Tutorial 16 Event Driven Coding
Contents
1. www softwareschule ch creport char counter distribution Put wait a minute As we have seen Windows is a message based operating system System messages are handled by a message handler that translates the message to Delphi event handlers For instance when a user clicks a button on a form Windows sends a message to the application and the application reacts to this new event If the OnClick event for that button TBitBtn Create frmMon2 is specified it gets executed The code to respond to events is contained in Delphi event procedures event handlers All components have a set of events that they can react on For example all clickable components have an OnClick event that gets fired if a user clicks a component with a mouse But the procedure is too tight behind the event it s more flexible to realize a loose coupling between event and event handler by a small footprint like a control layer procedure btnCalcCharsClick Sender TObject begin CharsCalculation calls the procedure indirect end The article How to Detach an Event Handler from a Control Event describes a simple mechanism to remove an event handling procedure from a control s event SF This form example requires no local variables in the method Procedure InitFirstForm Init Second Formby many different classes TMainMenu TMenuItem TPanel and TBitmap Because the most controls are building at runtime on behalf of the with statement with TLabel Cr2. maXbox Starter 16 Start with Event Driven Programming 1 1 Set an Event Today we spend another small time in programming with a new concept called events Most modern programming languages like PHP Python or Ruby are dynamically typed event driven and employ an interpreter for program execution Event driven programming are usually message based languages offering the user an interactive dialog allowing commands that are interpreted and immediately executed like a button click see below We will concentrate for the first on creating an API call of a DLL using PlaySound from the winmm d11 library as the result of a asynchronous timer event But first of all I ll explain you what synchronous and asynchronous events are In fact there are 2 programming models used in event driven applications e Synchronous events e Asynchronous events Some event handlers are called immediately when the event occurs otherwise you have to wait These are called synchronous events An example is CloseButtonClick It gets called as soon as the user hits the close button However some events are called or executed after the event occurs usually after a short amount of idle time With these asynchronous events you don t have to wait so the caller continues without pausing for a response All the windows and dialog boxes in your application are based on the class TForm A VCL form contains the description of the properties of the form
3. 328 procedure CloseButtonClick Sender TObject 329 begin 330 frmMon Close calls the onClose eventhandler 331 end That means onClick gt CloseButtonClick gt frmMon Close gt onClose gt CloseFormClick At its simplest you control the layout of your user interface by where you place controls in your forms The placement choices you make are reflected in the control s Top Left Width and Height properties You can change these values also with Set Bounds in line 458 at runtime to change the position and size of the controls in your forms Controls have a number of other properties however that allow them to automatically adjust to their contents or containers This allows you to lay out your forms so that the pieces fit together into a unified whole 455 with panB do begin 456 Caoicnomg Ys Owiellamer ss Ys 457 Parent frmMon2 458 Set Bounds LEFTBASE TOPBASE 40 340 400 Next event we take a look at is the main calculation procedure fired by an OnClick event behind a TBitBtn declared in the form building see picture 3 on the form 4S2 with TBitBtn Create frmMon2 do begin 433 parent frmMon2 434 SetBounds 297 290 121 30 435 Caption Calculation 436 glyph LoadFromResourceName getHINSTANCE CL_MPSTEP 437 OnClick btnCalcCharsClick 438 end Remember the event handler btnCalcCharsClick is invoked by the event procedure btnCalcCharsClick Sender TObject
4. the threads proceed simultaneously To use a metaphor they are like runners in a race no runner waits for another runner They all proceed at their own rate E Because Synchronize uses a form message loop it does not work in console applications For console applications use other mechanisms such as a mutex see graph below or critical sections to protect access to RTL or VCL objects www softwareschule ch 11 Thread Sorting Demo Rosenheim F xj Bubble Sort Selection Sort 6 3 Threads at work with Log The point is you can combine asynchronous calls with threads For example asynchronous data fetches or command execution does not block a current thread of execution But then your function or object has to be thread safe So what s thread safe Because multiple clients can access for example your remote data module simultaneously you must guard your instance data properties contained objects and so on as well as global variables Tasks for advanced studies LU How can you crack a password with a massive parallel concept Study all about a salt A 512 bit salt is used by password derived keys which means there are 2 512 keys for each password So a same password doesn t generate always a same key This significantly decreases vulