected symbol dictionary Step 10 Fill in the brackets after the constraints keyword with any constraints you wish to specify for one or more of the instance variables To constrain the elements of a collection type the name of the constraint class inside the brackets For example to constrain the Bag subclass BagOfEmployees to contain only instances of the class Employee type constraints Employee To constrain a named instance variable type the name of the variable and the constraint class as a pair separated by a comma each within its own set of square brackets also separated by commas Preface the instance variable name with a For example to constrain the instance variables name and address of the class Employee to be a String and an instance of the class Address respectively type constra
116. bles declared external to the block s scope An exception is allowed in the case of global references such as class names e Global variable references from inside a block must have the same name in both object spaces In the case of global variables containing data it is the programmer s responsibility to ensure that the global identifier represents compatible values in both contexts Temporary variable reference restrictions disallow the following because tempName is declared outside the block s scope namedEmps tempName tempName Fred namedEmps myEmployees select anEmployee anEmployee name tempName As a workaround implement a new Employees method in GemStone Smalltalk named select with that evaluates a two argument block in which the extra block argument is passed in as the with parameter For example select aBlock with extraArg result result self speciesForSelect new self keysAndValuesDo aKey aValue aBlock value aValue value extraArg two value block ifTrue result at aKey put aValue A result March 2006 GemStone Systems Inc 5 33 Replicates GemBuilder User Manual You can then rewrite the application code to pass its temporary as the argument to the with parameter without violating the scope of the block namedEmps tempName tempName Fred namedEmps myEmployees select anEmployee extraArg anEmpl
117. bsSessionParameters new params gemStoneName gemserver61 params username DataCurator params password swordfish S s params gemService gemnetobject params rememberPassword true params rememberHostPassword true self addConnectorsTo params sessionParameters params GBSM addParameters params sessionParameters Example 6 4 adds connectors to the session parameters object by calling lower level methods to individual types of connectors Example 6 4 addConnectorsTo aParams self addClassConnectorsTo aParams self addClassVarConnectorsTo aParams Example 6 5 shows a method that creates class connectors and adds them to the session parameters connector list 6 14 GemStone Systems Inc March 2006 Connectors Making and Managing Connectors Example 6 5 addClassConnectorsTo aParams aParams addConnector GbsClassConnector stName GST_Action gsName GST_Action aParams addConnector GbsClassConnector stName GST_Customer gsName GST_Customer aParams addConnector GbsClassConnector stName GST_Engineer gsName GST_Engineer Example 6 6 shows a method that creates class variable connectors and adds them to the session parameters connector list Example 6 6 addClassVarConnectorsTo aParams aConnector aParams addConnector aConnector GbsClassVarConnector stName GST_HelpRequest gsName GST_HelpRequest cvarName All
118. bug it resolve self to the GemStone server object When the GS Delegate tab is selected Do it Print it Inspect it and Debug it resolve self to the delegate object as in Figure 4 4 4 4 GemStone Systems Inc March 2006 Debugging Breakpoints Figure 4 4 Evaluating self in the GS Delegate tab of the Inspector iojxi Object Edit Go History Explore Tools Help e gt 8 gaam Elements Basic Methods GS Elements GS Basic GS Delegate GS Methods gsOop session flags isSpecial self GbsObject oopValue 196853 4 3 Breakpoints For the purpose of determining exactly where a step will go during debugging a GemStone Smalltalk method is composed of step points You can set breakpoints at any step point Generally step points correspond to the message selector and within the method message sends assignments and returns of nonatomic objects However compiler optimizations may occasionally result in a different nonintuitive step point particularly in a loop Example 4 1 indicates step points with numbered carets March 2006 GemStone Systems Inc 4 5 Breakpoints GemBuilder User Manual Example 4 1 includesValue value AL Return true if the receiver contains an object of the same value as the argument Return false otherwise found index size found false 2 index 0 3 size self size 45 4 found not amp
119. can also change this value by using the Settings Browser choose GemStone gt Tools gt Settings and select the Server Communications category in the resulting Settings Browser 11 4 Optimizing Space Management In normal use of GemBuilder objects are faulted from GemStone to the client Smalltalk on demand In many ways however this is a one way street and the client Smalltalk object space can only grow Advantages can be gained if client Smalltalk replicates can be discarded when they are no longer needed A reduced number of objects on the client reduces the load on the virtual machine garbage collection and various other functions March 2006 GemStone Systems Inc 11 9 Optimizing Space Management GemBuilder User Manual Measures you can take to control the size of the client Smalltalk object cache include explicit stubbing using forwarders and not caching certain objects Explicit Stubbing If the application knows that a replicate is not going to be used for a period of time the space taken by that object can be reclaimed by sending it the message stubYourself More importantly any objects it references become candidates for garbage collection in your client Smalltalk Consider having replicated a set of employees After faulting in the set and the objects transitively referenced from that set the objects in the client Smalltalk look something like this Figure 11 1 Employee Set Faulted into the Client Smallta
120. can gemnetobject If convenience is more important than security you can fill in the passwords and then instruct the parameters object to retain the password information for future use mySessionParameters rememberPassword true rememberHostPassword true The default remember setting for both passwords is false which causes the stored passwords to be erased after login March 2006 GemStone Systems Inc 2 7 The GemStone Session Browser GemBuilder User Manual 2 4 The GemStone Session Browser The GemStone Session Browser streamlines logging in and logging out of GemStone and managing sessions and transactions This section explains how to invoke the Session Browser and how to use it to define session parameters and to log in and out of GemStone Starting the Session Browser 1 Start your GemBuilder for Smalltalk image 2 Select Browse Sessions from the GemStone menu to open a Session Browser Figure 2 2 shows the Session Browser Figure 2 2 The GemStone Session Browser lox DataCurator on gemserver61 Login Ln MEN Session 1 linked for DataCurator on gemserver61 E auto Commit Abort Begin Logout Current manual Supplying Session Parameters Select the Add button to define a set of session parameters A Session Parameters Editor appears as shown in Figure 2 3 2 8 GemStone Systems Inc March 2006 Communicating with the GemStone Object Serv
121. can resolve that reference only if it is in one of the dictionaries named in your symbol list The GemStone Smalltalk compiler searches for names in the following order 1 It first checks to see if the variable is local that is a temporary variable or argument 2 If the variable is not local the compiler checks to see if the variable is defined by the class that defines the current method or one of its superclasses 3 If it still cannot resolve the reference the compiler searches the symbol list in your UserProfile sequentially that is from top to bottom This means that if some name for example Supplier is defined in the first dictionary and in the last dictionary in your symbol list the compiler will find only the first definition Because you can use GemStone s symbol resolution mechanism to arrange to share or not to share any specific object with other GemStone users it is necessary for you to be aware of what is in your symbol list and to understand how to use symbol list dictionaries for sharing objects You can use GemBuilder s Symbol List Browser to do this See The Symbol List Browser on page 8 20 All you have to do to set up other users to share access to specified objects is to name the objects in question in a specific symbol dictionary then make sure that all the relevant users include that dictionary in the symbol list of their UserProfiles When you examine your symbol list dictionaries
122. ce of class Address The application has one screen that displays the names from a list of employees and another screen that displays the zip codes from a list of employee addresses Here s how to replicate only what s needed Step 1 Define a new replication spec with the selector empNamesRepSpec Step 2 Implement Object class gt gt empNamesRepSpec as self replicationSpec Step 3 Implement Employee class gt gt empNamesRepSpec as firstName min 1 lastName min 1 address stub Step 4 Define another replication spec with the selector empZipcodeRepSpec Step 5 Implement Object class gt gt empZipcodeRepSpec as self replicationSpec 5 24 GemStone Systems Inc March 2006 Sharing Objects Replicates Step 6 Define Employee class gt gt empZipcodeRepSpec as firstName stub lastName stub address min 2 and Address class gt gt empZipcodeRepSpec as city stub state stub zip min 1 Step 7 Before opening the employee names screen send myGbsSession replicationSpecSet empNamesRepSpec Restore it to replicationSpec after opening the window Step 8 Before opening the zip code window send myGbsSession replicationSpecSet empZipcodeRepSpec Restore it to replicationSpec after opening the window For each window the procedure above reduces the number of objects retrieved to the minimum required Other objects fault in as stubs if subsequent input
123. chanisms for safeguarding the objects in your GemStone repository These mechanisms are discussed in the chapter on creating and restoring backups in the GemStone System Administration Guide This chapter discusses security and access at the object level Not all these security features are available for all server product versions GemStone S 64 Bit 1 0 and 2 0 do not support Segments Much of the material in the chapter will not apply when using GBS with a GemStone S 64 Bit server Object Level Security highlights the mechanisms GemStone provides for keeping your stored objects secure Classes for Controlling Access to Objects describes the three key classes Repository Segment UserProfile that provide object level security Sharing Access to Objects explains how you can use GemStone s group authorization mechanism and March 2006 GemStone Systems Inc 8 1 Object Level Security GemBuilder User Manual the individual users UserProfiles to ensure that users have appropriate access to the objects they need GemStone Administration Tools describes the visual tools that you can use to manage access to objects by multiple users the Segment Tool the Symbol List Browser and the User Account Management Tools 8 1 Object Level Security GemStone provides for blocking access to certain objects as well as sharing them Applications can take advantage of several security mechanisms to prevent unauthorized access to o
124. cial Software Restricted Rights clause at 52 227 19 of the Federal Acquisitions Regulations 48 CFR 52 227 19 except that the government agency shall not have the right to disclose this software to support service contractors or their subcontractors without the prior written consent of GemStone Systems Inc This software is provided by GemStone Systems Inc and contributors as is and any expressed or implied warranties including but not limited to the implied warranties of merchantability and fitness for a particular purpose are disclaimed In no event shall GemStone Systems Inc or any contributors be liable for any direct indirect incidental special exemplary or consequential damages including but not limited to procurement of substitute goods or services loss of use data or profits or business interruption however caused and on any theory of liability whether in contract strict liability or tort including negligence or otherwise arising in any way out of the use of this software even if advised of the possibility of such damage COPYRIGHTS This software product its documentation and its user interface 1986 2006 GemStone Systems Inc All rights reserved by GemStone Systems Inc PATENTS GemStone is covered by U S Patent Number 6 256 637 Transactional virtual machine architecture Patent Number 6 360 219 Object queues with concurrent updating and Patent Number 6 567 905 Generational Garbage Co
125. could implement an initialize method in your application model as shown in Example 11 1 Example 11 1 self session sendNotificationEventsTo self sendSignaledAbortEventsTo self The second step is to reimplement windowEvent rom in your ApplicationModel subclass to respond to the appropriate corresponding events gemSignalAction notificationAction or SignaledAbortAction as shown in Example 11 2 Example 11 2 windowEvent anEvent from aWindow super windowEvent anEvent from aWindow anEvent key SignaledAbortAction ifTrue Transcript cr show Aborting and refreshing the view self session abortTransaction self updateView anEvent key notificationAction ifTrue March 2006 GemStone Systems Inc 11 15 Multiprocess Applications GemBuilder User Manual anl Event value includes someList ifTrue Transcript cr show List modified by another session Gr show aborting and refreshing view self session abortTransaction self updateView 11 16 GemStone Systems Inc March 2006 Appendix Configuring GemBuilder This appendix describes the Settings Browser and GemBuilder configuration parameters their default and legal values and their significance GemBuilder Configuration Parameters GemBuilder provides configuration settings that allow GemBuilder to operate diffe
126. ct Access Sharing Access to Objects Group Authorization and Object sharing When you have a group of users working with the same GemStone application you need to arrange for everyone in the group to have access to the objects that need to be shared such as the application classes You might also want to limit access to certain data objects to some specified users While an application s developer may require full read and write access to all its objects the end users may need to see them all but only modify a few GemStone users generally fall into three categories e developers who define classes and methods e updaters who create and modify instances and e reporters who read and output information GemStone s segment mechanism allows you to provide the appropriate level of access for each type of user by organizing users who have common interests or needs into designated groups Like segment owners groups can be given the authorizations write read or none When a GemStone user tries to read or write an object assigned to a particular segment GemStone compares the group authorizations stored by the segment with the group memberships stored in that user s UserProfile If there is a group in common and if the authorization for that group permits what the user is trying to do the operation is allowed to continue if not barring other relevant authorizations the operation is halted If your default segment is associ
127. ction mode a transaction begins only as a result of an explicit request When you abort or commit successfully the session remains outside a transaction until a new transaction is initiated To begin a transaction send the message aGbsSession beginTransaction or select the Begin button on the Session Browser A new transaction always begins with an abort to refresh the session s private view of the repository Local objects that customarily survive an abort operation such as temporary results you have computed while outside a transaction can be carried into the new transaction where they can be committed subject to the usual constraints of conflict checking If you begin a new transaction while already inside a transaction the effect is the same as an abort In manual transaction mode as in automatic mode an unsuccessful commit leaves the session in the current transaction until you take steps to end the transaction by aborting Choosing Which Mode to Use You should use automatic transaction mode if the work you are doing requires committing to the repository frequently because you can make permanent changes to the repository only when you are in a transaction Use manual transaction mode if the work you are doing requires looking at objects in the repository but only seldom requires committing changes to the repository You will have to start a transaction manually before you can commit your changes to the repository but the
128. cumented in this User s Guide This User s Guide documents the preferred way to accomplish tasks Other public classes or methods may be obsolete but kept for backward compatibility Deprecated Features GemBuilder may include features that are deprecated in the current release This indicates that although the feature is still functional it may be removed in a future release In your applications you should eliminate any dependencies on deprecated GemBuilder features You can find all deprecated features of GemBuilder by browsing the senders of deprecated To help you determine whether your application uses any deprecated features GemBuilder by default raises a GemStone Gbs GbsInterfaceError whenever a deprecated feature is used The description of the GbsInterfaceError gives information about the deprecated feature that was being used 1 10 GemStone Systems Inc March 2006 Basic Concepts Delivery and Deployment If your application does not have an active handler for GbsInterfaceError when a deprecated feature is used a walkback dialog will open Once you ve noted information about your application s use of the deprecated feature you may proceed from the walkback or debugger and your application will continue This is a useful technique for a developer testing for use of deprecated features Once you ve noted a particular use of a deprecated feature you can avoid further walkbacks from that use until you ar
129. d Managing Connectors Session Control The following examples illustrate one approach to managing GemBuilder sessions and connectors a session control class that defines these methods for in this example a help request system An instance of the session control class could be stored in the application object as a class variable in which case the session information would be the same for all instances of the application or it could be stored in the application as an instance variable in which case each instance of the application would get its own copy to change as needed In either case methods to create the session parameters object and its connectors might follow these patterns Example 6 2 shows the method session which returns the application s logged in session If the session is not logged in the method requests an RPC login and returns the resulting session If login fails the method returns nil Example 6 2 session self session session isNil or session isLoggedIn not ifTrue session self sessionParameters loginRpc session isNil ifTrue nil session Example 6 3 shows a method that initializes a set of session parameters For security you may choose to prompt for passwords instead March 2006 GemStone Systems Inc 6 13 Making and Managing Connectors GemBuilder User Manual Example 6 3 sessionParameters params sessionParameters isNil ifTrue params G
130. d and written back to the server the server instance will be of the newer class version This will lazily migrate forward server instances to newer class versions For example suppose you have a class named Foo on the GemStone server and there are two versions of it Foo 1 and Foo 2 Suppose that client Smalltalk has a representation of Foo 2 Instances of Foo 2 are replicated back and forth between client and server as usual If GemBuilder attempts to fault an instance of Foo 1 however GemBuilder will discover that there is no class mapping for Foo 1 GemBuilder will then do the following 1 It will fetch the name of the GemStone server class and discover that there is a client Smalltalk class by the same name that is already mapped to a server class 2 It will verify that the two server classes are in the same class history and that the version of Foo 1 is less than the version of Foo 2 3 It will then ask GemStone to make a copy of the Foo 1 instance migrate the copy to Foo 2 and replicate that migrated copy to the client The client replicate is mapped to the original Foo 1 server instance 4 Tf the client replicate is later modified in client Smalltalk marked dirty and flushed to the server it will not be migrated back and the server object will become an instance of Foo 2 This process is fairly expensive If you are running GemBuilder in verbose mode the discovery of an client Smalltalk class th
131. d for the world Note that segments do not know which objects are assigned to them nor are they meant to organize objects for easy listing and retrieval that is the role of symbol lists UserProfile When you become a GemStone user you are assigned a UserProfile object Your UserProfile stores information about you as an individual user such as your name your password and a list of symbol dictionaries that the compiler can consult to find the objects named in your applications Your UserProfile also stores a reference to a segment that serves as your default segment When you create objects GemStone assigns them to your default segment unless you specify otherwise You can be the owner of your default segment or the system administrator may have assigned ownership to someone else March 2006 GemStone Systems Inc 8 5 Sharing Access to Objects GemBuilder User Manual You can use your default segment for all the objects you create but if you have the proper privileges you can exert more control over access to your objects by creating additional segments For example you can create the classes and other objects for an application in a private segment and then reassign them to segments that other users can access Your current segment is the same as your default segment when you log in but you can designate a different segment to be your current segment so that subsequent new objects will be assigned to it instead of to your d
132. d in the class list The browser displays the class definition template NameOfSuperclass subclass NameOfClass instVarNames instVarNamel instVarName2 classVars ClassVarNamel1 ClassVarName2 classInstVars ClassInstVarNamel1 ClassInstVarName2 poolDictionaries inDictionary aDictionary constraints instancesInvariant false isModifiable false This is the basic form of the subclass creation message in GemStone Smalltalk Step 3 Replace NameOfSuperclass with the name of your new class s immediate superclass Step 4 Replace NameOfClass with the name of the new class By convention the first letter of each GemStone class name is capitalized Step 5 Replace instVarName with the names of any instance variables or delete all the text within the parentheses if your new class has no instance variables A class can define up to 255 named instance variables Step 6 Replace classVarNames with the names of any class variables or delete all the text within the parentheses if your new class has no class variables Step 7 Replace classInstVarNames with the names of any class instance variables or delete all the text within the parentheses if your new class has no class instance variables Step 8 Fill in the brackets after the poolDictionaries keyword with any pool dictionaries that you want the class to access Pool dictionaries are special purpose storage structures that ena
133. d lastName March 2006 GemStone Systems Inc 5 25 Replicates GemBuilder User Manual You could ensure this by implementing Employee class gt gt replicationSpec to include firstName min 1 and lastName min 1 Or if you had a special Dictionary class for Employees you could include indexable_part min 3 in that dictionary class s replication spec However this could cause the entire Employee to be replicated whenever one of these dictionaries is replicated rather than just the firstName and lastName We recommend that you use the default replication spec replicationSpec as the base replication spec for all classes to reflect interobject dependencies When defining other replication specs make sure the default implementation in Object is self replicationSpec Ensure that subclass implementations of the new replicationSpec method do not stray from the default so as not to break interobject dependencies Precedence of Multiple Replication Specs It s possible to implement replication specs that appear to contradict each other Such apparent conflicts are resolved deterministically according to the order in which instance variables appear in a replication spec and the order in which objects are replicated If a superclass specifies one way of handling an instance variable and a subclass reimplements replicationSpec to handle the same variable in a different way the last occurrence takes precedence
134. date the client or create a forwarder 6 3 Kinds of Connectors Five kinds of connectors use different ways of finding the two objects to connect You have already encountered one kind Class connector connects a client Smalltalk and GemStone class As discussed in Class Mapping on page 5 3 to replicate an object both client and repository must define the class and the two classes must be connected using a class connector For replicating instances however we need ways to connect root objects Name connector connects client and server objects identified by name Figure 6 3 illustrates how a name connector connects a client object to a server object Class variable connector first resolves the named objects representing the classes then looks for a class variable in the GemStone class and a Class or Shared Variable in the client Smalltalk class with the specified name and connects those objects Class instance variable connector first resolves the named objects representing the classes then looks for a class instance variable in each class with the specified name and connects those objects Fast connector connects the GemStone kernel classes to their client Smalltalk counterparts Fast connectors are predefined implemented for speed The kernel classes to which they point will not change identity during the course of a session GemBuilder can take advantage of that to reduce overhead The GemStone kern
135. de in the client Smalltalk Objects are stored in GemStone for persistence and sharing but are replicated in the client Smalltalk for manipulation In general this policy works well There are times however when it is preferable or required to execute in GemStone One motivation for preferring execution in GemStone is to improve performance Certain functions can be performed much more efficiently in GemStone The following section discusses the trade offs between client Smalltalk and server Smalltalk execution and how to choose one space over the other Beyond optimization some functions can be performed only in GemStone GemStone s System class for example cannot be replicated in the client Smalltalk messages to System have to be sent in GemStone Locus of Execution This section centers on controlling the locus of execution in other words determining whether certain parts of an application should execute in the client Smalltalk or in GemStone Subsequent sections discuss other ways of tuning to increase execution speed 11 6 GemStone Systems Inc March 2006 Performance Tuning Selecting the Locus of Control Client Smalltalk and GemStone Smalltalk are very similar languages Using GemBuilder it is easy to define behavior in either client Smalltalk or GemStone to accomplish the same task There are however performance implications in the placement of the execution This section discusses several factors to weigh w
136. der aForwarder select e e isNil asBlockCallback You can determine whether by default blocks are replicated or call back to the client using GemBuilder s configuration parameter blockReplicationPolicy Legal values replicate and callback A value of replicate causes a client block to be stored in GemStone as a GemStone block A value of callback causes a client block to be stored in GemStone as a client forwarder so that sending value to the block in GemStone causes value to be forwarded to the client block the result of that block evaluation is then passed back to the GemStone context that invoked the block To ensure a specific replication policy for a given block use the methods asBlockCallbackor asBlockReplicate Send asBlockCallback to ensure that the block always executes in the client regardless of the default block March 2006 GemStone Systems Inc 5 35 Precedence of Replication Mechanisms GemBuilder User Manual replication policy set by the configuration parameter Likewise send asBlockReplicate to ensure that the block is executed local to the context that invokes it either in GemStone or in the client For example dictionaryForwarder at X ifAbsent nil asBlockCallback collectionForwarder do e e check asBlockReplicate Replicating Collections with Instance Variables If you create a subclass of a Collection and give it instance variables you must re
137. descriptions in both the client and GemStone server Smalltalks In the Connector pane the popup menu offers the following items Table 6 2 Connectors Menu in the Connector Browser inspect Client Resolves and inspects the client Smalltalk object for the selected connector inspect Server Resolves and inspects the GemStone server object for the selected connector add Adds a new connector prompting for required information remove Removes a connector after confirmation The Control Panel The bottom pane is a control panel that allows you to change the connectVerification and removelnvalidConnectors configuration parameters March 2006 GemStone Systems Inc 6 17 Making and Managing Connectors GemBuilder User Manual and connect or disconnect objects setting a connector s postconnect action is described in the section that follows Table 6 3 Options in the Control Panel Global verification When enabled connectors other than class connectors verify that they are not redefining an object connection before connecting Class connectors upon connection verify that the structures of the two connected classes are of the same storage type Remove bad connectors When enabled connectors that fail to resolve at login are automatically removed from the connector collections Connected Disconnected Connects or disconnects the GemStone and client Smalltalk objects described by the connector Applies to the sel
138. e subsystems in GemStone S this way After you ve connected the application s roots GemBuilder automatically manages all the objects referenced from these roots Root objects are often e global variables e class or shared variables or e class instance variables Figure 6 1 shows an application in which several connected objects are accessed through global or shared variables in client Smalltalk One system represents an employee database Another system represents a data entry application for creating and modifying objects A third system represents a report writer for these objects Dotted lines in the figure group the logically related subsystems 6 2 GemStone Systems Inc March 2006 Connectors Connecting Root Objects Figure 6 1 Connecting Application Roots l l a y Sle a es Data Entry Application Yo gt 7 Report Writer The data entry application and the report writer reside in the client Smalltalk image however the employee database is stored on the GemStone server as it defines a large amount of persistent data that other users may need to share data that benefits from GemStone S s capacity stability robustness and fast searches Figure 6 2 shows the state of the employee data when stored on the server March 2006 GemStone Systems Inc 6 3 Connecting Root Objects GemBuilder User Manual Figure 6 2 Root Objects
139. e Stone and one or more user processes called Gems Figure 1 1 shows how the object server supports clients in a Smalltalk application environment Figure 1 1 The GemStone Object Server Application A Application B Client Smalltalk Client Smalltalk classes and objects classes and objects Gem Process A Gem Process B GemStone GemStone classes and objects classes and objects Stone monitor process Object Repository GemStone Object Server Relational Data The object repository is a multiuser disk based Smalltalk image containing shared application objects and GemStone kernel classes It is composed of files 1 2 GemStone Systems Inc March 2006 Basic Concepts GemBuilder for Smalltalk known to GemStone as extents that can reside on a single machine or can be distributed among several networked hosts The repository can also include GemConnect objects representing data stored in third party relational databases Your Smalltalk application program treats the repository as a single unit regardless of where its elements physically reside A Gem is an executable process that your application creates when it begins a GemStone session A Gem acts as an object server for one session providing a single user view of the multiuser GemStone repository A Gem reads objects from the repository executes GemStone Smalltalk methods and updates the
140. e able to remove that use from your application You can do this by adding a handler for the GbsInterfaceError that resumes the exception at the point in your application that the deprecated feature is used You may also set the GemBuilder configuration parameter deprecationWarnings to false as described in Appendix A When deprecationWarnings is false any code in the client image may use any deprecated GemBuilder feature without raising a GosInterfaceError March 2006 GemStone Systems Inc 1 11 Delivery and Deployment GemBuilder User Manual 1 12 GemStone Systems Inc March 2006 Chapter Communicating with the GemStone Object Server When you install GemBuilder your Smalltalk image becomes GemStone enabled meaning that your image is equipped with additional classes and methods that allow it to work with shared persistent objects through a multi user GemStone object server Your Smalltalk image remains a single user application however until you connect to the object server To do so your application must log in to a GemStone object server in much the same way that you log in to a user account in order to work on a networked computer system This chapter explains how to communicate with the GemStone object server by initiating and managing GemStone sessions Client Libraries explains how to setup to use the correct client shared libraries GemStone Sessions introduces sessions and expl
141. e chapters that discuss these topics in detail Which objects should be stored and shared Your application will typically have two kinds of objects those that must persist between sessions and be shared among users and those that represent a transient state Your first task is to identify the objects that make up your application and decide which ones need to be stored and shared Making objects persistent unnecessarily can degrade performance and complicate programming Use the GemStone server to store those objects that need to exist between sessions and must be shared with other users For example objects representing information in your application such as financial statements employee health records or library book cards would certainly require storage in the server Some methods for manipulating the persistent data can also be usefully coded in GemStone Smalltalk and stored in GemStone for improved efficiency You don t need to store transient session objects that no one else will ever need on the server such objects can remain in the client For example suppose you generate a report from the financial statements stored in GemStone Once you view or print the report it has served its purpose the next time you need a report you will generate a new one The report and its component objects can exist simply as client Smalltalk objects they don t need to be stored in GemStone March 2006 GemStone Systems Inc 1 7 Desi
142. e method returns a value Because no GemStone Smalltalk code has yet been encountered the virtual machine has not yet reached the first step point Only if the primitive fails will the virtual machine execute the message send at the bottom of the method and thus encounter the breakpoint Breakpoints for Optimized Methods Certain simple methods are optimized by the GemStone Smalltalk compiler in such a way that they contain no step points Naturally you cannot set a method breakpoint if there are no step points A method that performs only one of the following operations has no step points e return true e return false e return nil e return self e return the value of an instance variable e assign to an instance variable or e return a class or pool variable or a variable defined in a symbol dictionary A method that performs some computation and then performs one of the actions listed above contains step points it is not a simple method for purposes of this discussion March 2006 GemStone Systems Inc 4 7 Breakpoints GemBuilder User Manual In addition to the special methods listed above a handful of specific kernel class methods are specially optimized so that they cannot take breakpoints Those methods are ifTrue whileTrue timesRepeat ifFalse isKindof to do ifTrue ifFalse _isInteger to by do ifFalse ifTrue _isSmalliInteger untilFalse _isSymbol untilTrue _or _class whileFalse
143. e session your application should send messages directly to each session If your application client uses multiple Smalltalk processes it is very difficult to accurately coordinate the changing of the current session Sending the message GBSM currentSession returns the current GbsSession You can change the current session in a workspace by executing an expression of the following form GBSM currentSession aGbsSession Your application can make another session the current session by executing code like that shown in Example 2 1 Example 2 1 s1 s2 sl GBSM login s2 GBSM login GBSM currentSession sl Make sl current Do some work GBSM currentSession s2 Make s2 current March 2006 GemStone Systems Inc 2 11 Logging In To and Logging Out Of GemStone GemBuilder User Manual Each GemStone browser inspector debugger and breakpoint browser is attached to the instance of GbsSession that was the current session when it opened For example you can have two browsers open in two different sessions such that operations performed in each browser are applied only to the session to which that browser is attached Workspaces however are not session specific GS Do its executed in a workspace default to the current session Logging Out of GemStone Programmatically To instruct a session to log itself out send logout to the session object aGbsSession logout Or you can execute
144. e with the operate mouse button The GemStone specific commands in the popup menus of the Symbol List Class Categories and Methods panes are described below March 2006 GemStone Systems Inc 3 5 Browsing Code GemBuilder User Manual Symbol List Pane The GemStone specific menu options available in the Symbol List pane shown in Table 3 2 Table 3 2 Symbol List Menu in GemStone Browser file out as file out methods as spawn inspect add rename as remove update commit abort find class Prompts you for a file name under which to save all the class and method definitions for all the classes in the selected SymbolDictionary Prompts you for a file name under which to save all the methods in all the classes in the selected SymbolDictionary so that you can file them into a client class without creating a new version of the class Open a Dictionary Browser on the selected SymbolDictionary Open an inspector on the selected SymbolDictionary Add a new Symbol Dictionary Rename the selected SymbolDictionary Remove the selected SymbolDictionary Do not remove Globals Update the view of the browser to the current state in the image Attempts to commit modifications to the repository that occurred during the current GemStone transaction Undoes all changes that you have made in the repository since the beginning of the current transaction You are asked to confirm this ch
145. e your own default segment select the desired segment by clicking in its row Then choose Segment gt Make Default To change someone else s default segment in the GemStone User Dialog choose Show Segments 1 In the Segment Tool select the desired segment by clicking in its row Choose Segment gt Grab In the GemStone User Dialog choose Paste To Default Segment Choose OK or Apply NOTE Changes to a segment s authorization do not take effect until the current transaction is committed This means that if you change any user s default segment including your own to a segment for which that user lacks write authorization and you subsequently commit the transaction the affected user will no longer be able to log in to GemStone March 2006 GemStone Systems Inc 8 19 GemStone Administration Tools GemBuilder User Manual The Symbol List Browser The Symbol List Browser is a tool for examining the GemStone SymbolLists associated with UserProfiles adding and deleting dictionaries from these lists examining the entries in those dictionaries and adding deleting and inspecting the entries References to dictionaries and dictionary entries can be copied between GemStone user accounts subject to authorization and segment restrictions to allow users to share application objects and name spaces developed by other users and to publish them to other users To open a Symbol List Browser select Admin gt Symbol Lists
146. eDictionary This class provides the same functionality as KeyValueDictionary except that no conflict occurs on instances of RcKeyValueDictionary when users read 7 16 GemStone Systems Inc March 2006 Managing Transactions Changed Object Notification values in the dictionary or add keys and values to it unless one tries to add a key that already exists or when users remove keys from the dictionary at the same time unless more than one user tries to remove the same key at the same time Conflict occurs only when more than one user tries to modify or remove the same key from the dictionary at the same time RcQueue The class RcQueue represents a first in first out FIFO queue No conflict occurs on instances of RcCQueue when multiple users read objects in or add objects to the queue at the same time or when one user removes an object from the queue while other users are adding objects However if more than one user removes objects from the queue they are likely to experience a write write conflict 7 7 Changed Object Notification A notifier is an optional signal that is activated when an objects committed state changes Notifiers allow sessions to monitor the status of designated shared application objects A program that monitors stock prices for example could use notifiers to detect changes in the prices of certain stocks In order to be notified that an object has changed a session must register that object with the
147. ecent version of the repository and you can continue your work Close Close the Segment tool Any changes made are kept but not commited to the repository 8 14 GemStone Systems Inc March 2006 Security and Object Access GemStone Administration Tools Table 8 2 Segment Menu Use the Segment menu to create new segments and to manipulate existing segments Segment Menu in the Segment Tool Create Creates anew segment You must have the SegmentCreation privilege to use this option In the Create Segment dialog enter a name for the segment and a symbol dictionary to store itin Private segments are typically kept in UserGlobals Segments for large groups of users are typically kept in Globals Grab Grabs a reference to the selected segment and places it on the clipboard This can be used to add a reference to a user s symbol list or for changing the default segment of a user in the User Dialog Make Current Makes the selected segment your current segment When you create an object GemStone assigns it to your current segment Make Default Makes the selected segment your default segment This is the home segment that is your current segment when you log into GemStone March 2006 GemStone Systems Inc 8 15 GemStone Administration Tools GemBuilder User Manual Group Menu Use the Group menu to add and remove groups Table 8 3 Group Menu i
148. ected class version browse hierarchy Opens a Class hierarchy Browser that includes superclasses and subclasses of the selected class version browse versions Opens another Class Version Browser on this class history browse references This menu item has two submenus to this version of this class and to any version of this class Opens a method list browser containing all methods whose compiled code contains a reference to this version of the class or to any version of the class in this class history hierarchy Lists the superclasses and subclasses of the current class Any instance variable names declared in a class appear in the hierarchy list in parentheses definition Displays the definition that is the subclass creation message of the currently selected GemStone class version This is shown by default 10 8 GemStone Systems Inc March 2006 Schema Modification and Coordination The Class Version Browser Table 10 1 Class Menu in Class Version Browser Continued comment Displays the class comment if one exists move to Moves the selected class version to another class history Prompt for a target class adds the selected version to the target class s class history and updates the browser The class name of the selected version is changed to that of the target class remove Remove the selected class version from the class history Upon
149. ected session or to the current session if global connectors are selected Enabling connector verification can slow login we recommend that you turn on verification during development and turn it off for production systems Postconnect Action The postconnect action determines how GemBuilder sets the initial state of connected objects Options are Table 6 4 Postconnect Action Options in the Connector Browser updateST Initializes the client object using the current state of the GemStone server object 6 18 GemStone Systems Inc March 2006 Connectors Making and Managing Connectors Table 6 4 Postconnect Action Options in the Connector Browser Continued updateGS Initializes the GemStone server object using the current state of the client object forwarder Makes the client object a forwarder to the GemStone server object clientForwarder Makes the GemStone server object a forwarder to the client object none Leaves the client object and the GemStone server object unchanged after their initial connection The connector in the case has no function so it s unlikely you ll want to use this option To create a new connector 1 2 3 4 5 6 7 Select the session in the Group pane Place the cursor in the Connector pane Select add from the menu When prompted specify the type of connector When prompted specify the names of the client and server objects When prompted specify the name of the dicti
150. ects you will want to set up connections between the objects that will reside on the client and those that will reside on the server so that GemBuilder can automatically manage changes to them and understand how to update them properly This connection is established by making sure a connector is defined for those objects A connector connects not only the immediate object but also all those objects that it references so you don t need to define a connector for every object in your application that you want to store in the GemStone server Instead you should begin by identifying the subsystems in your application that define persistent objects and then identifying a root object in each subsystem to target with a connector You can find further discussion of connectors in Chapter 6 1 8 GemStone Systems Inc March 2006 Basic Concepts Delivery and Deployment How should transactions be handled Another decision you need to make involves transactions when to commit and how to handle the occasional failure to commit Do you want to use locks to ensure a successful commit If so identify the places in your application where you must acquire the locks Concurrency control and locking are discussed in more detail in Chapter 7 How can performance be improved If after you have built your application you find that its performance does not meet your expectations you have a variety of ways to improve matters One of the most p
151. edefinition have the new class s structure and access the new class s methods Instances that were created earlier have the old class s structure and access the old class s methods but they can be migrated to the new class Let s assume that you have a class named Employee with instance variables for name employeeNum jobTitle department and address and that the class is defined as shown in Figure 3 1 Two of Employee s instance variables are constrained to be instances of class String and one employeeNum is constrained to be a SmallInteger Suppose that you decide that the class needs an additional instance variable named salary to represent the Employee s salary To do this you can define a new version of the class Employee to include the new instance variable Keeping the same name as the old class ensures that it shares the same class history as the previous version After you compile the class definition the new class is named Employee and all of the original instance and class methods are copied to the new class Any existing instances will still belong to the original class and may have to be migrated to the new class See Instance Migration Within GemStone on page 10 2 3 16 GemStone Systems Inc March 2006 Using the GemStone Programming Tools Coding Defining Methods You can modify only methods for which you have write authorization for example methods that you have written for your ow
152. efault segment As a segment s owner you have control over the access that you and others have to the objects assigned to it and you can authorize access separately for e owner You can also alter your own access rights at any time even forbidding yourself to read or write objects assigned to the segment e groups You can authorize groups of users by name e world You can provide or restrict access to all GemStone users Note that these categories can overlap If you lose write authorization to your current segment your default segment becomes your current segment as soon as the transaction that changed authorization is committed If you lose write authorization to your default segment GemStone terminates your session with an error because GemStone execution cannot continue without permission to create temporary objects in some segment You can find out information about your default segment by executing System myUserProfile defaultSegment with a GS Print it The system will return something like this Segment Number 1 in Repository SystemRepository Owner SystemUser write World read 8 3 Sharing Access to Objects Two conditions must be present for a group of users to share access to an object e The object must be assigned to a segment that authorizes all the users to access it e The object must also be accessible from each user s Symbol List 8 6 GemStone Systems Inc March 2006 Security and Obje
153. efined by class WriteStream The Source Pane If you have selected a breakpoint in the break pane the text area displays the source code for that method This pane is similar to the GemStone Browser text area but you cannot recompile an edited method by executing Save 4 4 Debugger The GemStone Debugger is integrated with the client Smalltalk debugger allowing you to e view GemStone Smalltalk and client Smalltalk contexts together in one stack March 2006 GemStone Systems Inc 4 9 Debugger GemBuilder User Manual set and clear breakpoints without modifying source code e select a context from among those active on the virtual machine stack e examine and modify objects and code within that context and e continue execution either normally or in single steps Depending on the client Smalltalk version when GemStone Smalltalk execution is interrupted because of aruntime error a breakpoint an interrupt from the user or an Object pause it either directly opens the Debugger or a notifier that includes a Debug button Selecting the Debug button opens the Debugger The Debugger s stack pane displays the active call stack and allows you to choose some context stack frame from that stack for manipulation in the window s other panes The top contexts are GemStone Smalltalk contexts If you can scroll downward through the messages on the stack you will come to GS Executed Code this is where the GemStone and client Sm
154. el class connectors are predefined and GemBuilder relies on them You cannot convert them to forwarders NOTE Application objects can change identity during the course of a session Applications should therefore not define fast connectors March 2006 GemStone Systems Inc 6 7 Kinds of Connectors GemBuilder User Manual Connection Order At login GemBuilder connects connectors in the following order 1 First predefined fast connectors for kernel classes 2 next class connectors whose postconnect action is anything other than updateGS and finally 3 all other connectors in no particular order You can control the order in which connectors connect by connecting them explicitly in your code instead of relying on GemBuilder s automatic mechanism to connect them for you at login Lookup Names must be found in namespaces In the client objects included in a Smalltalk namespace can be visible throughout the Smalltalk image GemStone implements namespaces with symbol dictionaries if the symbol list of the session user includes the symbol dictionary defining object A then object A is visible to that user Lookup occurs when the connection is established that is when the session first logs in 6 8 GemStone Systems Inc March 2006 Connectors Kinds of Connectors Figure 6 3 Connecting a Name Connector Client Smalltalk GemStone Smalltalk Namespace GemStone user s symbol list
155. emStone and the users in each group Segment Report Produces a list of segments the user has read authorization for and displays information about each one as to e its owner e the groups for which it contains access information and e the access it grants to the owner groups and world This report includes the GsIndexing segment for which all users have read and write authorization User Report Produces a list of all GemStone users and shows each user s group memberships Segments that appear as Unnamed are not in your symbol list Thus their names and dictionaries are unknown Help Menu The Help menu contains one item Session Info which provides information about the session for the Segment Tool window and about the current session Using the Segment Tool If you are a segment s owner you can determine who has access to objects assigned to that segment For more information see the chapter on administering user accounts and segments in the GemStone System Administration Guide March 2006 GemStone Systems Inc 8 17 GemStone Administration Tools GemBuilder User Manual Checking Segment Authorization Anyone who has read authorization for a segment can use the Segment Tool to find out who is authorized to read or write that segment by doing the following 1 Bring up the Segment Tool by selecting GemStone gt Admin gt Segments or by choosing Show Segments in a GemStone User Dial
156. emStoneName username aUsername password aPassword GemStone Systems Inc March 2006 Communicating with the GemStone Object Server Session Control in GemBuilder Storing Session Parameters for Later Use If you want the GemBuilder session manager to retain a copy of your newly created session description for future use you must register it with GBSM GBSM addParameters aGbsSessionParameters Once registered with GBSM and saved with the image the parameters are available for use in future invocations of the image In addition the Session Browser and other login prompters make use of GBSM s list of session parameters Executing the expression GBSM knownParameters returns an array of all GbsSessionParameters instances registered with GBSM To delete a registered session parameters object send removeParameters to GBSM GBSM removeParameters aGbsSessionParameters Password Security You can control the degree of security that GemBuilder applies to the passwords in a session parameters object For example when you create the parameters object you can specify the passwords as empty strings When the parameters object is subsequently used in a login message GemBuilder will prompt the user for the passwords For example mySessionParameters GbsSessionParameters newWithGemStoneName pelican gemserver61 username DataCurator password a hostUsername lisam hostPassword e gemService peli
157. en migrate the instances of the old class to a completely different class by specifying a different migration destination as part of the message that performs the migration You can erase the migration destination for a class by sending it the message cancelMigration and you can query the migration destination by sending migrationDestination to the class Migrating Objects A number of mechanisms are available to allow you to migrate one instance or a specified set of instances to a previously specified migration destination or to another explicitly specified destination You can execute the following expression to identify instances that may need to be migrated SystemRepository listInstances anArrayOfClasses The listInstances message takes as its argument an array of classes and returns an array of sets The contents of each set consists of all instances whose class is equal to the corresponding element in the argument anArrayOfClasses Instances to which you lack read authorization are omitted without notification The simplest way to migrate an instance of an older class is to send the message migrate to the instance If the object is an instance of a class for which a migration destination has already been defined the object becomes an instance of the specified version of the class If no destination has been defined no change occurs March 2006 GemStone Systems Inc 10 3 Schema Modification GemBuilder U
158. ency conflicts that can cause a commit to fail Optimistic concurrency control risks higher rates of commit failure in GemStone Systems Inc March 2006 Managing Transactions Operating Inside a Transaction exchange for reduced transaction overhead while pessimistic concurrency control uses locks of various kinds to improve a transaction s chances of successfully committing GemBuilder also offers reduced conflict classes that are similar to familiar Smalltalk collections but are especially designed for the demands of multiuser applications This chapter explains each of the topics mentioned here transactions committing and aborting running outside a transaction automatic and manual transaction modes optimistic and pessimistic concurrency control and reduced conflict classes Be sure to refer to the related topics in the GemStone Programming Guide for a full understanding of these transaction management concepts 7 2 Operating Inside a Transaction While a session is logged in to the GemStone object server GemBuilder maintains a private view of the shared object repository for that session To prevent conflicts that can arise from operations occurring simultaneously in different sessions in the multiuser environment GemBuilder encapsulates each session s operations in a transaction Only when the session commits its transaction does GemStone try to merge the modified objects in that session s view with the main shared re
159. ent occurs the block you supply to these methods runs in a separate process Unless your main execution process is idle when these events occur you need to take the same precautions as any other application running multiple processes against a single session Applications that have multiple processes running against a single GemStone session should take these additional precautions e coordinate transaction boundaries e coordinate flushing e coordinate faulting GemBuilder provides a method GbsSession gt gt critical aBlock that evaluates the supplied block under the protection of a semaphore that is unique to that session The best approach to creating an application that must support more than one process interacting with a single GemStone session is to organize March 2006 GemStone Systems Inc 11 13 Multiprocess Applications GemBuilder User Manual its logical transactions into short operations that can be performed entirely within the protection of GbsSession gt gt critical All of that session s commits aborts executes forwarder sends flushes and faults should be performed within GbsSession gt gt critical blocks For example a block that implements a writing transaction will typically start with an abort make object modifications and then finish with a commit A block that implements a reading transaction might start with an abort perhaps perform a GemStone query and then maybe display the result in the
160. er The GemStone Session Browser Figure 2 3 The Session Parameters Editor Y Session Parameters Editor x GemStone repository pelican gemserver61 GemStone username DataCurator xnxx GemStone password Remember Host username lisam ARA Host password Remember Gem Service pelican gemnetobject Cancel Use the Tab key or the mouse to move through the fields in the login dialog and the Return key to accept input or changes in the login dialog Provide the session parameters described previously see Defining Session Parameters on page 2 5 For maximum password security leave the Password and Host Password fields empty and the Remember boxes unselected When you click on OK GemBuilder creates an instance of GbsSessionParameters and registers it with GBSM The new session description is added to the Session Browser To change a session parameters object select the name of the parameters object in the upper left pane of the Session Browser and use the browser s Edit button to open a Session Parameters Editor Use the Session Parameters Editor to change existing session parameters clicking on OK causes your changes to take effect Removing Session Parameters To remove a GemStone session parameters object from the Session Browser select the session parameters defining the session in the upper left pane of the Session Browser and click on Remove
161. er objects you don t want to share For example you could choose to make a collection shared but keep the existing elements private allowing other developers to add elements but not modify the elements you have already created GemStone s use of segments to control authorization is an efficient way to maintain flexibility and simplicity in managing object access It allows you to change authorization by changing the segment rather than having to make changes to individual objects GemStone Systems Inc March 2006 Security and Object Access Sharing Access to Objects Making Objects Accessible Through Symbol Lists In setting up a UserProfile the data curator initially includes in each user s symbol list the dictionaries that define the names of all the objects he or she believes that user would need Initially each user s symbol list generally includes at least e a Globals dictionary that defines the GemStone kernel classes and any other global objects e a Published dictionary for globally visible shared objects e a private UserGlobals dictionary in which the user can store objects defined for his or her own use Your symbol list tells the GemStone Smalltalk compiler which of many possible GemStone dictionaries to search through to find an object named in your program and determines the order in which to search them Unless a variable is local or is defined in a method s class the GemStone Smalltalk compiler
162. ered with GBSM The lower pane shows all sessions currently logged in To change the current session select a logged in session in the lower pane and click the Current button Logging Out of a GemStone Session With the Session Browser To log out of GemStone from the Session Browser select the session in the browser s lower pane and click on Logout in the row of buttons at the bottom of the browser Before logging out GemBuilder prompts you to commit your changes if the GbsConfiguration setting confirm is true it is true by default If you log out after performing work and do not commit it to the permanent repository the uncommitted work you have done will be lost If you have been working in several sessions be sure to commit only those sessions whose changes you wish to save 2 6 Session Dependents An application can create several related components during a single GemBuilder session When one of the components commits aborts or logs out the other components can be affected and so may need to coordinate their responses with each other In the GemBuilder development environment for example you can commit by clicking on a button in the Session Browser But before the commit takes place all other session dependent components are notified that a commit is about to occur So a related application component such as an open browser containing modified text prompts you for permission to discard its changes before allowing the co
163. ersion Browser For the most part the Class Version Browser s menus are the same as the menus in the Class Browser However the Class Version Browser s Classes menu contains the additional items inspect instances and migrate instances Also March 2006 GemStone Systems Inc 10 7 The Class Version Browser GemBuilder User Manual note that the Classes menu items Move and Remove behave differently in this browser The layout of the browser is similar to the Class Browser The Method Category and Message menus are the same as in a spawned Class Browser The Classes menu however has additional functionality The commands available in the Class Version Browser are shown in Table 10 1 Table 10 1 Class Menu in Class Version Browser file out as Writes GemStone Smalltalk code defining the selected class version and all of its methods to be written to a file in Topaz format The class and its methods can later be re created read from the file and recompiled by means of a command given from the File List Browser See Saving Class and Method Definitions in Files on page 3 18 file out methods as Writes GemStone Smalltalk code defining the selected class version s methods to be written to a file in Topaz format See Saving Class and Method Definitions in Files on page 3 18 for more information on filing out browse class Opens a Class Browser that includes only the sel
164. eryCommit The session with which this object is registered has received a request to commit Return true to allow the commit to take place or false to prevent it queryAbort The session with which this object is registered has received a request to abort Return true to allow the abort to take place or false to prevent it queryEndSession The session with which this object is registered has received a request to terminate the session Return true to allow the logout to take place or false to prevent it Example 2 3 shows how a session dependent might implement an updateRequest method 2 14 GemStone Systems Inc March 2006 Communicating with the GemStone Object Server Session Dependents Example 2 3 updateRequest aspect The session I am attached to wants to do something Return a boolean granting or denying the request queryAbort queryCommit queryEndSession includes aspect ifTrue My session wants to commit or abort OK unless user doesn t want to self askUserForPermission ifFalse Let any other action occur true After the action is performed the sessionsends self changed witha parameter indicating the type of action performed This causes the session to send an update message to each of the registered dependents with one of the following aspect symbols committed All registered objects have approved the request to commit and the transaction has been successfully com
165. ess That Gem is called a linked session When running linked an application and its Gem must run on the same machine and the runtime code requires additional memory An RPC session offers more flexibility because the application and its Gem are separate processes that can run on different hosts in a network Any GemBuilder client can create RPC sessions Where a linked session is supported an application can create multiple sessions but only one can be linked To suppress linked sessions forcing all Gems to run as RPC processes you can load the RPC only version of the shared libraries Figure 2 1 shows an application with two logged in sessions Gem A is a linked session sharing the client Smalltalk application s process space while Gem B is an RPC session running as a separate process March 2006 GemStone Systems Inc 2 3 Session Control in GemBuilder GemBuilder User Manual Figure 2 1 RPC and Linked Gem Processes Client Smalltalk Application Gem Process A linked session Gem Process B RPC session Stone monitor process Object Repository GemStone Object Server 2 3 Session Control in GemBuilder Managing GemStone sessions involves many of the same activities required to manage user sessions on a multi user computer network To manage GemStone sessions you need to do various operations e Identify the object server to which you wish to connec
166. esses the instance variables of the argument If your application uses an object as an argument to a primitive you must either prevent that object from ever becoming a stub or ensure that it is replicated before the primitive is executed To cause a stub to become a replicate send it the message fault Stubs respond to this message by replicating replicates return sel The message faultToLevel allows you to fault in several levels at once as specified To prevent a replicate from ever being a stub configure it as a replicate at login and set its faultPolicy to immediate Defunct Stubs Faulting in a stub relies on the existence of a valid GemStone server object to replicate or forward to If an object is stubbed and the session logs out a message to that stub raises an error complaining that it is defunct For example suppose MyGlobal is modified in the server thereby stubbing it in your client session If the session logs out before MyGlobal is faulted back in the client Smalltalk dictionary contains a defunct stub Because GemBuilder cannot safely assume that a given object will retain the same object identifier from one session to the next it cannot simply fix the problem at next login That s the job of a connector to reestablish at login the stub s relationship to GemStone A connector can do so either directly by connecting the stub itself or transitively by connecting some object that refers to the stub If you
167. ession connectors DataCurator on gemserver61 Type Client Server a Fast GbsObject specialN amed HD Array Fast GbsObject specialN amed HD Association Fast GbsObject specialNamed HOB ag Fast GbsObject specialN amed HOBlockClosure Fast GbsObject specialN amed HOBoolean Fast Byte rray GbsObject specialNamed HOByteArray Y lt gt Postconnect Action C Global verification Connected C Remove bad connectors i Disconnected 6 16 GemStone Systems Inc March 2006 Connectors Making and Managing Connectors The Group Pane The top pane is the Group pane it allows you to select either global connectors or those associated with an individual session Global connectors are predefined to connect the GemStone server kernel classes with their client Smalltalk counterparts When you select an item in this pane the connectors defined for the selected item appear in the middle pane In the Group pane the popup menu provides the following items Table 6 1 Group List Menu in the Connector Browser update Refreshes the views and updates the browser useful if you have made changes in other windows and need to synchronize the browser with them initialize available only when Global Connectors are selected Allows you to remove all connectors except those that connect kernel classes The Connector Pane The middle pane is the Connector pane it lists the connectors their types and
168. exception handler and causes the exception to be signaled GBSM evaluate System signal 10 args 46 signalDictionary MyErrors on GbsGemStoneError do ex ex return handled To explicitly handle your new error in client Smalltalk you first need to associate the GemStone error number with a client exception class Create a new class which should inherit from GbsGemStoneError In this example the class MyNewError GemStone Systems Inc March 2006 Exception Handling Handling Exceptions has been created and this code associates this class with the GemStone error number GbsError defineErrorNumber 10 class MyNewError Then to explicitly handle your new error from client Smalltalk Example 9 4 GBSM evaluate System signal 10 args 46 SignalDictionary MyErrors on MyNewError do ex ex return handled You can obtain the exception s error description string by sending it description For example GBSM execute a at 2 on GbsObjErrBadOffsetIncomplete do ex ex return ex description You can obtain the array of server exception arguments by sending serverArguments to the client exception This array contains client replicates of the server error arguments For example GBSM execute a at 2 on GbsObjErrBadoOffsetIncomplete do ex ex return ex serverArguments For information on how to create Gem
169. fault migration mechanism that copies data from each instance variable of the old object to the instance variable of the same name in the new object if one exists You can write methods to customize this migration on a class by class basis When an object is migrated it refers to the class and class instance variables that have been defined for the new version of the class These variables have whatever values have been assigned to them in the class object The simplest way to retain the data held in instance variables is to use instance variables having the same names If two versions of a class have instance variables with the same name the values of those variables are automatically retained when the instances migrate from one class to the other 10 4 GemStone Systems Inc March 2006 Schema Modification and Coordination Schema Modification However the structure of the two classes may be different and a one to one mapping may not be possible For example if the new class has an instance variable for which no corresponding variable exists in the old class that instance variable is initialized to nil upon migration Similarly if the old class has an instance variable for which no corresponding variable exists in the new class the value of the old variable is dropped and the data it represents is no longer accessible from that object You may encounter situations in which you want to initialize a variable having one name
170. fined results Table 5 1 Delegate Conversion Protocol Message Return Value copy shallow copy of delegate asLocalObject replicate asGSObject self asForwarder undefined beReplicate undefined fault undefined stubYourself undefined Table 5 2 Forwarder to the Server Conversion Protocol Message Return Value copy copies associated server object and returns replicate of copy March 2006 GemStone Systems Inc 5 39 Converting Between Forms GemBuilder User Manual Table 5 2 Forwarder to the Server Conversion Protocol Table 5 3 Table 5 4 Message asLocalObject asGSObject not recommended for customer applications asForwarder beReplicate fault stubYourself Return Value undefined associated delegate self self which has become a replicate self use beReplicate to make a replicate self Replicate Conversion Protocol Message copy asLocalObject asGSObject not recommended for customer applications asForwarder beReplicate fault stubYourself Return Value shallow copy of delegate not associated with any server object undefined associated delegate self which has become a forwarder self self whose instance variables are now also replicates to the configured fault level self which has become a stub Stub Conversion Protocol Message copy asLocalObject asGSObject not recommended for customer applications asForwarder beReplicate fault Return Value sha
171. fying an Existing Class on page 3 15 explains how to create different versions of a class in GemBuilder Instance Migration Within GemStone The migration operation in GemStone is flexible and configurable e Instances of any class can migrate to any other as long as they share a class history The two classes need not be similarly named or have anything else in common e Migration can occur whenever you want it to e You don t have to migrate all instances of a class at once you can migrate only certain instances as needed 10 2 GemStone Systems Inc March 2006 Schema Modification and Coordination Schema Modification e You can choose which values of the old instance variables are used to initialize values of the new instance variables overriding the default mapping mechanism as necessary Setting the Migration Destination You can use the message migrateTo to set a migration destination in the class that you need to migrate from as follows OldClass migrateTo NewClass This message merely lets the class know its migration destination it does not cause migration to occur Migration takes place only when the class receives one of the migrateInstances messages described in the section Migrating Objects It is not necessary to set a migration destination ahead of time you can specify the destination class when you decide to migrate instances It is also possible to set a migration destination and th
172. gning a GemStone Application an Overview GemBuilder User Manual However you might want the classes and methods used to build the report to be stored in GemStone so that others can use them Certain objects can be considered your organization s business objects Business objects contain the data that give your organization its strategic competitive advantage their instance variables contain information about the business process that they model and their methods represent actions involved in conducting business Keeping your business objects centralized and stored separately from the applications that access them allows your organization to serve the needs of all users while still enforcing consistency and maintaining control of critical information Which objects should be secured What security challenges does the application pose Determine the strategy you will use to handle those challenges Does access to certain objects need to be restricted to only certain authorized users Many of your business objects may fall into this category If so who should be authorized to access them and how Do your users fall into groups with different access needs Will anyone need to execute privileged methods The earlier you lay the groundwork for your security needs the easier they will be to implement Security is discussed in detail in Chapter 8 Which objects should be connected Once you ve decided how to partition your application obj
173. h 2006 GemBuilder User Manual dirty defined 5 10 disabling automatic class generation 5 5 block replication 5 32 Disconnected command in Connector Browser 6 6 6 19 domain objects 1 8 dumpAllProcessStacks GbsConfiguration 4 10 E error user defined 9 4 error handling during file in 3 20 in client Smalltalk and in GemStone E 2 evaluate 5 37 evaluate context 5 38 event polling for A 5 eventPollingFrequency configuration parameter A 2 A 5 eventPriority configuration parameter A 2 A 5 examining the internal structure of a GemStone object 4 2 exception handling 9 1 9 5 see error handling exclusiveLock GbsSession 7 13 exclusiveLock ifDenied ifChanged GbsSession 7 13 exclusiveLockAl11 GbsSession 7 13 exclusiveLockAl1 ifIncomplete GbsSession 7 14 execution in GemStone 11 6 in the client Smalltalk 11 6 profiling 11 2 tuning 11 6 11 8 explicit stubbing of objects to reclaim space 11 10 F fast connector 6 9 fault 5 21 fault control and replicates 11 8 and stubs 11 8 fault level defined 5 17 performance and 11 8 specifying with replication specification 5 20 fault policy defined 5 20 faulting at login 5 18 changes from other sessions 5 19 cost of 11 8 customized 5 27 5 31 customizing a class 5 22 default policy for A 5 dirty GemStone objects 11 7 immediate 5 20 inadequate penalties of 11 8 lazy 5 20 minimizing for performance
174. he GemStone log file Looking at log messages will show you the way an NRS works For example Opening transaction log file for read filename tcp oboe dbf userl gemstone data tranlog0 dbf An NRS can contain spaces and special characters On heterogeneous network systems you need to keep in mind that the various UNIX shells have their own rules for interpreting these characters If you have a problem getting a command to work with an NRS as part of the command line check the syntax of the NRS recorded in the log file It may be that the shell didn t expand the string as you expected NOTE Before you begin using network resource strings make sure you understand the behavior of the software that will process the command See each operating system s documentation for a full discussion of its own rules For example under the UNIX C shell you must escape an exclamation point with a preceding backslash character waitstone tcp oboe gemserver61 1 If there is a space in the NRS you can replace the space with a colon or you can enclose the string in quotes For example the following network resource strings are equivalent waitstone tcp oboe auth user password gemserver61 waitstone tcp oboe auth user password gemserver61i C 2 Defaults The following items uniquely identify a network resource e communications protocol TCP IP e destination node the host that has the resource e authent
175. he Group menu Enter the group name in the dialog box that appears If the group does not exist in the repository you will be asked whether to create it 8 18 GemStone Systems Inc March 2006 Security and Object Access GemStone Administration Tools To remove a group from the authorization list first select the group by clicking in the first column of the groups list Then choose Remove from the Group menu You will be asked to confirm the action To change the type of access for a particular group first select that group in the groups list and select the existing permission Then enter the new permission read or write To add a member to a group that has access to this segment first select that group in the groups list Then choose Add from the Member menu Enter the Userld and choose OK A UserProfile with that Userld must already exist in the repository To remove a member from a group that has access to this segment select the Userld in the member list and choose Remove from the Member menu You will be asked to confirm the action Remember to commit your transaction before logging out A convenient way to do that is by choosing Commit from this tool s File menu Changing a User s Default Segment You must either have DefaultSegment privileges to change your own default segment or have write authorization in the DataCurator Segment to change another user s default segment To chang
176. he entire hierarchy of BigDictionary at login users will experience unacceptable network delays and the client Smalltalk image can t handle data sets as large as the GemStone server can Furthermore it s unnecessary only a small number of objects will be needed for the current task To help prevent this kind of over replication GemBuilder provides stubs A stub like a forwarder is also a proxy associated with a server object Unlike a forwarder however when a stub receives a message it does not send the message across to the other object space Instead it faults is server counterpart into the client image The client Smalltalk replicate then responds to the message When GemBuilder faults automatically it replicates the object hierarchy to a certain level then creates stubs for objects on the next level deeper than that The number of levels that are replicated each time is the fault level March 2006 GemStone Systems Inc 5 17 Replicates GemBuilder User Manual A fault level of 1 follows an object s immediate references and faults those in A fault level of 2 follows one more layer of references and replicates those objects too Figure 5 1 illustrates an application with a fault level of 2 Faulting at Login At login the connectors connect and objects a b and C are replicated objects d and e are stubbed objects f and g are ignored Figure 5 1 Two level Fault of an Object Client Smalltalk GemSt
177. he object server and user account to which you wish to connect This information is stored in an instance of GbsSessionParameters and added to a list maintained by GBSM You can provide the information through window based tools or programmatically Both methods are described in later sections In either case you must supply these items The name of the GemStone repository For a Stone running on a remote server be sure to include the server s hostname in Network Resource String NRS format For instance for a Stone named gemserver61 on a node named pelican specify an NRS string of the form pelican gemserver61 Appendix C describes NRS syntax in detail GemStone user name and GemStone password This user name and password combination must already have been defined in GemStone by your GemStone data curator or system administrator GemBuilder provides a set of tools for managing user accounts see User Account Management Tools on page 8 23 Because GemStone comes equipped with a data curator account we show the DataCurator user name in many of our examples March 2006 GemStone Systems Inc 2 5 Session Control in GemBuilder GemBuilder User Manual Host username and Host password not required for a linked session or if netldi is run in guest mode This user name and password combination specifies a valid login on the Gem s host machine the network node specified in the Gem service name descri
178. hen choosing the space in which to execute methods Relative Platform Speeds One consideration when choosing the execution platform is the relative speed of the client Smalltalk and the server Smalltalk execution environments Your client Smalltalk will often run faster than GemStone on the same machine GemStone s database management functions and its ability to handle very large data sets add some overhead that the client Smalltalk environment doesn t have Cost of Data Management Execution cannot complete until all objects required have been brought into the object space When executing in the client Smalltalk this means that all GemStone server objects required by the message must be faulted from GemStone When executing in GemStone this means that dirty replicates must be flushed from the client Smalltalk In general it is impossible to tell exactly which objects will be required by a message send so GemBuilder flushes all dirty replicates before a GemStone message send and faults all dirty GemStone server objects after the send Clearly data movement can be expensive Although the client Smalltalk environment might be more efficient for some messages faulting the object into the client Smalltalk might overwhelm the savings If the objects are all already there however or if the objects will be reused for other messages then the movement may be justified For example consider searching a set of employees for a specific empl
179. horization Segment The SystemRepository object initially has three instances of class Segment associated with it e the SystemSegment owned by the SystemUser e the DataCuratorSegment owned by the DataCurator and e the GcUser s Segment owned by the GcUser A segment has no physical basis it is not a location It is merely a logical entity that serves as a means of controlling ownership of and access to objects New segments can be added to the SystemRepository when new users are added Each segment has a single owner and stores a reference to the owner s UserProfile Figure 8 1 shows the relationship between the classes Repository Segment and UserProfile 8 4 GemStone Systems Inc March 2006 Security and Object Access Classes for Controlling Access to Objects Figure 8 1 GemStone s Object Level Security Mechanism Segment itsRepository itsOwner groupsRead groupsWrite ownarAuthonzation UserProfile Repository worldAuthorization ryptedPassword nang spare 1 userld dataDictionary symbolList Segment 1 defaultSegment Segment2 privileges Segment 3 groups spare1 spare2 spare3 compilerLanguage Each segment associated with the SystemRepository contains instance variables that refer to its repository its owner the groups that are authorized to read and or write objects that are assigned to it and the level of authorization for the segment s owner an
180. iable means that its value is always either an instance of the specified class a subclass thereof or nil Constraints are not supported in GemStone S 64 Bit 3 10 GemStone Systems Inc March 2006 Using the GemStone Programming Tools Coding Constraints can be circular you can constrain an instance variable to be an instance of its own class or you can also constrain instance variables of two classes to each hold instances of the other Constraints are inherited when you define a subclass its inherited instance variables by default bear the same constraints as those specified in their superclass However inherited instance variables can be further constrained in a subclass In this case the instance variable s new constraint must be a subclass of that specified by the inherited constraint To further constrain inherited instance variables specify the name of the inherited variable and its new constraint in the argument to the constraints keyword in the class definition template For example suppose you have defined a class Employee with instance variables named jobTitle and department that are constrained to be Strings You can now create a subclass of Employee named FormerEmployee and constrain the inherited variables jobTitle and department to be InvariantStrings FormerEmployee s new instance variables can be constrained or not as you require and its other inherited instance variables retain whatever constraints we
181. ication of the user such as a system authorization code e resource type such as server database extent or task e environment such as a NetLDI a directory or the name of a log file e resource name the name of the specific resource being requested GemStone Systems Inc March 2006 Network Resource String Syntax Notation A network resource string can include some or all of this information In most cases you need not fill in all of the fields in a network resource string The information required depends upon the nature of the utility being executed and the task to be accomplished Most GemStone utilities provide some context sensitive defaults For example the Topaz interface prefixes the name of a Stone process with the server resource identifier When a utility needs a value for which it does not have a built in default it relies on the system wide defaults described in the syntax productions in Syntax on page C 4 You can supply your own default values for NRS modifiers by defining an environment variable named GEMSTONE_NRS_ALL in the form of the nrs header production described in the Syntax section If GEMSTONE_NRS_ALL defines a value for the desired field that value is used in place of the system default There can be no meaningful default value for resource name A GemStone utility picks up the value of GEMSTONE_NRS_ALL as it is defined when the utility is started Subsequent changes to the envir
182. ich objects to associate using connectors Connecting and Disconnecting describes what connectors do and when they do it Kinds of Connectors describes the available kinds of connectors and the differences between them March 2006 GemStone Systems Inc 6 1 Connecting Root Objects GemBuilder User Manual Making and Managing Connectors explains how to use connectors in code or using the Connector Browser 6 1 Connecting Root Objects Every replicate and forwarder in the client is connected to an object in the server You do not however need a connector for every replicate or forwarder A typical application only needs connectors for a small number of root objects A connector connects more than the specified client object to the specified server object through transitive reference a connector connects whole networks of objects Most objects except atomic objects characters booleans small integers nil refer to others through their instance variables And their instance variables refer to their instance variables and so on branch and twig until you reach the leaves of a large network of objects with a treelike structure You can take advantage of this hierarchical structure to minimize application overhead Identify the object at the root of each subsystem of shared objects and then connect only these root objects Depending on how you ve defined configuration parameters and related matters you can synchronize entir
183. id to commit the transaction To commit a transaction from the client send the message aGbsSession commitTransaction to commit a specific session or GBSM commitTransaction to commit the current session or in the Session Browser select the session and click on the Commit button or in the Class Browser use the pop up menu on the SymbolDictionary pane to select commit When the commit succeeds the method returns true Successfully committing a transaction has two effects e It copies the application s new and changed objects to the shared object repository where they are visible to other users e Itrefreshes the application s private GemStone view by making visible any new or modified objects that have been committed by other users A commit request can be unsuccessful in two ways e A commit fails if the object server detects a concurrency conflict with the work of other users When the commit fails the commitTransaction method returns false e Acommit is not attempted if a related application component is not ready to commit When the commit is not attempted the commitTransaction method returns nil See Session Dependents on page 2 13 GemStone Systems Inc March 2006 Managing Transactions Operating Inside a Transaction In order to commit the session must be operating within a transaction An attempt to commit while outside a transaction raises an exception Aborting a Transaction
184. implement the copyEmpty method to ensure that added instance variables are included in the copy operation Failure to reimplement copyEmpty results in data loss For example consider a Collection subclass called MyCollection that defines the additional instance variable name with methods name and name that retrieve and assign its value respectively MyCollection might reimplement copyEmpty like this MyCollection gt gt copyEmpty size super copyEmpty size name name This reimplementation of copyEmpty preserves the copying behavior of the superclass and assures that the added instance variable is also copied 5 5 Precedence of Replication Mechanisms Certain replication mechanisms can appear to contradict each other The rules of precedence are e Ifthe class methods instVarMap for replicates or instancesAreForwarders for forwarders are implemented they take precedence over all others and are always respected e Otherwise if the class method replicationSpec is implemented or if an application calls or replicationSpecSet to switch among several replication specs those replication specs take precedence In other words if a class implements a replication spec but it also implements instancesAreForwarders to return true then instances of that class will be forwarders and the replication spec will be ignored 5 36 GemStone Systems Inc March 2006 Sharing Objects Evaluating Smalltalk Code on the Gem
185. ins a reference to that session s parameters which you can retrieve by sending myGbsSessionParameters aGbsSession parameters GBSM maintains a collection of currently logged in GbsSessions You can determine if any sessions are logged in with GBSM isLoggedIn and you can execute GBSM loggedInSessions to return an array of currently logged in GbsSessions 2 10 GemStone Systems Inc March 2006 Communicating with the GemStone Object Server Logging In To and Logging Out Of GemStone The Current Session When a new GbsSession is created it is registered with GBSM which maintains a variable that represents the current session When a session logs in it becomes the current session If you execute code in a GemStone tool the code is evaluated in the session that was current when you opened that tool If you send a message to GBSM that is intended for a session the message is forwarded to the current session You can send a message directly to any logged in GbsSession even when it is not the current session If you send a specific session a message that executes code that code is evaluated in the receiving session regardless of whether it is the current session Most applications have only one session logged in at a time In this case that session will always be the current session and it is safe to send messages to GBSM for forwarding to the session However if your application concurrently logs in more than on
186. ints name String address Address Step 11 After the instancesInvariant keyword specify whether instances of the class are modifiable The default is alse change this to true if you wish instances to be invariant Step 12 After the isModifiable keyword specify whether the structure of the class can be modified The default value is fal se change this to true if you wish class to be invariant Step 13 Accept or save your changes and commit your transaction to make the class part of the repository NOTE You cannot subclass certain GemStone kernel classes To determine which ones execute the method subclassesDisallowed against the class Object The method returns true for any class that you cannot subclass For example consider the following definition of a class named Employee March 2006 GemStone Systems Inc 3 13 Coding GemBuilder User Manual Example 3 1 Object subclass Employee instVarNames name employeeNum jobTitle department address classVars classInstVars poolDictionaries inDictionary UserGlobals Employee resides in the developer s UserGlobals dictionary constraints name String employeeNum SmalliInteger jobTitle String department Symbol address Address For efficient access constraints have been placed on each instance variable name must be an instance of String emp loyeeNum must be an instance of
187. ion classes These classes can be found in the application package GbsExceptions In VisualWorks these exception classes are defined in the namespace GemStone Gbs On the GemStone server there is a dictionary of error names called ErrorSymbols This dictionary lists all the errors that can occur when communicating with a GemStone session For each of these errors there is a corresponding client exception class The name of that class is derived by making the first character of the error symbol uppercase and prepending Gbs So for instance the server error rtErrBadArgKind corresponds to the client exception class GbsRtErrBadArgKind The GemBuilder exception classes fit into the VisualWorks exception hierarchy as shown below GenericException ControlInterrupt GbxAbstractControlInterrupt lt various specific error classes related to pauses breaks or breakpoints gt Exception Error GbxAbstractException GbsGemStoneError GbsAbortingError lt various specific error classes that cause aborts gt GbsCompilerError lt various specific compile related error classes gt GbsEventError lt various specific signal related error classes gt GbsFatalError lt various specific fatal error classes gt GbsInterpreterError lt various specific other error classes gt GbsInterfaceError GbsAssertionError GbsBlockReplicationError GbsClassGenerationError GbsConnectorError GbsLinkedLoginError GbsNotCachedError GbsUnsuppo
188. ion time is being spent There are client Smalltalk tools available for profiling client code GemStone also has a profiling tool in the class ProfMonitor This class allows you to sample the methods that are executed in a given block of code and to estimate the percentage of total execution time represented by each method within GemStone server execution See the chapter on performance in the GemStone Programming Guide for details Profiling Client Smalltalk Execution GemBuilder can be configured to collect statistics describing the performance of its internal operation These statistics are archived to a file a statistics archive file which can be viewed by a tool called VSD for more information on VSD See VSD on page 11 6 Statistics tracking introduces minimal overhead into GBS A VisualWorks process named GBS Stat Monitor samples and archives the stats at a regular configurable time interval To enable the tracking of all GBS statistics in an image and start the statistics monitor archiving at a default interval of once every 2000 milliseconds execute the following GBSM statsEnabled true To disable all statistics tracking and turn off the statistics monitor execute GBSM statsEnabled false To check if any statistics are currently enabled GBSM statsEnabled 11 2 GemStone Systems Inc March 2006 Performance Tuning Profiling Main Statistics GBS provides two groups of
189. irect assignment however does not cause the stub to be faulted in and can cause errors self stubYourself self instVarX 5 reliable self stubYourself instVarX 5 unreliable Using Forwarders Another solution is to declare the setOfEmployees as a forwarder See Forwarders on page 5 6 11 5 Using Primitives Sometimes there is an advantage to dropping out of Smalltalk programming and writing methods in a lower level language such as C Such methods are called primitives in Smalltalk GemStone refers to them as user actions There are serious concerns when doing this In general such applications will be less portable and less maintainable However when used judiciously there can be significant performance benefits In general profile your code and find those methods that are heavily used to be candidates for primitives or user actions The trick to proper use of primitives or user actions is to create as few as possible Excess primitives or user actions make the system more difficult to understand and place a heavy burden on the maintainer March 2006 GemStone Systems Inc 11 11 Changing the Initial Cache Size GemBuilder User Manual For a description about adding primitives to your client Smalltalk see the vendor s documentation For adding user actions to GemStone see the GemBuilder for C user manual To load the user action in client Smalltalk execute GBSM loadUserActionLibrary
190. ject being stored or an instance of GbsBuffer sized to match the number of named instance variables in the client object The store operations then access this buffer for storing in the server indexableValues Implement this to return a list of the indexable instance variables in the client object The store operations then access this list for storing in the server Implementations of namedValues must return an object with the appropriate number of named instance variable slots In Example 5 7 a clone of the positionable stream is returned that increments the position instance variable by 1 as needed when mapped into the server Example 5 7 PositionableStream gt gt namedValues aClone aClone self copy aClone instVarAt 1 put self contents aClone instVarAt 2 put position 1 aClone March 2006 GemStone Systems Inc 5 29 Replicates GemBuilder User Manual An alternative might return an instance of GbsBuffer a subclass of Array of the appropriate size A special buffer class is necessary to distinguish between trying to store an array and trying to store the named values of an object residing in a buffer The default implementation of namedValues is to return self In this case the instance variables are processed directly from the object being stored eliminating the need for a temporary array Implementations of indexableValues must return an indexable collection containing a sequential
191. jects may differ from their precommit state e The current transaction is still in effect However you must end the transaction and start a new one before you can successfully commit e Temporary Smalltalk objects remain unchanged March 2006 GemStone Systems Inc 7 5 Operating Outside a Transaction GemBuilder User Manual e Modified GemStone server objects remain unchanged Unmodified GemStone server objects are updated with new values from the shared repository Following a commit failure your session must refresh its view of the repository by aborting the current transaction The uncommitted transaction remains in effect so you can save some of its contents if necessary before aborting A common strategy for handling such a failure is to abort then reinvoke the method in which the commit occurred Depending on your application you may simply choose to discard the transaction and move on or you may choose to remedy the specific transaction conflict that caused the failure then initiate a new transaction and commit If you want to know why a transaction failed to commit you can send the message aGbsSession transactionConflicts This expression returns a symbol dictionary whose keys indicate the kind of conflict detected and whose values identify the objects that incurred each kind of conflict See Managing Concurrent Transactions on page 7 10 for more discussion of the kinds of conflicts that can arise
192. keys of the entries in the dictionary are displayed in the Entries pane on the right Whenever a dictionary or an entry is selected information about that object is displayed at the bottom of the browser The Clipboard Within the Symbol List Browser you can delete move and copy objects to and from SymbolLists and the Dictionaries in those SymbolLists For each session to which a Symbol List Browser is attached there is a clipboard onto which GemStone server objects can be cut and copied and from which objects can be pasted into another Symbol List Browser that is also attached to that session Symbol List Browser Menus Table 8 6 The menus in the symbol list browser allow you to examine add and delete SymbolLists dictionaries and dictionary entries You can use this browser to copy references to dictionaries and dictionary entries among user accounts so application objects can be shared by other users File Menu The File menu contains items for operating on the window itself and for committing and aborting transactions from the Symbol List Browser File Menu in the Symbol List Browser Commit Makes all changes in the current transaction permanent Abort Aborts the current transactions Update Updates the browser s view of the GemStone server objects it shows The browser is automatically updated if the attached session aborts a transaction Close Close the browser Any changes are retained in
193. lamp isClientF orwarder is false unexport isSpecial is false isGSDefunct is false h Clamp state unknown basic gsOop Delegate scheduled for unexport at GC flags GS Exported uncached oop scheduled not unexport candidpte Not in session cache client export When inspecting an object that has a corresponding GemStone server object the inspector allows you to view both the client object and the server object in the same inspector Client objects with corresponding server objects includes replicates of server objects forwarders to server objects stubs and objects that are always mapped such as nil true false SmallIntegers and Characters When you are inspecting one of these objects you will see two sets of tabs one that allows you to examine the client object and a second similar set of tabs with the GS prefix to examine the associated GemStone server object March 2006 GemStone Systems Inc 4 3 Inspectors GemBuilder User Manual Figure 4 3 Inspector on a Replicate ala Object Edit Go History Explore Tools Help col ass ae Elements Basic Methods Gs Elements Gs Basic GS Delegate a gt aaa bbb 23 In the evaluation pane of the inspector or any other pane the use of self is resolved according to the following rules e Do it Print it Inspect it and Debug it resolve self to the client object e GS Do it GS Print it GS Inspect it and GS De
194. lder User Manual stubYourself 5 20 11 10 subclassing 3 12 superclass specifying name of 3 12 symbol dictionaries 8 20 Symbol List Browser 8 9 8 10 8 20 8 23 copying and pasting objects 8 21 Dictionaries pane 8 20 File menu 8 21 Symbol List pane in GemStone Browser 3 5 symbol lists 8 9 as client and GemStone objects 5 10 5 14 and at put 5 12 and basicAt put 5 12 instances of kernel classes 5 14 shared objects 6 18 SystemRepository segments in 8 12 T tools attached to current session 2 12 overview 1 6 transaction 7 1 7 19 aborting 7 5 committing 1 4 and performance 7 16 committing and session dependents 2 13 managing 2 13 7 2 7 4 modes 7 8 7 10 automatic 7 8 7 9 automatic defined 7 8 manual 7 9 manual defined 7 9 switching between 7 9 transactionless 7 2 transactionless transaction mode 7 2 transient object stubs preventing 11 9 transitive closure 6 4 transparency and access to GemStone 1 4 and kernel classes 5 14 traversal buffer compressing for transmission traversalBufferSize method 11 9 traversalBufferSize configuration parameter 11 9 A 2 A 8 traversalCompression configuration parameter A 2 A 8 U updateRequest 2 14 updating class definitions 5 4 replicate 5 9 User Account Management Tools 8 10 GemStone User Dialog 8 25 8 26 GemStone User List 8 23 Privileges Dialog 8 27 user actions 11 11 and primitives 11 11 UserClasses symbol dictionary 5 5 user defined
195. le when using different server products This manual primarily documents behavior with the GemStone S 6 x server product Please consult the documentation for the server product and version you are using for specific details on that product March 2006 GemStone Systems Inc 111 GemBuilder User Manual Prerequisites To make use of the information in this manual you need to be familiar with the GemStone object server and with GemStone s Smalltalk programming language as described in the GemStone S Programming Guide That book explains the basic concepts behind the language and describes the most important GemStone kernel classes In addition you should be familiar with the VisualWorks Smalltalk language and programming environment as described in the VisualWorks Smalltalk product manuals Finally this manual assumes that the GemStone system has been correctly installed on your host computer as described in the GemStone S System Administration Guide and that your system meets the requirements listed in your GemBuilder for Smalltalk Installation Guide How This Manual is Organized Chapter 1 Basic Concepts describes the overall design of a GemBuilder application and presents the fundamental concepts required to understand the interface between client Smalltalk and the GemStone object server Chapter 2 Communicating with the GemStone Object Server explains how to communicate with the GemStone object server by initiating
196. lient counterpart out of date the server object is now dirty This can occur during execution of server Smalltalk or at a transaction boundary when changes committed by other sessions become visible to your session When the state of dirty server objects is transferred to their corresponding client objects this is called faulting Together GemBuilder and the GemStone server manage the timing of faulting and flushing Faulting GemBuilder faults objects automatically when required Faulting is required when a stub receives a message requesting it to turn itself into a replicate see stubbing on page 5 17 Faulting may also be required when e Connectors connect this typically occurs at login the beginning of a GemStone session but you can connect and disconnect connectors explicitly during the course of a session using either code or the Connector Browser Faulting may or may not occur upon connection depending on the post connect action specified for the connector 5 10 GemStone Systems Inc March 2006 Sharing Objects Replicates Flushing e A server object that has been replicated to the client is modified on the server This can happen in two cases 1 GemStone Smalltalk execution in your session modifies the state of the object GemStone Smalltalk execution occurs when a forwarder receives a message or in response to any variant of GbsSession gt gt evaluate 2 Your session starts commits aborts or conti
197. list of the elements in the collection In Example 5 8 for class Set an Array is returned because the indexable fields of a Smalltalk set are a sparse list of the actual elements Example 5 8 Set gt gt indexableValues values index values Array new self size index 1 self elementsDo each values at index put each index index 1 values The default implementation of indexableValues is to return sel f In this case the indexable slots are processed directly from the object being stored eliminating the need for a temporary array You can also override the messages indexableValueAt and namedValueat to return processed values rather than the actual values in the indexable and named slots of the object For example OrderedCollection might implement indexableValueAt as OrderedCollection gt indexableValueAt index self at index This lets OrderedCollection control for the fact that its underlying indexable slots are being managed by the first Index and last Index instance variables that is the first actual indexable slot of the object may not necessarily be the first logical element In conjunction with these two methods you might need to reimplement the messages indexableSize and namedSize as well For example to match the 5 30 GemStone Systems Inc March 2006 Sharing Objects Replicates implementation of indexableValueAt above OrderedCollection would have
198. lk setOfEmployees lt p Clearly there can be a large number of objects referenced transitively from the employee set If the application s focus of interest changes from the set to say a specific employee it may make sense to free the object space used by the employee set In this example one solution is to send stubYoursel f to the setOfEmployees All employees except those referenced separately from the set become candidates for garbage collection 11 10 GemStone Systems Inc March 2006 Performance Tuning Using Primitives Of course if the application will be referencing the setOfEmployees again in the near future the advantage gained by stubbing could be offset by the increased cost of faulting later on Also be aware of the difference between two ways of modifying the value of an instance variable by using an access method and by direct assignment For example consider an object with an instance variable named instVarX You can assign the value 5 to instVarX in two ways insVarX 5 direct assignment self instVarX 5 access method When the object is replicated in your Smalltalk workspace each of these assignments yields the same result When the object is represented in the Smalltalk workspace by a stub however the stub must be faulted in as a replicate unstubbed before the assignment can occur The access method causes the stub to be faulted in and yields the correct result D
199. llector GemStone may also be covered by one or more pending United States patent applications TRADEMARKS GemStone GemBuilder GemConnect and the GemStone logos are trademarks or registered trademarks of GemStone Systems Inc in the United States and other countries UNIX is a registered trademark of The Open Group in the United States and other countries Sun Sun Microsystems Solaris and SunOS are trademarks or registered trademarks of Sun Microsystems Inc All SPARC trademarks are used under license and are trademarks or registered trademarks of SPARC International Inc SPARCstation is licensed exclusively to Sun Microsystems Inc Products bearing SPARC trademarks are based upon an architecture developed by Sun Microsystems Inc HP and HP UX are registered trademarks of Hewlett Packard Company Intel and Pentium are registered trademarks of Intel Corporation in the United States and other countries Microsoft MS Windows Windows 2000 and Windows XP are registered trademarks of Microsoft Corporation in the United States and other countries Linux is a registered trademark of Linus Torvalds and others Red Hat and all Red Hat based trademarks and logos are trademarks or registered trademarks of Red Hat Inc in the United States and other countries AIX and POWER4 are trademarks or registered trademarks of International Business Machines Corporation Other company or product names mentioned herein may be trademarks or registered t
200. llow copy receiver becomes a replicate undefined associated delegate self which has become a forwarder self use fault to become a replicate self 5 40 GemStone Systems Inc March 2006 Sharing Objects Converting Between Forms Table 5 4 Stub Conversion Protocol Table 5 5 Message Return Value stubYourself self Conversion Protocol for Unshared Client Objects Message Return Value copy shallow copy asLocalObject undefined asGSObject not new delegate creates new associated server object recommended for customer applications asForwarder self which has become a forwarder creates new associated server object beReplicate self fault self stubYourself self March 2006 GemStone Systems Inc 5 41 Converting Between Forms GemBuilder User Manual 5 42 GemStone Systems Inc March 2006 Chapter Connectors This chapter describes connectors which allow an application developer to explicitly declare an association between a root client object and a root server object e Connectors function at login After that you must manually disconnect and reconnect them to effect any changes e There are different kinds of connectors for different types of objects e Connectors may update either connected object depending on how they are set up Connectors exist either in a given session or globally in every session your image defines Connecting Root Objects explains wh
201. lltalk GemStone s Smalltalk language is very similar to client Smalltalk in both its organization and its syntax GemStone Smalltalk extends the Smalltalk language with classes and primitives to add multiuser features such as transaction support and persistence The GemStone class hierarchy is extensible and new classes can be added as required to model an application The GemStone class hierarchy is described in the GemStone Programming Guide A quick look at the GemStone class hierarchy shows that it differs from the client Smalltalk class hierarchy in that classes for screen manipulation and the client Smalltalk programming environment don t exist and in that the GemStone Smalltalk hierarchy contains classes for transaction control accounting ownership authorization replication user profiles and indexing collections GemStone Smalltalk also introduces constraints and optimized selection blocks As a Smalltalk programmer you will feel quite at home with GemStone Smalltalk but you should take note of the differences outlined in this appendix March 2006 GemStone Systems Inc D 1 GemBuilder User Manual Selection Blocks Selection blocks in GemStone Smalltalk and the use of dots for path notation have no counterparts in client Smalltalk myEmployees select i i is permanent Array Constructors Array constructors do not exist in client Smalltalk In GemStone array constructors e use square brackets
202. lock requests are made with the following statements aGbsSession readLock anObject aGbsSession writeLock anObject aGbsSession exclusiveLock anObject The above messages request a particular type of lock on anObject If the lock is granted the method returns the receiver Lock types are described in the GemStone Programming Guide note that exclusive locks are not available in GemStone S 64 Bit If you don t have the proper authorization or if another session already has a conflicting lock an error will be generated When you request an exclusive lock an error will be generated if another session has committed a change to anObject since the beginning of the current transaction In this case the lock is granted despite the error but it is seen as dirty A session holding a dirty lock cannot commit its transaction but must abort to obtain an up to date value for anObject The lock will remain however after the transaction is aborted Another version of the lock request allows these possible error conditions to be detected and acted on aGbsSession readLock anObject ifDenied blockl ifChanged block2 aGbsSession writeLock anObject ifDenied blockl ifChanged block2 aGbsSession exclusiveLock anObject ifDenied block1 ifChanged block2 If another session has committed a change to anObject since the beginning of the current transaction the lock is granted but dirty and the method returns the value of the zero argument
203. ly state domain objects and application logic reside on server server executes all but user interface code A web based application that uses the client merely to manage the browser needs little functionality on the client and what it does need is cleanly delimited State resides on both client and server client manages most execution server is used mainly as a database A Department of Motor Vehicles could use a repository of driver and vehicle information properly defined for a bevy of fairly straightforward client applications to manage driver s licenses parking permits commercial licenses hauling permits taxation and fines Execution occurs and therefore state resides on both client and server At specified intervals clients of a nationwide ticket booking network download the current state of specific theaters on specific dates Clients book seats and update their local copies of theaters until they next connect to the repository To resolve conflicts server and client engage in a complex negotiation GemStone Systems Inc March 2006 Sharing Objects Class Mapping For these and other solutions GemBuilder provides several kinds of client and server side objects and a mechanism a connector for describing the association between pairs of root objects across the two object spaces Three kinds of objects help a GemBuilder client and a GemStone server repository share state and execution forwarders stubs
204. ly be assigned to radius and angle In this case the appropriate method to override is migrateFrom instVarMap Then when you migrate an instance of Point to an instance of NewPoint the migration code that calls migrateFrom instVarMap executes the method in NewPoint instead of the one in Object that defines the default behavior This example is explained in detail in the GemStone Programming Guide March 2006 GemStone Systems Inc 10 5 Schema Coordination GemBuilder User Manual 10 2 Schema Coordination GemBuilder s goal in supporting schema migration is to provide an interaction between the client Smalltalk and the GemStone server that provides as much of GemStone s capabilities as possible while minimizing the impact on the client Smalltalk system GemBuilder preserves the behavior of having only a single version of a given class in client Smalltalk at one time That client Smalltalk class will be mapped to a specific version of a GemStone server class resolved at login time if a connector is defined by its name If while faulting an object into client Smalltalk GemBuilder discovers that the server object is an instance of a class that is a different version of the class that is in client Smalltalk and the class version of the server object is less than the class version that is already mapped to the client class it will be faulted in in the format of the class in client Smalltalk and flagged so that if it is modifie
205. mStone Smalltalk compiler upon each execution and so have extra overhead Also the inability to pass arguments rules out the evaluate messages for some uses 5 38 GemStone Systems Inc March 2006 Sharing Objects Converting Between Forms Message sends through forwarders are the most common means of initiating execution of GemStone Smalltalk code on the server However a message passed through a forwarder will fail if the server object that receives the message does not understand that message Forwarder sends require previous definition of an appropriate GemStone method on the server The two forms of execution complement each other The evaluate messages do not require prior method definition but cannot take arguments Forwarder sends require prior method definition but can take arguments 5 7 Converting Between Forms A variety of messages exist to convert between delegates forwarders replicates stubs and unconnected client objects Table 5 1 Table 5 5 list the results of sending any of several conversion messages to these objects A delegate is an instance of GbxDelegate Delegates are used internally by GemBuilder An application doesn t normally need to use delegates directly but you may see them when debugging We recommend against using delegate protocol as in Table 5 1 in customer applications NOTE To avoid unpredictable consequences and possible errors do not use the expressions listed as producing unde
206. mStone Smalltalk for recompilation and execution If a block is used more than once GemBuilder saves a reference to the replicated block to avoid redundant compilations March 2006 GemStone Systems Inc 5 31 Replicates GemBuilder User Manual For example consider the use of select to retrieve elements from a collection of Employees fredEmps fredEmps myEmployees select anEmployee anEmployee name Fred If myEmployees is a forwarder to a collection residing in the object server then GemBuilder sends the parameter block s source code anEmployee anEmployee name Fred to GemStone to be compiled and executed Replication of client Smalltalk blocks to GemStone Smalltalk is subject to certain limitations When block replication violates one of these limitations GemBuilder issues an error indicating that the attempted block replication has failed To avoid these limitations consider using block callbacks instead Block callbacks are discussed starting on page 5 35 You can disable block replication completely using GemBuilder s configuration parameter blockReplicationEnabled Block replication is enabled by default Set this parameter to false to disable it and GemBuilder raises an exception when block replication is attempted This can be useful for determining if your application depends on block replication Image stripping Limitations Block replication relies on the clie
207. mit Makes all changes in the current transaction permanent Abort Aborts the current transaction Update Causes the browser to update its view of the GemStone users it shows The browser will automatically be updated if the attached session aborts a transaction Close Close the browser Changes are retained in the image but not committed to the repository 8 24 GemStone Systems Inc March 2006 Security and Object Access GemStone Administration Tools Table 8 10 shows operations available in this dialog Table 8 10 GemStone User List Create User Brings up a GemStone User dialog in which you can define a new user Show User Info Brings up a GemStone User window displaying privilege and group membership information on a selected user Delete User Allows you to remove a user name The Help menu contains one item Session Info which provides information about the session for the GemStone User List and about the current session GemStone User Dialog The GemStone User Dialog displays the attributes of a particular GemStone user The GemStone administrator can examine and change the user s privileges or default segment and can control the user s group membership The administrator can also change the name available in the user s symbol list The GemStone User Dialog is shown in Figure 8 5 March 2006 GemStone Systems Inc 8 25 GemStone
208. mitted aborted All registered objects have approved the request to abort and the transaction has been aborted sessionTerminated The request to log out has been approved and the session has logged out Each registered dependent should be prepared to receive an update message with one of the above aspect symbols as its argument Example 2 4 shows how a session dependent might implement an update method March 2006 GemStone Systems Inc 2 15 Session Dependents GemBuilder User Manual Example 2 4 update aSymbol The session I am attached to just did something I might need to respond aSymbol sessionTerminated ifTrue The session this tool is attached to has logged out close ourself self builder notNil ifTrue self closeWindow Figure 2 4 summarizes the sequence of events that occurs when a session queries a dependent before committing In the figure the Session Browser sends a commit request commitTransaction toa session 1 The session sends updateRequest queryCommit to each of its dependents 2 If every dependent approves returns true the commit proceeds 4 Following a successful commit the session notifies its dependents that the action has occurred by sending update committed to each 5 2 16 GemStone Systems Inc March 2006 Communicating with the GemStone Object Server Session Dependents Figure 2 4 Committing with Approval From a Session De
209. mmit to proceed Through the Smalltalk dependency mechanism any object can be registered as a dependent of a session In practice a session dependent is often a user visible application component such as a browser or a workspace When one application component asks to abort commit or log out the session asks all of its registered dependents to approve before it performs the operation If any registered dependent vetos the operation the operation is not performed and the method commitTransaction abortTransaction etc returns nil March 2006 GemStone Systems Inc 2 13 Session Dependents GemBuilder User Manual To make an object a dependent of a GbsSession send mySession addDependent myObj To remove an object from the list of dependents send the following message mySession removeDependent myObj So for example a browser object might include code similar to Example 2 2 in its initialization method Example 2 2 mySession mySession self session Add this browser to the sessions dependents list session dependents includes self ifFalse session addDependent self When a session receives a commit abort or logout request it sends an updateRequest message to each of its dependents with an argument describing the nature of the request Each registered object should be prepared to receive the updateRequest message with any one of the following aspect symbols as its argument qu
210. moveFromCommitOrAbortReleaseLocksSet aLockedObject aGbsSession removeAl1lFromCommitReleaseLocksSet aLockedCollection aGbsSession removeAl1FromCommitOrAbortReleaseLocksSet aLockedCollection The following GemStone Smalltalk statements remove all objects from the set of objects whose locks are to be released upon the next commit or abort These methods are executed using GS Do it System clearCommitReleaseLocksSet System clearCommitOrAbortReleaseLocksSet The statement aGbsSession commitAndReleaseLocks attempts to commit the current transaction and clears all locks for the session if the transaction was successfully committed March 2006 GemStone Systems Inc 7 15 Reduced conflict Classes GemBuilder User Manual 7 6 Reduced conflict Classes At times GemStone will perceive a conflict when two users are accessing the same object when what the users are doing actually presents no problem For example GemStone may perceive a write write conflict when two users are simultaneously trying to add an object to a Bag that they both have access to because this is seen as modifying the Bag GemStone provides some reduced conflict classes that can be used instead of their regular counterparts in applications that might otherwise experience too many unnecessary conflicts These classes are RcCounter RcIdentityBag RcKeyValueDictionary and RcQueue Use of these classes can improve performance by allowing a greater number of
211. n however you are implicitly giving GemStone permission to send your Gem session a signal requesting that you abort your current view so that GemStone can reclaim storage when necessary When this happens you must respond within the time period specified in the March 2006 GemStone Systems Inc 7 7 Transaction Modes GemBuilder User Manual STN_GEM_ABORT_TIMEOUT parameter in your configuration file If you do not GemStone either terminates the Gem or forces an abort depending on the value of the related configuration parameter STN_GEM_LOSTOT_TIMEOUT The Stone forces an abort by sending your session an abortErrLostOtRoot signal which means that your view of the repository was lost and any objects that your application had been holding may no longer be valid When your application receives abortErrLostOtRoot the application must log out of GemStone and log back in thus rereading all of its data in order to resynchronize its snapshot of the current state of the GemStone repository You can avoid abortErrLostOtRoot and control what happens when you receive a signal to abort with the signaledAbortAction aBlock message For example aGbsSession signaledAbortAction aGbsSession abortTransaction This causes your GemBuilder session to abort when it receives a signal to abort 7 4 Transaction Modes A GemBuilder session always initiates a transaction when it logs in After login the session can operate in either of two t
212. n Parameters Editor 2 8 settin Client Library 2 2 configuration parameters A 3 locks 7 13 Settings Browser VisualWorks 7 x A 9 SettingsBrowser VisualWorks 5i A 11 shared dictionaries 8 9 8 10 shared libraries required for runtime applications B 2 shared variables 3 12 sharing objects determining which 1 7 5 2 modifications and 7 10 signaledAbortAction GbsSession 7 8 signaling one Gem from another 7 18 Smalltalk GemStone features of 1 5 spawn hierarchy 10 8 special methods and breakpoints 4 7 selectors 3 17 special GBSM classes B 1 SpecialGemStoneObjects dictionary 5 31 stack examining in GemStone 4 10 getting trace without debugger 4 10 statistics gathering 11 2 step points 4 5 methods without 4 7 stepping 4 2 STN_GEM_ABORT_TIMEOUT GemStone configuration parameter 7 8 Stone name of 2 5 repository monitor 1 2 1 3 storage and reduced conflict classes 7 16 storing data in GemStone 6 20 stub 5 17 5 21 as argument to primitive method 5 20 controlling the stub level 11 8 converting 5 39 debugging A 8 defined 5 3 defunct 5 21 explicit control of 11 10 explicit creation 5 20 explicit stubbing 11 10 fault control and 11 8 faulting upon message receipt 5 18 instance variable access and 11 11 preventing transient 11 9 replicating 5 21 sending messages to 5 17 setting instance variables to nil A 5 stubDebugging configuration parameter A 2 Index 12 GemStone Systems Inc March 2006 GemBui
213. n beForwarderOnConnect GBSM addGlobalConnector conn When a GemBuilder session logs into the GemStone server BigDictionary becomes a valid forwarder to the current server BigDictionary But when no session is logged into the server sending a message to BigDictionary results in a defunct forwarder error GemBuilder s configuration parameter connectorNilling when true assigns each connector s variables to nil on logout This applies only to session based name class variable or class instance variable connectors that have a postconnect action of updateST or forwarder See Connectors on page 6 1 This usually prevents defunct stub and forwarder errors replacing them with nil doesNotUnderstand errors 5 4 Replicates Sometimes it s undesirable to dispatch a message to the other object space for execution sometimes local execution is desirable even necessary for example to reduce network traffic When local state and behavior is required share objects using replicates instead of forwarders Replicates are particularly useful for small objects objects having visual representations and objects that are accessed often or in computationally intensive ways Like a forwarder a replicate is a client Smalltalk object associated with a server object that the replicate represents Unlike a forwarder replicates also hold some state and implement some behavior Replicates synchronize their state with that of
214. n both modes If the clipboard item s name is already in use in the destination list a Confirmer will pop up to allow replacing the old item or to abort the paste operation Object Menu The Object Menu allows you add a new dictionary open an inspector on a dictionary entry and open a browser on a class that is contained ina dictionary Its menu items are Add Dict Inspect Dict and Browse Class Table 8 8 Object Menu in the Symbol List Browser Add Dict Prompts for name of a new item to be added to the Add Entry Dictionary or Entry list Inspect Dict Opens a GemStone inspector on the selected item Inspect Entry Browse Class If the selected entry is a class opens a GemStone class browser on that entry Performs the same operation in either Dictionary or Entry mode 8 22 GemStone Systems Inc March 2006 Security and Object Access GemStone Administration Tools Help Menu The Help menu contains one item Session Info which provides information about the session for the Symbol List Browser and about the current session User Account Management Tools The User Account Management tools are a set of three tools that allow the GemStone System Administrator to create new user accounts change account passwords and assign group membership This section describes the three User Account Management tools the GemStone User List the GemStone User Dialog and the Privileges Dialog Note
215. n classes You cannot modify any GemStone kernel class method that is any method that is defined for one of the predefined classes supplied with the GemStone system Public and Private Methods GemStone has both public and private methods Public GemStone methods are supported Private GemStone methods are those implemented to support the public protocol they are not supported and are subject to change Private GemStone methods are those whose selector is prefixed with an underscore _ They appear in the browsers along with the public methods and you can display the source for them CAUTION Private methods are subject to change at any time Do not depend on the presence or specific implementation of any private method when creating your own classes and methods Reserved and Optimized Selectors The following selectors are reserved for the sole use of the GemStone Smalltalk kernel classes Those selectors are ifTrue whileTrue timesRepeat ifFalse isKindof to do ifTrue ifFalse _isInteger to by do ifFalse ifTrue _isSmalliInteger untilFalse _isSymbol untilTrue _or _class whileFalse _and _trapOop Redefining a reserved selector has no effect the same primitive method is called and your redefinition is ignored In addition the following methods are optimized in the class SmallInteger 5s gt lt lt You can redefine the optimized methods above in your application classes but
216. n the Segment Tool Add Adds a new group In the Add Group dialog enter a name for the group and choose OK or Apply Remove Removes authorization for the selected group This does not delete the group from GemStone It only means that the current segment no longer stores access information for that group Users may still be able to access other objects because of their membership in the group but they will not have access to the objects assigned to this segment unless it has been provided by the segment s owner or world access Member Menu Use the Member menu to add users to and remove users from groups Table 8 4 Member Menu in the Segment Tool Add Adds a user to the group Enter any valid user name in the Add Member dialog and choose OK or Apply The user must already exist in the system You can use the User List to create new users Remove Removes the selected user from the group This does not delete the user from GemStone 8 16 GemStone Systems Inc March 2006 Security and Object Access GemStone Administration Tools Reports Menu Use the Reports menu to bring up a window displaying information about the segments users and groups in your view of the repository Use the window s Print button to print a report and use the Cancel button to close the window Table 8 5 Report Menu in the Segment Tool Group Report Produces a list of all groups in G
217. n tune your GemBuilder application to optimize performance and minimize maintenance overhead Profiling explains ways you can examine your program s execution Selecting the Locus of Control provides some rules of thumb for deciding when to have methods execute on the client and when to have them execute on the server Replication Tuning explains the replication mechanism and how you can control the level of replication to optimize performance Optimizing Space Management explains how you can reclaim space from unneeded replicates Using Primitives introduces the use of methods written in lower level languages such as C Changing the Initial Cache Size shows how to change the initial cache size Multiprocess Applications discusses nonblocking protocol and process safe transparency caches March 2006 GemStone Systems Inc 11 1 Profiling GemBuilder User Manual See Appendix A Configuring GemBuilder for GemBuilder configuration parameters that can used to tune performance For further information see the GemStone Programming Guide for a discussion on how to optimize GemStone Smalltalk code for faster performance That manual explains how to cluster objects for fast retrieval how to profile your code to determine where to optimize and discusses optimal cache sizes to improve performance 11 1 Profiling Before you can optimize the performance of your application you must find out where most of the execut
218. nd Managing Connectors GemBuilder User Manual 6 4 Making and Managing Connectors To make and manage connectors interactively see The Connector Browser on page 6 16 The next section describes making and managing connectors in code Making Connectors Programmatically GbsConnector is the abstract superclass for the connector class hierarchy These classes implement connection methods and define instance variables to refer to the associated GemStone and client objects Figure 6 4 shows the hierarchy Figure 6 4 Connector Class Hierarchy Object GbsConnector LS GbsNameConnector GbsFastConnector OS GbsClassConnector GbsClassVarConnector GbsClassinstVarConnector To create a connector programmatically 1 Create the connector 2 Set its postconnect action if other than the default 3 Add it to the global connector list or a connector list for session parameters Create the required GemStone session parameters and connectors in an initialization method Creation methods for session parameters are described in Defining Session Parameters on page 2 5 6 10 GemStone Systems Inc March 2006 Connectors Making and Managing Connectors Creating Connectors One simple creation method for a name connector requires only the names of the two objects to be connected GbsNameConnector stName stName gsName gsName You can create a class connector this way too GbsClassConnector stName st
219. nd uses slightly less CPU time This setting only affects non blocking RPC sessions and is ignored for linked sessions and for RPC sessions when blockingProtocolRpc is set to true This parameter is ignored in VisualWorks 5i on Windows which always uses polling pollForAsynchronousEvents This setting determines which method to use to detect asynchronous events from the GemStone server When true GBS uses a timed polling loop polling once every eventPollingFrequency milliseconds When false GBS waits for traffic on the socket that the gem uses for communication and also polls once every eventPollingFrequency milliseconds Under most circumstances the socket wait provides more timely notification of these events This parameter is ignored in VisualWorks 5i on Windows which always uses polling removelInvalidConnectors When true and confirm is false if a connector fails to resolve at login it is removed from the connector collections so that the issue does not arise again at next login When true and confirm is true you are prompted to remove invalid connectors during login When false invalid connectors are ignored March 2006 GemStone Systems Inc A 7 GemBuilder User Manual See The Connector Browser on page 6 16 rpcSocketWaitTimeoutMs When using the socket wait style of detecting when an RPC response is ready see the setting pollForRpcResponse it is possible for the socket event to get lost
220. nerally specify a postconnect action of none For similar reasons class connectors should not and in fact cannot specify that the client class is a forwarder the forwarder and clientForwarder postconnect action are unavailable for class connectors To determine the full list display the result of executing GbsForwarder nonForwarding If you change either a client or GemStone class definition during a session you must propagate the change yourself by disconnecting and reconnecting the connector The Connector Browser described starting on page 6 16 provides convenient buttons for the purpose NOTE Remember to restore a postconnect action of none after you complete the desired update 6 2 Connecting and Disconnecting At login connectors connect objects according to their specifications thereafter they are inactive Changes to instances that occur during the course of a session are replicated either because those instances are synchronized replicates that mark changes dirty or because one is a forwarder to the other Changes to class definitions or other unsynchronized changes must be propagated manually To do so use the Disconnect and Connect buttons in the Connector Browser to disconnect and reconnect the appropriate connector GemStone Systems Inc March 2006 Connectors Kinds of Connectors At logout to reduce the risk of defunct stub or forwarder errors GemBuilder sets connections to nil if at login they up
221. nerateServerClasses 2 GbsConfiguration default initialCacheSize traversalBufferSize 500000 initialDirtyPoolSize libraryName libraryName gcilw61 dll pollForAsynchronousEvents yourself pollForRpcResponse removelnvalidConnectors stubDebugging traversalBufferSize traversalCompression verbose Setting 4 Default a The VisualWorks 5i Settings Browser lists all parameters on the left Configuration parameters whose setting is not at the default are bold Selecting a parameter displays the description and allows you to modify the setting or restore the default Changes to parameter settings take place immediately March 2006 GemStone Systems Inc A 11 GemBuilder User Manual The VisualWorks 5i Settings Browser has the following buttons Table A 4 Buttons in the VW5i Settings Browser Default Resets the selected parameter to its default value OK Apply all changes and close the Settings Browser Cancel Close the Settings Browser without applying changes A 12 GemStone Systems Inc March 2006 Appendix Packaging Runtime Applications Use the following guidelines when packaging a client Smalltalk application that uses GemBuilder to access GemStone B 1 Prerequisites In addition to code required by your application the packaged image must contain the application or parcel GbsRuntime which contains the system code modified for GemBuilder In orde
222. nt It is almost always desirable to have GbsTools present during development but GbsTools can be omitted from most deployed applications March 2006 GemStone Systems Inc 1 9 Delivery and Deployment GemBuilder User Manual Public and Private Classes and Methods GemBuilder adds many classes and methods to your client Smalltalk image Some of these we consider public which means that they are designed to be referenced directly from your applications GemStone avoids changing public classes and methods from release to release Most GemBuilder classes and methods we consider private they are used to implement the internal workings of GemBuilder and are not designed to be referenced directly from applications Avoid using private classes and methods because they may have undocumented side effects and because they are subject to change from release to release A GemBuilder class is private if its name begins with the prefix Gbx A GemBuilder method can be marked private in any of several ways e Any method defined in a private class is private unless the class comment indicates otherwise e The selectors of private methods in base class extensions begin with the prefix gbx Some methods specify they are private in the method comment e Other methods are categorized as private in a method category marked private In general we encourage you to use in your applications only GemBuilder classes and methods that are do
223. nt Smalltalk compiler and decompiler if they ve been removed from a deployed runtime environment blocks cannot be replicated Two workarounds are possible 1 Leave the compiler and decompiler in the image For example the VisualWorks Image Maker tool offers a Remove Compiler option which you can deselect to leave the compiler and decompiler in the image 2 Do not use block replication Usually this requires implementing a cover method for the block in a GemStone method and sending that message instead For instance aForwarder select name name Fred is instead coded aForwarder selectNameEquals Fred 5 32 GemStone Systems Inc March 2006 Sharing Objects Replicates and in GemStone selectNameEquals is implemented as selectNameEquals aName self select name name aName When the block is encoded entirely in GemStone in this way you can further optimize its operation by taking advantage of indexes and use an optimized selection block as described in the GemStone Programming Guide Temporary Variable Reference Restrictions A block is replicated in the form of its source code without its surrounding context Therefore values drawn from outside the block s own scope cannot be relied upon to exist in both the client Smalltalk and in GemStone Replication is not supported for blocks that reference instance variables class variables method arguments or temporary varia
224. nues a transaction passes a transaction boundary which refreshes your session s private view of the repository If the server object has been changed by some other concurrent session and that change was committed the object s new state will be visible when your session refreshes its view In both of these cases the replicate s state is now out of date and cannot be used until updated by faulting Depending on the replicate s faultPolicy see page 5 20 the new state will either be faulted immediately or the replicate becomes a stub and will be faulted the next time it receives a message GemBuilder flushes dirty client objects to the GemStone server at transaction boundaries immediately before any GemStone Smalltalk execution or before faulting a stub Flushing is not the same as committing When GemBuilder flushes an object the change becomes part of the session s private view of the GemStone repository but it doesn t become part of the shared repository until your session commits only then are your changes accessible to other users For GemBuilder to flush a changed object to the server that object must be marked dirty that is GemBuilder must be made aware that the object has changed Objects can be marked dirty automatically depending on the version of client Smalltalk or you can explicitly mark objects dirty Marking Modified Objects Dirty Automatically in VW 7 x By default GemBuilder uses features of the Visual
225. o keep objects synchronized presents various mechanisms to minimize performance costs presents further details Precedence of Replication Mechanisms discusses the various ways replication mechanisms interact and describes March 2006 GemStone Systems Inc 5 1 Which Objects to Share GemBuilder User Manual how to determine whether an application object becomes a forwarder stub or replicate Converting Between Forms lists protocol for converting from and to delegates forwarders stubs replicates and unshared client objects 5 1 Which Objects to Share Working with your client Smalltalk you had one execution engine the virtual machine acting on one object space your image Now that you ve installed GemBuilder you have two execution engines and two object spaces one of which is a full fledged object repository for multiuser concurrent access with transaction control security protections backups and logging What s the best way to make use of these new resources Objects represent both state and behavior Therefore you have two basic decisions e Which state should reside on the client which on the server and which in both object spaces e Which behavior should reside on the client which on the server and which in both object spaces Ultimately the answer is dictated by the unique logic of your specific problem and solution but these common patterns emerge Client presents user interface on
226. of the GemStone Programming Guide for GemStone Smalltalk syntax with the exceptions that the code O cannot take any arguments O must not refer to the variables self or super O must not refer to any instance variable of any class Example 5 9 shows how to use evaluate to execute code March 2006 GemStone Systems Inc 5 37 Evaluating Smalltalk Code on the GemStone server GemBuilder User Manual Example 5 9 resultReplicate GBSM currentSession evaluate result result Array new 3 result at 1 put Pear at 2 put unripe at 3 put 42 result A You can avoid some of these restrictions by passing in a context object using aGbsSession evaluate aString context aServerObject or aGbsSession fwevaluate aString context aServerObject The context argument aServerObject can be any replicate of or forwarder to a GemStone server object If the code in aString refers to the variables self or super these will be bound to the context object The code in aString can also refer to any instance variables of the context object Example 5 10 aGbsSession evaluate self at 2 put ripe context resultReplicate The advantage of the evaluate family of messages is that they allow you to execute arbitrary ad hoc code on the server without previously defining a method However this isn t always the best way to execute server code The evaluate messages invoke the Ge
227. og 2 Inthe Segment Tool choose Reports gt Segment Report The resulting list contains all segments 3 To view the members of each group choose Reports gt Group Report To view the groups to which each user belongs choose Reports gt User Report Changing Segment Authorization Assuming that you either have SegmentProtection privileges or are the segment s owner you can use the Segment Tool to change the authorization of a segment The top half of the Segment Tool shows the owner the owner s access and world access for each segment in the repository To change owner or world access select the existing permission you want to change Then enter a new permission read write or none The new authorization will take effect when you commit the current transaction CAUTION Be careful to check whether a user is logged in before you remove write authorization A user will be unable to commit changes if write authorization is removed from the current segment and if it is the user s default segment the user s session will be terminated and the user will be unable to log in again Controlling Group Access to a Segment If you are authorized to set up or change group access to a segment you can add or remove groups to that segment s authorization list e Make sure the segment is selected in the top half of the tool e To add a group to the authorization list for the selected segment choose Add from t
228. oice Navigate to a specific class by name The search string is case sensitive and can include wild cards 3 6 GemStone Systems Inc March 2006 Using the GemStone Programming Tools Browsing Code Class Pane The GemStone specific menu commands available in the GemStone Browser s Class Pane are described in Table 3 3 A later section discusses the procedure required to add the definition of a new GemStone class to the currently selected symbol dictionary Table 3 3 Class Menu in GemStone Browser file out as file out methods as browse class browse hierarchy browse versions browse references hierarchy definition comment move to Prompts you for a file name under which to save all the methods of the selected class so that you can file them into a client class without changing the client class s structure Open a class browser on the selected class Open a hierarchy browser on the selected class Open a class version browser on the selected class Open a method list on all references to the current version of the class or all versions of the class Display the class hierarchy in the text pane Display the class definition in the text pane the default Display the class comment in the text pane Prompt for another SymbolDictionary to which to move the selected class March 2006 GemStone Systems Inc 3 7 Browsing Code GemBuilder User Manual Table 3 3 Clas
229. ol involve privileged methods If your account does not have the needed privileges ask your system administrator to set up your segments for you To open a Segment Tool select Admin gt Segments from the GemStone menu or through the User Dialog s Show Segments button Figure 8 2 shows a Segment Tool Figure 8 2 The Segment Tool Segment Tool on Session 1 linked for DataCurator on gemserverb1 E Oj x File Segment Group Member Reports Help Curren Defaul Segment Name Owner Name Owner Access World Access Current Default DataCuratorSegme DataCurator write read Segments gt GsTimeZoneSegm SystemUser write write PublishedSegment SystemUser write none SecurityDataSegmd SystemUser write none SystemSegment SystemUser write read Note Changes take place immediately Group Name Group Access Member List Members of Groups March 2006 GemStone Systems Inc 8 11 GemStone Administration Tools GemBuilder User Manual The Segment Tool is divided into two main sections one displays segments the other displays groups and their members Segment Definition Area The segment definition area at the top of the dialog displays the segments in the SystemRepository to which the current user has read authorization You will notice that some segments are named and some are unnamed Named segments are segments that are referenced in a dictionary or s
230. on commits a change to b and b s fault policy is lazy b becomes a stub If b s fault policy is immediate b is updated The default fault policy is lazy to minimize network traffic For more information see the description of defaultFaultPolicy in the Settings Browser For examples browse implementors of faultPolicy in the GemBuilder image Overriding Defaults Because linked sessions can access the gem with lower latency GemBuilder ships with faultLevelLnk set to 2 and faultLevelRpc set to 4 In this way linked sessions replicate less at login faulting in objects as they are needed e You can override these defaults for specific instance variables of specific replicates e You can also stub or replicate certain objects explicitly To specify fault levels for all instance variables implement a class method replicationSpec for the client class Replication specifications are versatile mechanisms described starting on page 5 21 To cause a replicate to become a stub send it the message stubYourself This can be useful for controlling the amount of memory required by the client Smalltalk image Explicit control of stubs is discussed in Optimizing Space Management on page 11 9 Sometimes stubbing is not desirable either for performance reasons or for correctness For example primitives cannot accept stubs as arguments if the 5 20 GemStone Systems Inc March 2006 Sharing Objects Replicates primitive acc
231. onary for the server object Specify the postconnect action To create a forwarder 1 2 Create a connector as described above Select forwarder as the desired postconnect action To change the postconnect action 1 2 3 Disconnect the objects by clicking on the Disconnected button Change the postconnect action as required Reconnect the objects by clicking on the Connected button March 2006 GemStone Systems Inc 6 19 Making and Managing Connectors GemBuilder User Manual If your application initially stores its data in the client and you intend to store the data on the GemStone server but have not done so yet 1 2 3 Create a connector or connectors for the root object s in the data set Select updateGS as the postconnect action for these connectors Log into the GemStone server so that GemBuilder can create the GemStone server replicates for the client Smalltalk data Inspect the GemStone server objects to be sure they have the intended values Commit the transaction and log out Select the connectors and change their postconnect actions to updateST so that future sessions will begin by using the stored GemStone server data 6 20 GemStone Systems Inc March 2006 Chapter Managing Transactions The GemStone object server s fundamental mechanism for maintaining the integrity of shared objects in a multiuser environment is the transaction This chapter describes
232. one Stub Stub Faulting in Response to a Message When object e a stub receives a message it faults in a replicate of its counterpart GemStone server object A stub faults in a replicate in response to a message Therefore direct references to instance variables can cause problems Direct access is not a message send the stub will not fault in its replicate because it receives no message neither can it supply the requested value To avoid this problem use accessor methods to get or set instance variables The following sequence demonstrates the problem The object starts as a replicate in client Smalltalk myVar abc 5 18 GemStone Systems Inc March 2006 Sharing Objects Replicates Next it s stubbed There are several ways it could become a stub for this example we ll assume that it became a stub by locking locking an object stubs it self mySession writeLock self The object now a stub has no knowledge of the replicate s instance variables Therefore executing the code below later in the same method causes an error myVar bcd Using an accessor method on the other hand causes the stub to be faulted in and yields the correct result self myVar bcd e is now a replicate as shown in Figure 5 2 The new replicate responds to the message Figure 5 2 A Stub Responds to a Message Client Smalltalk GemStone Again
233. onment variable are not reflected in the behavior of an already running utility When a client utility submits a request to a NetLDI the utility uses its own defaults and those gleaned from its environment to build the NRS After the NRS is submitted to it the NetLDI then applies additional defaults if needed Values submitted by the client utility take precedence over those provided by the NetLDI C 3 Notation Terminal symbols are printed in boldface They appear in a network resource string as written server Nonterminal symbols are printed in italics They are defined in terms of terminal symbols and other nonterminal symbols username nrs identifier Items enclosed in square brackets are optional When they appear they can appear only one time address modifier protocol node Items enclosed in curly braces are also optional When they appear they can appear more than once nrs header address modifier keyword modifier March 2006 GemStone Systems Inc C 3 Syntax GemBuilder User Manual Parentheses and vertical bars denote multiple options Any single item on the list can be chosen protocol tcp decnet serial default C 4 Syntax nrs nrs header nrs body where nrs header address modifier keyword modifier resource modifier All modifiers are optional and defaults apply if a modifier is omitted The value of an environment variable can be placed
234. onnected when required and object retrieval may slow A connector is managed by adding it to the appropriate list of connectors If you want a connector in effect whenever any session logs in put it in the global connectors collection GBSM addGlobalConnector aConnector A new global connector first takes effect the next time any session logs in Each session parameters object maintains its own list of session connectors If you want a connector in effect whenever a session logs in using specific parameters add a connector to the session parameters object ThisApplicationParameters addConnector aConnector A new session connector first takes effect the next time that session logs in To initialize a system with two roots the global BigDictionary and a class variable in MyClass called MyClassVar your application might execute code such as that shown in Example 6 1 Example 6 1 GBSM addGlobalConnector GbsNameConnector stName MyGlobal gsName MyGlobal addGlobalConnector GbsClassVarConnector stName MyClass gsName MyClass cvarName MyClassVar Initialization code such as that in Example 6 1 needs to execute only once From then on every time you log into GemStone MyGlobal and MyClassVar and all the objects they reference connect after that replication and updating occur as specified 6 12 GemStone Systems Inc March 2006 Connectors Making an
235. onnectors 6 5 locks 7 14 unresolved connectors 6 18 A 7 replicate 5 9 5 37 as argument to primitive method 5 20 converting 5 39 customized faulting of 5 22 defined 5 3 fault control and 11 8 flushing dirty 5 11 11 7 locking and stubbing 5 19 preventing stubbing 5 21 Index 10 GemStone Systems Inc March 2006 GemBuilder User Manual update direction 5 9 when to use 5 9 replicating blocks avoiding 5 35 client Smalltalk blocks 5 31 A 4 limits of 5 31 5 36 minimizing costs of 5 14 precedence of various mechanisms 5 36 suppressing instance variables 5 15 replication specification 5 21 5 27 class versions and 5 23 declaring forwarder in 5 7 inheritance and 5 22 managing dependencies between objects with 5 25 precedence 5 26 root object for 5 26 specifying fault levels in 5 20 switching among several 5 24 replicationSpecSet 5 24 reposito modifying 5 10 7 10 overview 1 2 Repository class 8 4 reserved selectors 3 17 return value from forwarder 5 8 root objects 6 2 6 4 in replication specifications 5 26 RPC Gems using blocking protocol for A 3 RPC session 2 3 rpcSocketWaitTimeoutMs configuration parameter A 2 A 8 RT_ERR_SIGNAL_ABORT signal 7 7 runtime applications B 1 S saving class and method definitions 3 18 coordinating 10 6 matching and instance variable mapping 5 5 modification 10 2 class versions and 10 6 scope of connectors 6 4 security 1 8 login
236. ons where a client Smalltalk user interrupt sends a soft break a hard break will be sent after the server has not responded to three soft breaks 9 6 GemStone Systems Inc March 2006 Chapter 10 Schema Modification and Coordination No matter how elegantly your schema was designed sooner or later changes in your application requirements or even changes in the world around your application will probably make it necessary to make changes to classes that are already instantiated and in use When this happens you will want the process of propagating your changes to be smooth and to impact your work as little as possible This chapter discusses the mechanisms GemStone and GemBuilder provide to help you accomplish this Schema Modification explains how GemStone supports schema modification by maintaining versions of classes in class history objects It shows you how to migrate some or all instances from one version of a class to another while retaining the data that these instances hold Schema Coordination explains how to synchronize schema modifications between GemStone and the client Smalltalk The Class Version Browser describes a specialized Class Browser that can be used for examining a class March 2006 GemStone Systems Inc 10 1 Schema Modification GemBuilder User Manual history inspecting instances migrating instances deleting versions and moving versions to another class history 10
237. ontrol faulting initialization and postprocessing preFault and postFault Implement preFaul1t to initialize a newly created object prior to faulting its named and indexable values For example OrderedCollection gt gt preFault Initialize lt firstIndex gt and lt lastIndex gt prior to adding elements self setIndices 5 28 GemStone Systems Inc March 2006 Sharing Objects Replicates The method indexableValueAt put for OrderedCollection has an implementation similar to Set to add the indexable objects As another example a specialized type of SortedCollection could use preFault to assign the sortBlock so that additions to the collection would be sorted properly during faulting Implement postFault to do any necessary postprocessing For example if the methods used to add to an OrderedCollection also marked the object dirty the postprocessing could remove dirty marking by definition faulting never results in a dirty object assuming that the valid state is the state on the OrderedCollection gt gt postFault Additions to the OrderedCollection are due to the faulting mechanisms and should not result in a dirty object self markNotDirty Modifying Instance Variables During Flushing To provide an arbitrary mapping of objects from the client to the server you can implement two class methods called namedValues and indexableValues namedValues Implement this to return a copy of the ob
238. oordinating Faulting If two processes send a message to a stub at roughly the same time one of the processes can receive an incomplete view of the contents of the object This results in doesNotUnderstand errors which cannot be explained by looking at them under a debugger because by the time it is visible in the debugger the object has been completely initialized Unstubbing conflicts can be avoided by 11 14 GemStone Systems Inc March 2006 Performance Tuning Multiprocess Applications encapsulating potential unstubbing operations within the protection of a GbsSession gt gt critical block Using the VisualWorks Application Model As mentioned above an application that otherwise restricts itself to one process per GemStone session can occasionally find itself running multiple processes against a single session through the asynchronous operation of signals and notifiers One way to coordinate the activities of signal and notifier processes is to remap asynchronous GemStone events into synchronous window events as though they were received through the user interface Implementing this strategy requires two steps The first is to use some or all of the following methods to redirect GemStone signals and notifiers to the application model GbsSession gt gt sendGemSignalEventsTo anApplicationModel gt gt sendNotificationEventsTo anApplicationModel gt gt sendSignaledAbortEventsTo anApplicationModel For example you
239. orts schema modification by maintaining versions of classes in class histories It describes the Class Version Browser and explains how to use it It also explains how to synchronize schema modifications between the client and GemStone Chapter 11 Performance Tuning discusses ways that you can tune your application to optimize performance and minimize maintenance overhead It describes the configuration parameters available for tuning a GemBuilder application and it explains how to configure GemBuilder for Smalltalk to optimize your application s performance Appendix A Configuring GemBuilder describes the GemBuilder for Smalltalk configuration options and how to set and use them Appendix B Packaging Runtime Applications provides brief instructions for packaging runtime applications Appendix C Network Resource String Syntax describes the syntax for network resource strings a means for uniquely identifying a GemStone file or process by specifying its location on the network its type and authorization information Appendix D Client Smalltalk and GemStone Smalltalk outlines the few general and syntactical differences between the client Smalltalk and GemStone Smalltalk dialects Other Useful Documents You will find it useful to look at documents that describe other components of the GemStone data management system e The GemStone Programming Guide describes GemStone Smalltalk and discusses managing common operations e
240. otection O File Control C Garbage Collection The privileges and the methods that are associated with them are shown in Table 8 13 Table 8 13 Privileges Type of Privilege Privileged Methods In Class System Control resumeLogins shutDown stopOtherSessions stopSession suspendLogins System Statistics stoneStatistics System Session Access concurrencyMode currentSessionNames currentSessions descriptionOfSession stopOtherSessions userProfileForSession System User Password oldPassword newPassword UserProfile 8 28 GemStone Systems Inc March 2006 Security and Object Access GemStone Administration Tools Table 8 13 Privileges Type of Privilege Privileged Methods In Class Default Segment defaultSegment UserProfile Other Password password UserProfile Segment Creation newInRepository Segment Segment Protection group authorization ownerAuthorization worldAuthorization Segment File Control abortRestore addTransactionLog replicate size commitRestore continueFullBackupTo MBytes createExtent createExtent withMaxSize createReplicateo0f named disposeReplicate fullBackupTo fullBackupTo MBytes restoreFromBackup restoreFromBackups restoreFromCurrentLogs restoreFromLog shrinkExtents startNewLog Repository Garbage Collection
241. ove 10 9 moving data into GemStone 6 20 multiprocess applications 11 12 N name connector 6 7 name of superclass specifying 3 12 namedValueAt 5 30 namedValueAt put 5 28 namedValues 5 29 Index 8 GemStone Systems Inc March 2006 GemBuilder User Manual namedValues indexableValues 5 27 namedValuesBuf fer 5 27 5 28 network node 2 6 of objects connecting 6 2 resource string syntax D 1 notification Gem to Gem 7 18 NRS network resource string syntax D 1 O object business 1 8 domain 1 8 repository overview 1 2 object level invariance 3 11 optimization and multiprocess applications 11 12 and traversal buffer size 11 9 by explicit stubbing 11 10 by using forwarders 11 11 changing the initial cache size 11 12 choosing execution platform 5 2 choosing the execution platform 11 7 controlling replication level and 5 17 controlling the locus of execution 11 6 controlling the replication level 11 8 cost of data management 11 7 explicit stubbing and 5 20 minimizing replication cost 5 14 5 27 preventing transient stubs 11 9 reduced conflict classes and 7 16 statistics gathering for 11 2 using forwarders 5 6 11 11 using GemStone Smalltalk for searching and sorting large objects 11 8 using GemStone user actions and client Smalltalk primitives 11 11 order in which connectors are connected 6 8 P packaging runtime applications B 1 parameter in message to forwarder 5
242. owerful single things you can do to improve performance is to move some of the behavior from the client to the GemStone server and let the GemStone Smalltalk execution engine do the work This approach reduces network traffic which is a prime cause of slow performance Which methods might best be executed on the GemStone server GemStone already contains behavior for many of the common Smalltalk kernel classes and as mentioned earlier the syntax and class hierarchy of GemStone s Smalltalk language are so similar to those of other Smalltalks that the porting effort is likely to be relatively simple Performance issues in general are discussed in Chapter 11 Moving execution to the GemStone server is discussed in the section entitled Locus of Execution on page 11 6 Finally you can configure the GemStone object server for maximum performance given the details of your application and environment GemStone server configuration parameters are discussed in detail in the GemStone System Administration Guide in addition the GemStone Programming Guide gives a variety of tips in the chapter entitled Tuning Performance 1 4 Delivery and Deployment GemBuilder is provided in the form of parcels or ENVY applications named GbsRuntime GbsTools and CstMessengerSupport GbsRuntime and CstMessengerSupport are required for all uses of GemBuilder GbsTools contains development and administration tools that are normally used only during developme
243. oyee giving her a raise and then moving on to another unrelated operation Although a brute force search may be faster in your client Smalltalk the cost of moving the data to the client may exceed the savings The search should probably be done in GemStone However if additional operations are going to be done on the employee set the cost of moving data is amortized and as the number of operations increases becomes less than the potential savings March 2006 GemStone Systems Inc 11 7 Replication Tuning GemBuilder User Manual GemStone Optimization Some optimizations are possible only using GemStone server execution In particular repository searching and sorting can be done much more quickly on the GemStone server than in your client Smalltalk as data sets become large If you will be doing frequent searches of data sets such as the employee set in the previous example using an index on the server Smalltalk set will speed execution The GemStone Programming Guide provides a complete discussion of indexes and optimized queries 11 3 Replication Tuning The faulting of GemStone server objects into the client Smalltalk is described in Chapter 5 As described there a GemStone server object has a replicate in the client Smalltalk created for itself and recursively for objects it contains to a certain level at which point stubs instead of replicates are created Faulting objects to the proper number of levels can
244. oyee name extraArg with tempName Restriction on References to self or super References to self and super are also context sensitive and therefore disallowed e A replicated block cannot contain references to self or super For example the following code cannot be forwarded to GemStone because the parameter block contains a reference to self myDict at key ifAbsent self References to self or super in forwarded code must occur outside the scope of the replicated block where you can be sure of the context within which they occur For example you can rewrite the above code to return a result code which can then be evaluated in the calling context outside the scope of the replicated block result myDict at key ifAbsent absent result absent ifTrue self Explicit Return Restriction Because a block is replicated without its surrounding context a return statement has no surrounding context to which to return Therefore e A replicated block cannot contain an explicit return For example result myDict at key ifAbsent nil is disallowed The statement can be recoded to perform its return within the calling context myDict at key ifAbsent absent absent ifTrue nil resul resul t t 5 34 GemStone Systems Inc March 2006 Sharing Objects Replicates Replicating GemStone Blocks in Client Smalltalk Also supported though less commonly used is
245. p 1 Open a new client image as shipped from your client Smalltalk vendor Step 2 Ensure that you have satisfied the prerequisites given above Step 3 Load your application code Step 4 Follow the packaging instructions given by your Smalltalk vendor B 2 GemStone Systems Inc March 2006 Appendix Network Resource String Syntax This appendix describes the syntax for network resource strings A network resource string NRS provides a means for uniquely identifying a GemStone file or process by specifying its location on the network its type and authorization information GemStone utilities use network resource strings to request services from a NetLDI C 1 Overview One common application of NRS strings is the specification of login parameters for a remote process RPC GemStone application An RPC login typically requires you to specify a GemStone repository monitor and a Gem service on a remote server using NRS strings that include the remote server s hostname For example to log in from Topaz to a Stone process called gemserver61 running on node handel you would specify two NRS strings topaz gt set gemstone handel gemserver61 topaz gt set gemnetid handel gemnetobject March 2006 GemStone Systems Inc C 1 Defaults GemBuilder User Manual Many GemStone processes use network resource strings so the strings show up in places where command arguments are recorded such as t
246. pendent 1 Commit Request GemStone Repository 5 Update 2 Update Request 3 Request Approved Class Browser _ Dependent of Session March 2006 GemStone Systems Inc 2 17 Session Dependents GemBuilder User Manual 2 18 GemStone Systems Inc March 2006 Chapter Using the GemStone Programming Tools After you install GemBuilder many menus in your Smalltalk image contain additional commands for executing GemStone Smalltalk code and accessing GemBuilder programming tools These tools are in many ways similar to those of the client Smalltalk but with important differences this chapter describes those differences GemStone Menu introduces the tools and options available from the GemStone menu Browsing Code describes the GemStone Classes Browser and other code browsers System Workspace describes the System Workspace Coding explains how to use the GemBuilder tools to create classes and methods in GemStone Smalltalk for execution and storage on the server March 2006 GemStone Systems Inc 3 1 GemStone Menu GemBuilder User Manual 3 1 GemStone Menu The GemStone menu accessible from various tools gives you access to the GemStone Smalltalk compiler and the GemBuilder programming tools Many of these functions are also available from pop up menus in the browsers and tools As shown in Table 3 1 the GemStone menu provides commands for executing
247. ple e aForwarder at 1 returns a replicate of the object at index 1 e aForwarder fwat 1 returns a forwarder to the object at index 1 Defunct Forwarders A forwarder contains no state or behavior in one object space relying on the existence of a valid instance in the other When a session logs out of the server communication between the two spaces is interrupted Forwarders that relied on objects in that session can no longer function properly If they receive a message GemBuilder raises an error complaining of either an invalid session identifier or a defunct forwarder You cannot proceed from either of these errors an operation that encounters one must restart presumably after determining the cause and resolving the problem GemBuilder cannot safely assume that a given server object will retain the same object identifier OOP from one session to the next Therefore you can t fix a defunct forwarder error simply by logging back in If a connector has been defined for that object or for its root then logging back in will indeed fix the error because logging back in will connect the variables But in that case it s the connector not the forwarder that repairs damaged communications Consider the following forwarder for the global BigDictionary 5 8 GemStone Systems Inc March 2006 Sharing Objects Replicates Example 5 1 conn GbsNameConnector stName BigDictionary gsName BigDictionary con
248. ple 7 2 First set up notifying objects and notification action notifier BSM currentSession abortTransaction clearNotifySet otifier Array new 1 BSM currentSession at Notifier put notifier BSM currentSession commitTransaction BSM currentSession addToNotifySet notifier BSM currentSession notificationAction objs Transcript cr show Notification received G n G G G G Now from any session logged into the same stone with visibility to the object notifier to initiate notification GBSM currentSession abortTransaction evaluate Notifier at 1 put Object new commitTransaction Gem to Gem Notification Sessions can send general purpose signals to other GemStone sessions allowing the transmission of the sender s session a numerical signal value and an associated message One Gem can handle a signal from another using the method GbsSession gt gt sessionSignalAction aBlock where aBlock is a one argument block that will be passed a forwarder to the instance of GsInterSessionSignal that was received From the GsInterSessionSignal instance you can extract the session signal value and string One GemStone session sends a signal to another with aGbsSession sendSignal aSignal to aSessionId withMessage aString 7 18 GemStone Systems Inc March 2006 Managing Transactions Changed Object Notification For example Example 7 3 First set
249. pository Figure 7 1 shows a client image and its repository along with a common sequence of operations 1 faulting in an object from the shared repository to Smalltalk 2 flushing an object to the private GemStone view and 3 committing the object s changes to the shared repository Figure 7 1 GemBuilder Application Workspace 2 Flush 3 Commit Client Smalltalk Private GemStone Image GemStone View Repository March 2006 GemStone Systems Inc 7 3 Operating Inside a Transaction GemBuilder User Manual The private GemStone view starts each transaction as a snapshot of the current state of the repository As the application creates and modifies shared objects GemBuilder updates the private GemStone view to reflect the application s changes When your application commits a transaction the repository is updated with the changes held in your application s private GemStone view For efficiency GemBuilder does not replicate the entire contents of the repository It contains only those objects that have been replicated from the repository or created by your application for sharing with the object server Objects are replicated only when modified This minimizes the amount of data that moves across the boundary from the repository to the Smalltalk application Committing a Transaction When an application submits a transaction to the object server for inclusion in the shared repository it is sa
250. ptions in the Control Panel o ee 6 18 Postconnect Action Options in the Connector Browser 6 18 GbsSession Methods for Running Outside of a Transaction 7 7 File Menu in the Segment Tool o ooo 8 14 Segment Menu in the Segment Tool o o o o ooo 8 15 Group Menu in the Segment Tool 8 16 March 2006 GemStone Systems Inc xxi GemBuilder User Manual Table 8 4 Member Menu in the Segment Tool o o o 8 16 Table 8 5 Report Menu in the Segment Tool o o o o o ooo o 8 17 Table 8 6 File Menu in the Symbol List Browser 8 21 Table 8 7 Edit Menu in the Symbol List Browser o 8 22 Table 8 8 Object Menu in the Symbol List Browser 8 22 Table 8 9 GemStone User List File Menu o o 8 24 Table 8 10 GemStone User List o o e 8 25 Table 8 11 Buttons in the GemStone User Dialog 8 26 Table 8 12 GemStone User Dialog FileMenu 8 27 Table 8 13 Privileges 2 ee 8 28 Table 10 1 Class Menu in Class Version Browser o o 10 8 Table 11 1 Session Manager Main Statistics o o 11 3 Table 11 2 Session Main Statistics 2 o e ee 11 3 Table A 1 Configuration Parameters forGemBuilder A 1 Table A 2 VW7 Settings Browser Categorization A 9 Table A 3 Button
251. r modification of sensitive code and data These mechanisms are listed below and you can choose to use any or all of them Requiring Login Authorization GemStone s first line of protection is to control login authorization When someone tries to log in to GemStone GemStone requires a user name and password If the username and password match the user name and password of someone authorized to use the system GemStone allows interaction to proceed if not the connection is severed The GemStone system administrator controls login authorization by establishing user names and passwords when he or she creates UserProfiles Controlling Visibility of Objects You can also control access by hiding certain objects from users Because it is difficult if not impossible for users to refer to objects that are not defined somewhere in their symbol lists simply omitting off limits objects from a user s symbol list provides a certain amount of security It is possible however for users to find ways to circumvent this because it s difficult to ensure that all indirect paths to an object are eliminated Protecting Methods Another choice is to implement procedural protection If your program accesses its objects only through methods you can control the use of those objects by including user identity checks in the accessing methods 8 2 GemStone Systems Inc March 2006 Security and Object Access Object Level Security Using Gem
252. r to ensure that your image initializes correctly your application must specify GbsRuntime as a prerequisite Do not include the application or parcel GbsTools These are subclasses of classes that will be deleted during the packaging process Names Ensure that your image is packaged to include class pool dictionaries and instance variable names and does not remove them March 2006 GemStone Systems Inc B 1 Packaging GemBuilder User Manual Replicating Blocks To ensure that your application is able to replicate Smalltalk blocks in the same manner as it did in the development environment we recommend that you include the compiler Defunct Stubs and Forwarders Defunct stubs and forwarders cause problems during packaging To avoid these problems start with new client image as shipped from your client Smalltalk vendor Shared Libraries A deployed runtime application that uses GemBuilder needs to contain all the server specific shared libraries as well as the as the error file english err or englisxx err where xxis the release number The Installation Guide for the GemStone server product and version you are using will provide the specific names of the library files If you are logging in only remote sessions set the GemBuilder configuration parameter libraryName to the RPC version of the GemStone client libraries Again see the appropriate installation guide for the specific library names B 2 Packaging Ste
253. rademarks of their respective owners Trademark specifications are subject to change without notice All terms mentioned in this documentation that are known to be trademarks or service marks have been appropriately capitalized to the best of our knowledge however GemStone cannot attest to the accuracy of all trademark information Use of a term in this documentation should not be regarded as affecting the validity of any trademark or service mark GemStone Systems Inc 1260 NW Waterhouse Avenue Suite 200 Beaverton OR 97006 GemStone Systems Inc March 2006 Preface About This Manual This manual describes GemBuilder for Smalltalk an environment for developing Gemstone applications using VisualWorks Smalltalk GemBuilder for Smalltalk consists of two parts a programming interface between your client Smalltalk application code and the GemStone object repository and a GemStone programming environment The programming interface provides facilities for managing the relationship between objects on the GemStone server and in client Smalltalk allowing objects to be available on the client and updated on the shared GemStone server The GemBuilder programming environment provides a set of integrated tools for programming in GemStone s version of Smalltalk GemBuilder supports each of the GemStone server products GemStone S GemStone S 64 Bit and GemStone S 2G There are minor differences between the features availab
254. ransaction modes automatic or manual Automatic Transaction Mode In automatic transaction mode committing or aborting a transaction automatically starts a new transaction This is GemBuilder s default transaction mode in this mode the session operates within a transaction the entire time it is logged into GemStone However being in a transaction incurs certain costs related to maintaining a consistent view of the repository at all times for all sessions Objects that the repository contained when you started the transaction are preserved in your view even if you are not using them and other users actions have rendered them meaningless or obsolete Depending upon the characteristics of your particular installation such as the number of users the frequency of transactions and the extent of object sharing this burden can be trivial or significant If it is significant at your site you may want to reduce overhead by using sessions that run outside transactions To run outside a transaction a session must switch to manual transaction mode 7 8 GemStone Systems Inc March 2006 Managing Transactions Transaction Modes Manual Transaction Mode In manual transaction mode the session remains outside a transaction until you begin a transaction When you change the transaction mode from automatic its initial setting to manual the current transaction is aborted and the session is left outside a transaction In manual transa
255. re set in the superclass that defined them if any Instances can be invariant A class definition can specify that all instances are invariant meaning they can be modified only during the transaction in which it is created After the transaction is committed you can no longer modify its instance variables nor the size or class of the object Specify invariance for a class by providing the argument true to the instancesInvariant keyword in the class definition template Class level invariance is useful for supporting literals in methods and in other limited situations but it is generally more cumbersome than object level invariance Any object can be made invariant by sending it the message immediateInvariant This mechanism protects objects from being modified and can be useful for maintaining the integrity of your repository After immediateInvariant is sent to an object you can no longer modify its instance variables nor the size or class of the object The effect of the immediateInvariant message is not reversible The message isInvariant returns true if the receiver is invariant false otherwise March 2006 GemStone Systems Inc 3 11 Coding GemBuilder User Manual Defining a New Class To define a new GemStone class Step 1 Open a GemStone Browser if one is not already open Step 2 In the Symbol List pane select the dictionary in which you wish to refer to the new class Make sure no class is selecte
256. redefinitions in the class SmallInteger are ignored March 2006 GemStone Systems Inc 3 17 Coding GemBuilder User Manual Saving Class and Method Definitions in Files It s often useful to store the GemStone Smalltalk source code in text files Such files make it easy to e transport your code to other GemStone systems e perform global edits and recompilations e produce paper copies of your work and e recover code that would otherwise be lost if you are unable to commit To save GemStone code in a file use any of the GemStone browser s File Out menu items To read and compile a saved file use any of the Gs File in or GS File it in menu items Saved GemStone files are written as sequences of Topaz commands Example 3 2 shows a class definition in Topaz format Example 3 2 From GEMSTONE 6 1 3 Thu Jun 10 16 32 27 US Pacific 2004 IMAGE GemStone v6 1 kernel classes filein completed at 11 06 2004 13 09 32 GemStone v6 1 kernel classes filein of stripped sources completed at 11 06 2004 14 25 00 On February 10 2005 1 44 20 pm I doit Object subclass Address instVarNames street zip classVars classInstVars poolDictionaries inDictionary UserGlobals constraints street String zip Integer instancesInvariant false isModifiable false 3 18 GemStone Systems Inc March 2006 Using the GemStone Programming
257. rent libraryName libraryName See Appendix A Configuring GemBuilder for more information on this setting To determine the correct client library name to use for your GemStone S server product and version see the GemBuilder for Smalltalk Installation Guide 2 2 GemStone Sessions An application connects to the GemStone object server by logging in to the server and disconnects by logging out Each logged in connection is known as a session and is supported by one Gem process The Gem reads objects from the repository executes GemStone Smalltalk methods and propagates changes from the application to the repository Each session presents a single user view of a multiuser GemStone repository Most applications use a single session per client but an application can create multiple sessions from the same client one of which is the current session at any given time You can manage GemStone sessions either through your application code or through the Session Browser GemStone Systems Inc March 2006 Communicating with the GemStone Object Server GemStone Sessions RPC and Linked Sessions A Gem can run as a separate operating system process and respond to Remote Procedure Calls RPCs from its client in which case the session it supports is called an RPC session On platforms that host the GemStone object server and its runtime libraries one Gem can be integrated with the application into a single operating system proc
258. rently for development or debugging control details of the user interface and tune your program for performance These settings are listed in the following table and are described in subsequent sections Table A 1 Configuration Parameters for GemBuilder Parameter Legal values Default alwaysUseGemCursor true false true assertionChecks true false false autoMarkDirty vw 7x only true false true blockingProtocolRpc true false false blockReplicationEnabled true false true blockReplicationPolicy replicate callback replicate March 2006 GemStone Systems Inc A 1 GemBuilder User Manual Table A 1 Configuration Parameters for GemBuilder Parameter Legal values Default bulkLoad true false false confirm true false true connectorNilling true false true connectVerification true false false defaultFaultPolicy immediate lazy lazy deprecationWarnings true false true event PollingFrequency any integer 300 eventPriority any integer 50 faultLevelLnk any integer 2 faultLevelRpc any integer 4 forwarderDebugging true false false freeSlotsOnStubbing true false true generateClassConnectors true false true generateServerClasses true false true generateClientClasses true false true initialCacheSize any integer 5003 initialDirtyPoolSize any integer 157 libraryName any string empty string pollForAsynchrono
259. requires them they are retrieved transparently Managing Interobject Dependencies Replication specs are ordinarily an optimization mechanism Some applications however require a replication spec to function correctly If the structural initialization of an object depends on other objects you must implement replication specs to ensure that when GemBuilder replicates an object it also replicates those objects it depends on For example in order to create a Dictionary when replicating it from the server we need to be able to send hash to each key to determine its location in the hash table hash values aren t necessarily the same in the server as they are in the client So if GemStone replicates a Dictionary it must also replicate the association and the key in the association The default implementation for Dictionary class gt gt replicationSpec therefore contains indexable_part min 1 and Association class gt gt replicationSpec contains key min 1 This works for Dictionaries with simple keys such as strings symbols or integers If an application has dictionaries with complex keys though additional replication specs can be required For example if you are storing Employees as keys in a dictionary and you ve implemented and hash in Employee to consider the firstName and lastName then you must ensure that when a dictionary containing Employees is traversed so are the associations the employees and the firstName an
260. rits its replication spec from its superclass If you haven t changed any of the replication specs in an inheritance chain then the inherited behavior is to replicate all instance variables as specified by the configuration parameters faultLevelLnk and faultLevelRpc To modify a class s replication behavior in precise ways implement the class method replicationSpec For example suppose you want class Employee s address instance variable always to fault in as a forwarder Example 5 5 Employee gt gt replicationSpec super replicationSpec address forwarder To ensure that replication specs established in superclasses remain in effect Example 5 5 appends its implementation to the result of super replicationSpec Appended to the inherited replication spec are nested arrays each of which pairs an instance variable with an expression specifying its treatment at faulting instVar whenFaulted instVar can be either e the client side name of an instance variable or e the reserved identifier indexable_part specifying an object s unnamed indexable instance variables such as the elements of a collection whenFaulted is one of stub faults in the instance variable as a stub forwarder faults in the instance variable as a forwarder to the server 5 22 GemStone Systems Inc March 2006 Sharing Objects Replicates min 1n faults in the instance variable and its referents as replic
261. rity The priority of the Smalltalk process that responds to GemStone events that is the priority at which the block will execute that was supplied as an argument to the keyword gemSignalAction notificationAction or signaledAbortAction These keywords occur in messages used by Gem to Gem signaling changed object notification or when GemStone signals you to abort so that it can reclaim storage respectively faultLevelLnk The default number of levels to replicate an object from GemStone to client Smalltalk in a linked session faultLevelRpc The default number of levels to replicate an object from GemStone to client Smalltalk in a remote session forwarderDebugging When true forwarders support debugging by responding to some basic messages locally such as printOn instVarAt and class which returns GbsForwarder When false these messages are forwarded to the GemStone server object freeSlotsOnStubbing When true stubbing an existing replicate causes all persistent named March 2006 GemStone Systems Inc A 5 GemBuilder User Manual instance variables that is those that will be faulted in when the stub is unstubbed and all indexable instance variables to be set to nil allowing stubs and their potentially outdated instance variables to be garbage collected if they become eligible When false GemBuilder does not alter instance variable values To override this behavior on a class by class basis reimplement
262. rks 5i there is a GemStone specific tool Opening the Settings Browser To open the Settings Browser select Tools gt Settings from the GemStone menu Under VisualWorks 7 x you may also use System gt Settings from the VisualWorks Launcher and scroll down to see all the GemStone configuration settings categories A 8 GemStone Systems Inc March 2006 Configuring GemBuilder The VisualWorks 7 x Settings Browser Figure A 1 The VW7 Settings Browser Summary ST Tools 00 Browser 9 Database Apply Default Settings Debugger E Workspace Current Settings Gem Stone i GbsConfiguration default P Cache Tuning gt Y GemStone L Class Generation libraryName gcilw61 dll Connectors yourself y Debugging P Replication Unapplied Settings Y Server Communic GbsConfiguration default ie A libraryName gcilw61 dll 50 Store yourself 3 Default Package Prerequisites Parameter Categorization The VisualWorks 7 x Settings Browser categories the parameters under headings Selecting each heading allows you to update a set of related configuration parameters Table A 2 VW7 Settings Browser Categorization Cache Tuning bulkLoad initialCacheSize initialDirtyPoolSize Class Generation generateClassConnectors generateServerClasses generateClientClasses March 2006 GemStone Systems Inc A 9 GemBuilder User Manual T
263. rmance Tuning Optimizing Space Management the number of levels to replicate when updating an object from GemStone to the client Smalltalk A level of 2 means to replicate the object and each object it references stubbing objects beyond that level A level of 0 indicates no limit that is entering 0 prevents any stubs from being created The default for the linked version is 2 the default for the RPC version is 4 To examine or change this parameter choose GemStone gt Browse gt Settings and select the Replication tab in the resulting Settings Browser NOTE Take care when using a level of 0 to control replication GemStone can store more objects than can be replicated in a client Smalltalk object space Preventing Transient Stubs If the default faultLevelLnk or faultLevelRpc is the only mechanism used to control fault levels it is possible to create large numbers of stubs that are immediately unstubbed To prevent stubbing on a class basis reimplement the replicationSpec class method for that class For details see Replication Specifications on page 5 21 Setting the Traversal Buffer Size The traversal buffer is an internal buffer that GemBuilder uses when retrieving objects from GemStone The larger the traversal buffer size the more information GemBuilder is able to transfer in a single network call to GemStone To change its value send the message GbsConfiguration current traversalBufferSize aSmalllnteger You
264. rresponding server objects March 2006 GemStone Systems Inc 1 3 GemBuilder for Smalltalk GemBuilder User Manual e use GemStone s programming tools to develop GemStone server classes and methods to operate on your application objects and e perform certain system functions such as committing transactions and starting or ending GemStone sessions The Programming Interface Your client Smalltalk application creates a GemStone session by using GemBuilder to log in to GemStone creating a Gem process to serve your application Many Gem processes can actively communicate with a single repository at the same time As Figure 1 1 illustrates several applications can work concurrently with a single repository with each application viewing the repository as its own GemStone coordinates transactions between each of the applications and the repository Transparent Access to GemStone The interface between your client Smalltalk application and GemStone can be relatively seamless Many of the classes in the base client Smalltalk image are mapped to comparable GemStone server classes and additional class mappings can be created either automatically or explicitly GemBuilder is also able to automatically generate GemStone server classes from client classes and vice versa as necessary Your client objects can be replicated in the GemStone server and GemStone server objects can be replicated in client Smalltalk The simplest way
265. rtedFloatError GsiUnsupportedFloatError GemStone Systems Inc March 2006 Exception Handling Handling Exceptions The subclasses of GbxAbstractControlInterrupt are exceptions raised by the GemStone server that are normally used to invoke a debugger Applications do not typically define handlers for these exceptions The subclasses of GbsGemStoneError are exceptions that are raised by the GemStone server The subclasses of GbsInterfaceError represent client side only GBS errors that is errors that are detected by the GBS client 9 2 Handling Exceptions You can use the on do method to install error handlers to anticipate specific GemStone errors For example this shows how to use the exception classes to handle a GemStone server error Example 9 1 GBSM currentSession evaluate 5 0 on GbsNumErrIntDivisionByZero do ex ex proceedWith oops To handle an entire set of errors rather than an individual error set up the handler for the common superclass of the errors you want to handle For example to handle all GemStone fatal errors set up a handler for GbsFatalError something like this Ps on GbsFatalError do sex ll Each exception detected by the GemStone server also has an associated instance of the class GbsError This is primarily for internal use by GemBuilder but you can examine the GbsError by sending originator to the exception instance For e
266. s Documentation for GemBuilder for Smalltalk is provided in PDF format This is the same documentation that is included with your GemBuilder for Smalltalk product Release Notes and Install Guides for your product software are provided in PDF format in the Documentation section Downloads and Patches provide code fixes and enhancements that have been developed after product release Most code fixes and enhancements listed on the GemStone Web site are available for direct downloading Bugnotes in the Learning Center section identify performance issues or error conditions that you may encounter when using a GemStone product A bugnote describes the cause of the condition and when possible provides an alternative means of accomplishing the task In addition bugnotes identify whether or not a fix is available either by upgrading to another version of the product or by applying a patch Bugnotes are updated regularly TechTips also in the Learning Center section provide information and instructions for topics that usually relate to more effective or efficient use of GemStone products Some Tips may contain code that can be downloaded for use at your site Community Links provide customer forums for discussion of GemStone product issues Technical information on the GemStone Web site is reviewed and updated regularly We recommend that you check this site on a regular basis to obtain the March 2006 GemStone Systems Inc vii
267. s Menu in GemStone Browser Continued remove create access create in ST compile in ST Pop up Text Pane Menu Remove the selected class Creates methods for accessing and updating the instance variables of the selected class Creates a client Smalltalk class having the same name and structure as the selected GemStone Smalltalk class if one doesn t already exist If it does exist executing this menu item has no effect Creates a client Smalltalk class having the same name and structure as the selected GemStone Smalltalk class and compiles all currently defined methods for the class If necessary a notifier lists any methods that cannot be compiled in client Smalltalk A pop up menu appears in any text pane when you press the operate mouse button This menu provides the same commands as the corresponding menu in the client Smalltalk browser s text pane In addition it contains menus for displaying executing inspecting and filing in GemStone Smalltalk code and for using breakpoints in GemStone Smalltalk code The GemStone specific commands available from a text area pane are shown in Table 3 4 Table 3 4 Pop up Menu in GemStone Browser s Text Pane GS Do it Executes the code in GemStone GS Print it Executes the code in GemStone and displays the result in the text area GS Inspect it Executes the code in GemStone and opens an inspector on the result set break Sets a breakpoint at the step point ne
268. s are sampled and archived every 5th time This value is configurable by sending GBSM cacheSampleIntervalMultiplier anInteger This value times statsamplelnterval is the interval between two cache statistics samples For example with the default cacheSampleIntervalMultiplier of 5 and the default statSamplelnterval of 2000 milliseconds the cache statistics will be sampled and archived every 10000 milliseconds or once every 10 seconds A March 2006 GemStone Systems Inc 11 5 Selecting the Locus of Control GemBuilder User Manual VSD cacheSamplelntervalMultiplier of 1 would mean that cache statistics will be sampled and archived every time the main statistics are sampled The Visual Statistics Display tool VSD is provided with the GemStone server product and can be found in the directory SGEMSTONE bin vsd However the version of VSD that is shipped with earlier versions of the GemStone S 6 x or GemStone S 2G server product is incompatible with the GBS statistics archive format The version of VSD that is shipped with the GemStone S 64 Bit server can be used to read GBS statistics files You can download the latest version of VSD from http support gemstone com gemstone_s downloads add_ons vsd4 index htm To view one or more GBS statistics files invoke vsd with the statistic files as arguments See the help system in VSD for more information 11 2 Selecting the Locus of Control By default GemBuilder executes co
269. s in the VW7 Settings Browser 2 A 10 Table A 4 Buttons in the VW5i Settings Browser o oo A 12 xxii GemStone Systems Inc March 2006 Chapter Basic Concepts This chapter describes the overall design of a GemBuilder application and presents the fundamental concepts required to understand the interface between client Smalltalk and the GemStone object server The GemStone Object Server introduces GemStone and its architecture and explains the part each component plays in the system GemBuilder for Smalltalk outlines the basic features of GemBuilder that allow you to access GemStone objects from your Smalltalk application and describes the basic programming functions that GemBuilder provides Designing a GemStone Application an Overview outlines the basic steps involved in producing a client server application with GemBuilder March 2006 GemStone Systems Inc 1 1 The GemStone Object Server GemBuilder User Manual 1 1 The GemStone Object Server The GemStone object server supports multiple concurrent users of a large repository of objects GemStone provides efficient storage and retrieval of large sets of objects resiliency to hardware and software failures protection for object integrity and a rich set of security mechanisms The GemStone object server consists of three main components a repository for storing persistent shared objects a monitor process called th
270. s instances of B Depending on circumstances this may be desirable If it is not e You can implement the method a in class B B gt gt as newValue a newValue March 2006 GemStone Systems Inc 5 13 Replicates GemBuilder User Manual You must then ensure that all modification to instance variable a occur by sending the message a Instances of A thereby don t incur an unnecessary markDirty overhead while instances of B are always marked dirty when a is assigned a new value Marking Instances of Kernel Classes Because some kernel classes are heavily used by the client Smalltalk image you might choose not to make them fully transparent While the overhead for markDirtyOnInstvarAssign is usually not noticeable configuring a kernel class such as Array with markDirtyOnAtPut can slow the system dramatically An alternative to making a kernel class transparent is to create a subclass of the kernel class and send makeGSTransparent to it then use instances of this class in your application instead of the kernel class Marking Modified Objects Dirty Manually Generally we recommend you use the automatic mechanisms described above You can instead if you wish mark objects dirty explicitly in your code The automatic mechanism is usually faster the exception is VisualWorks 5i and much more reliable if you miss even one place where a shared object is modified your application will misbehave To manu
271. segment knows who its owner is and which repository it is associated with A segment also knows if any groups are associated with it However a segment doesn t know who the members of these groups are it knows only what type of access read write or none these groups have to the objects that reference it A segment also doesn t know which objects it controls instead each GemStone server object knows to which segment it has been assigned In other words while segments know their authorization attributes they do not store references to the objects that are assigned to them That information is stored in the objects For example suppose a segment specifies that only its owner has write access to objects and everyone else is limited to read access When the segment s owner creates an object associated with that segment only the owner will be able to modify that object everyone else will have read only access Whenever a program tries to read or write an object GemStone compares the authorization characteristics of the segment with the characteristics of the user who is attempting to do the reading or writing If those characteristics match the operation proceeds If not GemStone returns an error notification Because each object has separate authorization each object must be assigned separately This per object authorization is useful during multiuser development because there might be some objects that you want to share and oth
272. ser Manual You can bypass the migration destination or migrate instances of classes for which no migration destination has been specified by specifying the destination directly in the message that performs the migration The following messages defined in class Class specify a one time only operation that ignores any preset migration destination class migrateInstances aCollectionOfInstances to DestinationClass migrateInstancesTo DestinationClass The migrateInstances to message migrates specified instances to a class the migrateInstancesTo migrates all instances of the receiver to a class Things to Watch Out For There are a few things that you should be aware of when migrating objects e You cannot send a migrate message to self Attempting to do so generates an error that reports The object you are trying to migrate was already on the stack e You cannot migrate instances that you are not authorized to read or write e You need to be aware that the instance variable map used in migrating instances from one GemStone class to another is not the same as the instance variable map described in Chapter 5 whose purpose is to map instance variables from GemStone to Smalltalk Instance Variable Mapping in Migration GemStone supports instance migration between two classes that belong to the same class history For simple migrations such as the addition or removal of an instance variable GemStone provides a de
273. sets separate ones for global connectors and each named kind of session each uniquely defined set of session parameters Two connectors are considered equal if they resolve to the same client object Client Smalltalk sets eliminate duplicates based on equality Therefore NOTE Adding a global or session connector that points to the same object as an existing connector will remove the existing connector Duplicate session connectors are not removed if they are stored in different sessions GemBuilder provides a configuration parameter connect Verification that when true causes connectors to verify at login that they are not redefining a connector that already exists In addition class connectors verify that the two classes they are connecting have compatible structures If a connector fails verification GemBuilder issues a notifier if verbose is also true or raises an exception otherwise You can set connect Verification in the Connector Browser or in the Settings Browser NOTE Under certain circumstances GemBuilder may verify that a connector still exists in a session after it has been explicitly removed from that session This is because the order in which connectors are connected at login is not deterministic For more information and a work around see Connection Order on page 6 8 Initializing At login a connector associates an object in a single user image with an object in a multiuser repository The value of either
274. ss on page 8 13 NOTE Be careful when changing the authorizations on any segment that a user may be using as a current segment or a default segment If you want to add group access to a segment select add from the pop up menu in a Group Name cell Similarly to remove group access from a segment select remove from the pop up menu March 2006 GemStone Systems Inc 8 13 GemStone Administration Tools GemBuilder User Manual In addition you can select groups and users here to be the receiver of actions on the menus Segment Tool Menus The following sections describe the menus that are available in the Segment Tool The File Menu Use the File menu to commit work done in the Segment Tool to abort the transaction to update the tool s view of segments groups and users in the current session and to close the Segment Tool Table 8 1 File Menu in the Segment Tool Commit Commits all the work executed in GemStone during the current transaction After you commit you are given a new updated view of the repository and you can continue your work Abort Cancels all changes that you have made anywhere in GemStone since your last commit After you abort the transaction you are given anew updated view of the repository and you can continue your work Update Updates the information in the Segment Tool and gives you a new updated view of segments groups and users that reflects the most r
275. statistics called main statistics and cache inventory statistics The main statistics of GBS are statistics associated with the session manager and with each logged in session The session manager statistics are Table 11 1 Session Manager Main Statistics Statistic Description numSessions The number of logged in GbsSessions sessionListProtectinvocations The number of accesses to the sessionListProtect semaphore cInterfaceAccessProtectinvocations The number of accesses to GBSM s clnterface semaphore gciCallProtectInvocations The number of accesses to the GciCallProtect semaphore a GbxClnterface shared variable stObjectCacheSizes The number of entries in the stObjectCache mainStatSampleTime The amount of time spent sampling manager and session main statistics cacheStatSampleTime The amount of time spent sampling cache statistics The statistics associated with each logged in session are Table 11 2 Session Main Statistics Statistic Description gciCallsToGem The number of gci calls made that communicate with the gem gciCallsToGemTime The amount of time spent in gci calls that communicate with the gem traverseCalls The number of traversal calls all types including more traversal traverseCallTime The amount of time spent in traversal calls March 2006 GemStone Systems Inc 11 3
276. t e Identify the user account to which you wish to connect e Log in and log out e List active sessions e Designate a current session e Send messages to specific sessions Three GemBuilder classes provide these session control capabilities GbsSession GbsSessionParameters and GbsSessionManager GemStone Systems Inc March 2006 Communicating with the GemStone Object Server Session Control in GemBuilder GbsSession An instance of GbsSession represents a GemStone session connection A successful login returns a new instance of GbsSession You can send messages to an active GbsSession to execute GemStone code control GemStone transactions compile GemStone methods and access named server objects GbsSessionParameters Instances of GbsSessionParameters store information needed to log in to GemStone This information includes the Stone name your user name passwords and the set of connectors to be connected at login GbsSessionManager There is a single instance of GbsSessionManager named GBSM Its job is to manage all GbsSessions logged in from this client support the notion of a current session explained in the following section and handle other miscellaneous GemBuilder matters Whenever a new GbsSession is created it is registered with GBSM GBSM shuts down any server connections before the client Smalltalk quits Defining Session Parameters To initiate a GemStone session you must first identify t
277. t any given time Given a specific root object however it s always possible to determine the exact effect of a set of replication specs Customized Flushing and Faulting You can customize both flushing and faulting to change object structure arbitrarily if your application requires it You can even create a class in the server GemStone that maps to a client Smalltalk class with a different format for example a format of bytes on the client but pointers in the server Modifying Instance Variables During Faulting You can customize object retrieval by using buffers for the client counterparts of GemStone server objects as they are faulted in You can then process the contents of these buffers in any manner required To provide these buffers reimplement the class methods namedValuesBuffer indexableValuesBuffer To unpack these buffers correctly reimplement the class methods namedValues indexableValues namedValues indexableValues By default namedValuesBuf fer returns self new client objects are faulted directly into the named instance variable slots Override this to supply either a different object of the same type or an instance of GbsBuffer a subclass of Array of the required size By default indexableValuesBuffer returns self Override this to return an indexable buffer of the appropriate size March 2006 GemStone Systems Inc 5 27 Replicates GemBuilder User Manual The
278. ter generateClassConnectors is false GemBuilder will still map the classes by name but will not create a connector The difference is that without a connector the mapping only lasts until the session logs out and any other sessions logged in will not have that mapping If a connector is created it is associated with the session parameters object and any session logged in using that session parameters object will have that class mapping created at login time Automatic Class Generation and Mapping By default GemBuilder generates class definitions and connectors automatically as necessary If GemBuilder requires the GemStone server to replicate an instance of a client class that is not already defined on the server then at the first access GemBuilder generates a server class having the same schema and position in the hierarchy and a class connector connecting it to the appropriate client class Conversely if the client must replicate an instance of a GemStone class that is not already defined in client Smalltalk GemBuilder generates the client Smalltalk class and the appropriate class connector If superclasses are also undefined GemBuilder generates the complete superclass hierarchy as necessary You can control automatic class generation with the configuration parameters generateServerClasses and generateClientClasses described starting on page A 6 These settings are global to your image e Ifyou disable automatic generation of GemS
279. that you must either be DataCurator or have certain privileges to perform most of the system administration functions described in this section If you are responsible for GemStone system administration you should refer the chapter on administering user accounts and segments in the GemStone System Administration Guide for specific information on user account management That chapter discusses the privileges you need to manage user accounts and explains how to add and remove users set up user environments change passwords and user privileges and how to add and remove users from groups GemStone User List The GemStone User List window contains a list of all user accounts known to the current repository The administrator can use this window to delete users and as a starting point to add new users and to change the attributes of GemStone users To bring up the GemStone User List from the GemStone menu select Admin gt Users Figure 8 4 shows the GemStone User List March 2006 GemStone Systems Inc 8 23 GemStone Administration Tools GemBuilder User Manual Figure 8 4 GemStone User List Y GemStone User List y oO x File Help Gem Stone User GcUser Nameless System User User Create User Show User Info Delete User Close The GemStone Users List window has two menus File and Help The File menu contains the following items Table 8 9 GemStone User List File Menu Com
280. the replication of GemStone blocks in client Smalltalk Similar restrictions apply with regard to external references and the need for compiler decompiler support Blocks most frequently passed from the server to the client are the sort blocks that accompany instances of SortedCollection and its subclasses Sort blocks rarely have occasion to violate replicated block restrictions If restrictions hamper you consider using block callbacks instead Block Callbacks Block callbacks provide an alternate mechanism for representing a client block in GemStone that avoids the limitations of block replication by calling back into the client Smalltalk to evaluate the block Block callbacks have the following advantages over block replication e Block callbacks don t require a compiler or decompiler e Block callbacks don t suffer the context limitations of block replication The block can reference self super instance variables and non local temporaries it can also perform explicit returns For example the following expression works correctly as a block callback but fails if you try to replicate the block aForwarder at aKey ifAbsent nil asBlockCallback Block callbacks have the following disadvantages e A block that is evaluated many times in GemStone will perform poorly as a block callback For example the following expression sends a message to the client forwarder for each element of the collection represented by aForwar
281. the system or change passwords Privileges are associated with only a few methods and cannot be extended to others For more information about security in general and about the above mechanisms in particular see the relevant chapter of the GemStone Programming Guide For more specific information about privileged methods see the chapter of the GemStone System Administration Guide that discusses common system operations March 2006 GemStone Systems Inc 8 3 Classes for Controlling Access to Objects GemBuilder User Manual 8 2 Classes for Controlling Access to Objects There are three key classes that cooperate in providing access control at the object level Repository Segment and UserProfile This section describes how these classes interact to maintain control of access to objects in an application Repository All disk space used by GemStone that is your entire object store is represented as a single instance of class Repository Committing an object consigns it to that repository as a member of a segment When your system is first delivered GemStone s repository maps to a single file called extent 0 db whose name and physical location can be controlled by the GemStone system administrator with operating system commands and configuration files In GemStone the name of the initial repository object is SystemRepository The repository s name can be changed by the system administrator or anyone with equivalent aut
282. their associated server object To do so GemBuilder must know about the structure of the two objects and the mapping between those structures GemBuilder manages this mapping on a class basis each replicate must be an instances of a class whose definition is mapped to the definition of the corresponding class in the server object space GemBuilder handles many obvious cases automatically but nonstandard mappings require you to implement certain instance and class methods Nonstandard mappings are discussed starting on page 5 15 March 2006 GemStone Systems Inc 5 9 Replicates GemBuilder User Manual Synchronizing State After a relationship has been established between a client object and a GemStone server object GemBuilder keeps their states synchronized by propagating changes as necessary When an object changes in the server GemBuilder automatically updates the corresponding client Smalltalk replicate By default GemBuilder also detects changes to client Smalltalk replicates and automatically updates the corresponding server object The stages and terminology of this synchronization are as follows e When an object is modified in the client leaving its server counterpart out of date the client object is now referred to as dirty When the state of dirty client objects is transferred to their corresponding server objects this is called flushing e When a server object is modified in the server leaving its c
283. tification 7 17 B 1 changing cache size 11 12 connector initialization 6 19 initial cache size 11 12 postconnect action 6 19 schema 10 2 class versions and 10 6 shared data 5 10 7 10 choosing the locus of execution 11 7 circular constraints 3 11 class 5 3 connector 6 7 A 6 connection order 6 8 connector updating 5 4 customizing faulting 5 22 filing out 3 18 generating automatically 5 4 5 5 A 6 mapping 1 4 10 6 mapping to one with a different storage format 5 31 migrating instances to a new version 10 2 nonforwarding 6 6 reduced conflict 7 16 structure matching on client and server 5 3 updating definitions with connectors 6 6 versions and replication specifications 5 23 versions of 10 2 class instance variable connector 6 7 class variable connector 6 7 Classes pane in GemStone Browser 3 5 clearCommitOrAbortReleaseLocksSet System 7 15 clearCommitReleaseLocksSet System 7 15 client forwarder 5 6 Client Libraries 2 2 code pane menu for 3 8 collections with instance variables replicating 5 36 commit GbsSession 7 4 commit command 3 6 commitAndReleaseLocks System 7 15 committing a transaction 1 4 performance 7 16 and flushing compared 5 11 changes to the repository 7 4 compile in ST 10 9 compile in ST command in GemStone Browser s Class menu 3 8 compiling a class definition 3 12 changes to for automatic object synchronization 5 12 in a runtime application B 2 compressing traversal data for
284. tone User List o ooo o 8 24 Figure 8 5 GemStone User Dialog o ooo 8 26 Figure 8 6 Privileges Dialog in GemStone User Window 8 28 Figure 10 1 The Class Version Browser 2 oo o e 10 7 Figure 11 1 Employee Set Faulted into the Client Smalltalk 11 10 Figure A 1 The VW7 Settings Browser Summary A 9 Figure A 2 The VW5i Settings Browser Summary o oo A 11 XX GemStone Systems Inc March 2006 List of Tables Table 3 1 Table 3 2 Table 3 3 Table 3 4 Table 3 5 Table 5 1 Table 5 2 Table 5 3 Table 5 4 Table 5 5 Table 6 1 Table 6 2 Table 6 3 Table 6 4 Table 7 1 Table 8 1 Table 8 2 Table 8 3 The GemStone Menu o o 3 2 Symbol List Menu in GemStone Browser o 3 6 Class Menu in GemStone Browser o o o 3 7 Pop up Menu in GemStone Browser s Text Pane 3 8 Additional GemStone Menu lteMS 3 9 Delegate Conversion Protocol ooo oo 5 39 Forwarder to the Server Conversion Protocol 5 39 Replicate Conversion Protocol ooo oo oo 5 40 Stub Conversion Protocol o o o o eee 5 40 Conversion Protocol for Unshared Client Objects 5 41 Group List Menu in the Connector Browser 6 17 Connectors Menu in the Connector Browser 6 17 O
285. tone classes by setting generateServerClasses to false situations that would otherwise GemStone Systems Inc March 2006 Sharing Objects Class Mapping generate a server class instead raise the exception GbsClassGenerationError e If you disable automatic generation of client Smalltalk classes by setting generateClientClasses to false situations that would otherwise generate a client Smalltalk class instead raise the exception GbsClassGenerationError e You can disable class connector generation by setting generateClassConnectors to false Ifyou do so GemBuilder generates classes but not their corresponding connectors GemBuilder deposits automatically generated GemStone server classes in the GemStone symbol dictionary UserClasses which it creates if necessary Automatically generated client Smalltalk classes are deposited in the current package Automatic class generation is primarily useful as a development time convenience In an application runtime environment we recommend having all necessary classes predefined in both object spaces and having a connector defined for each class before logging in This can improve performance by avoiding unnecessary work when the class is first accessed Schema Mapping By default when you map a client class to a GemStone server class GemBuilder automatically maps all instance variables whose names match regardless of the order in which they are stored You can change this
286. transmission Index 2 GemStone Systems Inc March 2006 GemBuilder User Manual A 8 concurrency modes setting 7 12 optimistic control 7 11 pessimistic control 7 11 7 12 concurrent transactions managing 7 10 ias anio parameters A 1 A 8 alwaysUseGemCursor A 1 A 3 assertionChecks A 1 A 3 autoMarkDirty A 1 A 3 blockingProtocolRpc A 1 A 3 blockReplicationEnabled 5 32 A 1 A 3 blockReplicationPolicy A 1 A 4 bulkLoad A 2 A 4 confirm A 2 A 4 connectorNilling 5 9 A 2 A 4 connectVerification A 2 A 4 defaultFaultPolicy 5 20 A 2 A 5 deprecationWarnings A 2 A 5 eventPollingFrequency A 2 A 5 eventPriority A 2 A 5 faultLevelLnk A 2 A 5 faultLevelRpc A 2 A 5 forwarderDebugging A 2 A 5 freeSlotsOnStubbing A 2 A 5 GemStone CONCURRENCY_MODE 7 12 8 1 STN_GEM_ABORT_TIMEOUT 7 8 generateClassConnectors 5 5 A 2 A 6 generateClientClasses 5 4 A 2 A 6 generateServerClasses 5 4 A 2 A 6 initialCacheSize A 2 A 6 initialDirtyPoolSize A 2 A 6 libraryName A 2 A 6 pollForAsynchronousEvents A 2 A 7 pollForRpcResponse A 2 A 7 removelnvalidConnectors A 2 A 7 rpcSocketWaitTimeoutMs A 2 A 8 setting and examining A 3 stubDebugging A 2 A 8 traversalBufferSize 11 9 A 2 A 8 traversalCompression A 2 A 8 verbose A 2 A 8 confirm configuration parameter A 2 A 4 conflicts in transactions reducing and performance 7 16 write write and RcQueue 7 17 Connected command in Connector Browser 6 6 6 19
287. two levels are replicated object e and its immediate instance variable a fault level is a global parameter Faulting in Changes From Other Sessions Now suppose another session commits a change to b Each session maintains its own view of the GemStone object server s shared object repository The session s private view can be changed by the client application March 2006 GemStone Systems Inc 5 19 Replicates GemBuilder User Manual when it adds removes or modifies objects that is you can see your own changes to the repository or the Gem can change your view at transaction boundaries or after a session has executed GemStone Smalltalk A Gem maintains a list of repository objects that have changed and notifies GemBuilder of any changes to objects it has replicated If it finds any changed counterparts it updates the client object with the new GemStone value Replicates and stubs respond to the message fault Policy The default implementation returns the value of GemBuilder s configuration parameter defaultFaultPolicy either lazy or immediate e A lazy fault policy means that when GemBuilder detects a change in a repository object it turns the client counterpart from a replicate into a stub The object will remain a stub until it next receives a message e An immediate fault policy means that when GemBuilder detects a change in a repository object it updates the replicate immediately If another sessi
288. unterpart the value of that variable is not replicated in the client When GemBuilder flushes the object into the server the server object s suppressed instance variable remains unchanged March 2006 GemStone Systems Inc 5 15 Replicates GemBuilder User Manual You can also suppress instance variable mappings by implementing the client class method instVarMap Example 5 2 shows a simple implementation Example 5 2 TestObject class gt gt instVarMap super instVarMap nil gsName stName nil The first component of the return value a call to super instVarMap ensures that all instance variable mappings established in superclasses remain in effect Appended to the inherited instance variable map an array contains the pairs of instance variable names to map The first pair nil gsName specifies that the server instance variable gsName will never be replicated in the client The second pair stName nil specifies that the client instance variable stName will never be replicated in the server Nonmatching Names You can also specify an explicit instance variable mapping between the server and the client e to map two instance variables whose names don t match or e to prevent the mapping of two instance variables whose names do match In this way your application can accommodate differing schemas To specify nonstandard instance variable mappings use the same class method instVarMap as in Example 5 3
289. untime B 1 GbsRuntime parcel 1 9 GbsServerClass 5 7 GbsSession 2 5 reference to parameters 2 10 GbsSessionManager 2 5 GbsSessionParameters 2 5 instance creation 2 6 GbsSessionParameters class instance creation 2 6 GbsTools B 1 GbsTools parcel 1 9 Gem service name 2 6 signaling another Gem 7 18 user process 1 2 1 3 GemBuilder overview 1 3 GemBuilder tools Breakpoint Browser 4 8 Classes Browser 3 4 3 9 Connector Browser 6 16 6 20 debugger 4 9 GemStone menu 3 2 overview iii 1 6 Segment Tool 8 11 8 19 Session Browser 2 8 2 13 Session Parameters Editor 2 8 Symbol List Browser 8 20 8 23 System Workspace 3 9 User Account Management Tools 8 23 8 29 GemStone documentation 1 v GemStone Browser 3 4 Class List pane 3 7 Classes pane 3 5 Method Categories pane 3 5 Symbol List pane 3 5 Index 6 GemStone Systems Inc March 2006 GemBuilder User Manual GemStone inspector 4 2 GemStone Smalltalk comparing with client Smalltalk E 1 debugger 4 9 4 10 features of 1 5 GemStone User List User Account Management Tools 8 23 Gem to Gem notifiers 7 18 generateClassConnectors configuration parameter 5 5 A 2 A 6 generateClientClasses configuration parameter 5 4 A 2 A 6 generateServerClasses configuration parameter 5 4 A 2 A 6 global connectors 6 4 Globals symbol dictionary 8 9 GsInterSessionSignal 7 18 gsObjImp1 5 31 H hierarchy 10 8 immediate fault policy 5 20 indexableSize 5 31 inde
290. ur chances of being in conflict with other users increase with the time between commits and the size of your read and write sets Under optimistic concurrency control GemStone detects conflict by comparing your read and write sets with those of all other transactions committed since your transaction began Running under optimistic concurrency control is the most convenient and efficient mode of operation when e you are not sharing data with other sessions or e you are reading data but not writing or March 2006 GemStone Systems Inc 7 11 Managing Concurrent Transactions GemBuilder User Manual e you are writing a limited amount of shared data and you can tolerate not being able to commit your work sometimes If you take a pessimistic approach you act as early as possible to prevent conflicts by explicitly requesting locks on objects before you modify them When an object is locked other people are unable to lock the object and they cannot optimistically commit changes to the object Also when you encounter an object that someone else has locked you can abort the transaction immediately instead of wasting time on work that can t be committed Locking improves one user s chances of committing but at the expense of other users So you should use locks sparingly to prevent an overall degradation of system performance Still if there is a lot of competition for shared objects in your application or if you can t tolerate
291. usEvents true false false in 7 x ignored in 5i pollForRpcResponse true false false in 7 x ignored in 5i removeInvalidConnectors true false false rpcSocketWaitTimeoutMs any integer 100 stubDebugging true false false traversalBufferSize any integer 250000 traversalCompression true false false verbose true false true A 2 GemStone Systems Inc March 2006 Configuring GemBuilder To determine the current setting of a parameter send the parameter name as a message to GbsConfiguration current For example the following expression returns the current setting of the connect Verification parameter GbsConfiguration current connectVerification false To set a parameter append a colon to the parameter name and send itas a message to the GbsConfiguration instance with the desired value as the argument For example to set the connectVerification parameter send GbsConfiguration current connectVerification true You will probably prefer to use the Settings Browser to view and change the settings of these parameters See The Settings Browser on page A 8 Using Configuration Parameters to Tune Your Application This section describes the configuration parameters and how their settings affect your program alwaysUseGemCursor Used to reduce the number of conditions under which GBS switches cursors When true GBS changes the cursor to the gem cursor during all interactions with the server When false the cursor is only ch
292. user interface Coordinating Transaction Boundaries Multiple processes need to be in agreement before a commit or abort occurs For example suppose two processes share a single GemStone session If one process is in the process of modifying a set of persistent objects and a second process performs a commit the committed state of the repository will contain a logically inconsistent state of that set of objects The application must coordinate transaction boundaries One way to do this is to make one process the transaction controller for a session and require that all other processes sharing that session request that process for a transaction state change The controller process can then be blocked from performing that change until all other processes using that session have relinquished control by means of some semaphore protocol Coordinating Flushing GemBuilder s transparency mechanism flushes dirty objects to GemStone whenever a commit abort GemStone execution or forwarder send occurs Whenever a process modifies persistent objects it must protect against other processes performing operations that trigger flushing of dirty objects to GemStone The risks are that a flush may catch a logically inconsistent state of a single object or might cause GemBuilder to mark an object not dirty without really flushing it To control when flushing occurs perform update operations within a block passed to GbsSession gt gt critical C
293. ve defined a connector for MyGlobal logging back into GemStone reconnects it Now suppose an instance variable of MyGlobal becomes a stub shortly before a session logs out Sending a message to this variable will produce a defunct stub error At next login MyGlobal s connector will fault in the variable You can then retry the message but only by means of a message sent to MyGlobal or another connected object If the application is maintaining a direct reference to the previous defunct stub the error will persist NOTE You cannot proceed from a defunct stub error After you ve encountered this error determined the cause and corrected the problem you must restart the client Smalltalk operation that encountered the defunct stub Replication Specifications By default when GemBuilder replicates an instance of a connected class it replicates all that class s instance variables to the session s specified fault level You March 2006 GemStone Systems Inc 5 21 Replicates GemBuilder User Manual can further refine faulting by class however with specific instructions for individual instance variables Each class replicates according to a replication specification hereafter referred to as a replication spec The replication spec allows you to fault in specified instance variables as forwarders stubs or replicates that will in turn replicate their instance variables to a specified level By default a class inhe
294. w class explicitly you can include the keyword newVersionof in the class definition template or any subclass creation message after instancesInvariant and before isModifiable Ifthe argument to this keyword is a class this method creates the new class as a new version of that class and the two classes share a class history In this way you can make one class a new version of another even if they do not have the same name If the argument to the newVersionOf keyword is nil the new class is created with a new class history If you do not include the newVersionOf keyword the compiler checks to see if another class having the same name already exists If it does the new class is compiled as a new version of the other class and shares its class history If it does not the new class is created with a new class history For more discussion of class versions and histories see the chapter entitled Class Versions and Instance Migration in the GemStone Programming Guide Private Instance Variables Some GemStone kernel classes have private instance variables For example the superclass of GemStone Bag class defines four used by the object manager and primitives to implement features of nonsequenceable collections such as adding indexing structures for efficient querying Private instance variable names begin with an underscore _ When defining subclasses private instance variables cannot be modified or constrained Modifying
295. with the value of a variable having a different name This requires providing an explicit mapping from the instance variable names of the older class to the instance variable names of the migration destination To do this you will need to override the default mapping strategy by reimplementing a class method named instVarMappingTo in your destination class This method is defined in Class to return an instance variable mapping from the receiver s named instance variables to those in the other class but it can be customized in the new class to explicitly map the two different names There also may be times when you need to perform a specific operation on the value of a given variable before initializing the corresponding variable in the class to which the object is migrating For example suppose that you have a class named Point which defines two instance variables x and y These instance variables define the position of the point in Cartesian two dimensional coordinate space Now suppose that you define a class named NewPoint to use polar coordinates The class has two instance variables named radius and angle The default mapping strategy would cause Point objects to completely lose their position because the old and new classes have no instance variables in common This can be handled however by overriding a migration method in NewPoint by defining it to include an operation that transforms the values of x and y into values that can proper
296. xableValueAt 5 30 indexableValueAt put indexableValues 5 29 indexableValuesBuffer 5 27 5 28 inheritance replication specification and 5 22 method 5 28 initial cache size changing 11 12 InitialCacheSize class variable 11 12 initialCacheSize configuration parameter A 2 initialDirtyPoolSize configuration parameter A 2 A 6 initializing connectors 6 5 connectors programmatically 6 11 inspecting in a debugger 4 2 inspector 4 2 instance migration 10 2 instance variables constraining 3 10 direct access causing stub errors 5 18 11 11 in Collections 5 36 mapping 5 5 5 15 in migration 10 4 mapping nonmatching names 5 16 maximum number in a Class 3 12 modifying while faulting 5 27 modifying while flushing 5 29 private 3 15 suppressing replication of 5 15 instancesAreForwarders 5 7 instVarMap 5 16 invariant objects 3 11 K kernel class connecting connectors for 6 8 connecting instances of 6 7 marking instances dirty 5 14 L lazy fault policy 5 20 libraryName setting Client Libraries 2 2 libraryName configuration parameter A 2 linked application 2 3 linked session 2 3 listInstances Repository 10 3 locks 7 10 logging out effect of 7 14 on objects 7 13 releasing 7 15 removing 7 14 March 2006 GemStone Systems Inc Index 7 GemBuilder User Manual setting 7 13 stubbing and 5 19 locus of execution 11 6 logging into GemStone interactively 2 1
297. xample Example 9 2 GBSM evaluate 12 3 at 4 on GbsObjErrBadOffsetIncomplete do ex ex originator inspect March 2006 GemStone Systems Inc 9 3 Handling Exceptions GemBuilder User Manual User defined Errors You can define and signal your own errors in GemStone For more information on how to do this see the GemStone Programming Guide In a GemBuilder application if you want to define a client Smalltalk exception handler for a user defined error you will first need to associate the GemStone error number with a client Smalltalk exception class To do this use the method GbsError class gt gt defineErrorNumber class This only needs to be done once for each user defined error Note that user defined error numbers must be unique and the numbers 1000 6999 are reserved for use by GemStone For example suppose you have created a GemStone user defined error as follows Example 9 3 In GemStone myErrors myErrors LanguageDictionary new UserGlobals at MyErrors put myErrors myErrors at English put Array new 10 myErrors at English at 10 put My new error with argument 1 The following client Smalltalk code signals your newly created error in GemStone GBSM evaluate System signal 10 args 46 signalDictionary MyErrors A generic signal handler for all GemStone errors would trap this signal This code sets up the
298. xii GemStone Systems Inc March 2006 Reserved and Optimized Selectors 3 17 Saving Class and Method Definitions in Files 3 18 Handling Errors While FilingIn 3 20 Chapter 4 Debugging 4 1 Debugging Overview 2 2 o ee 4 1 4 2 TASpectOLs psa de dose se Waste a d we ste doe a ERGs ea Aes 4 2 AS breakpoltsue out hn faye PR eek a A el Sk RN ras ea 4 5 Breakpoints for Primitive Methods o ooo 4 7 Breakpoints for Optimized Methods o o o ooo 4 7 The Breakpoint Browser o ooo e 4 8 44 Debugger sea and da mala rre 4 9 Getting a Stack Trace Without a Debugger 4 10 Chapter 5 Sharing Objects 5 1 Which Objects to Share 2 ee ee 5 2 5 2 Class Mapping ici a et ete a UE ce Meee ot Baye ee 5 3 Automatic Class Generation and Mapping 5 4 Schema Mapping 2 o ee eee 5 5 Behavior Mapping ee 5 5 Mapping and Class Versions ooo o 5 6 5S sFOrwarders id ek neko ee ek ee elt i ede aA a ar 5 6 Sending Messages aoaaa es 5 7 ATE UMENtS oe e oa hee eee ae a NS OE rd da 5 8 RESUS ii htt ao od e at tas ES a he tae AA 5 8 Defunct Forwarders e e a 5 8 DA Replicates prat A a a add anta ox A NE E ET E E 5 9 Synchronizing State aaa aa e 5 10 Faulting Y La AA A A 5 10 AI gh at Rode teases ee aga Anne A 5 11 Marking Modified Objects Dirty
299. y at login that they are not redefining a connector that already exists and class connectors verify that the two classes they are connecting have compatible structures When false these things are not checked Set to true during development unless logging in becomes too slow or your connector definitions are stable GemStone Systems Inc March 2006 Configuring GemBuilder See The Connector Browser on page 6 16 defaultFaultPolicy Specifies GemBuilder s default approach to updating client Smalltalk objects whose GemStone counterparts have changed When lazy GemBuilder responds to a change in a GemStone server object by turning its client Smalltalk replicate into a stub The new GemStone value is faulted in the next time the stub is sent a message When immediate GemBuilder responds to a change in a GemStone server object by updating the client Smalltalk replicate immediately The defaultFaultPolicy is implemented by Object gt gt faultPolicy Subclasses can override this method for specific cases deprecationWarnings When true any attempt to use a deprecated feature of GemBuilder for Smalltalk causes a proceedable exception to be raised Deprecated features may be removed in a future release When false deprecated features may be used with no warning eventPollingFrequency How often in milliseconds that GemBuilder polls for GemStone events such as changed object notification or Gem to Gem signaling eventPrio
300. ymbol list unnamed segments are those that are not referenced in any dictionary or symbol list In addition to the segments displayed in the Segment Tool all users also have read and write authorization to GsIndexing segment Because authorization changes should not be made to that segment however it is not included in the tool NOTE Changes made to cells in the tables are accepted automatically as soon as you either press Return make a selection in a combo box associated with the cell or simply move the focus to another cell or field by moving the mouse If you enter an invalid value in a cell results in a warning and the cell reverts to the original value In the segment definition area of the Tool you can change the following Current You can set the segment to be the current segment the segment to which GemStone will assign any objects you create now Default You can set the segment to be the default segment the home segment that is your current segment when you log in to GemStone Owner Name You can enter any valid user name that already exists in the system To change an owner name type a valid owner name into the cell 8 12 GemStone Systems Inc March 2006 Security and Object Access GemStone Administration Tools Owner Access and World Access To change owner and world access type one of the following values into their cells e read means that a user can read any of the segment s objects but c

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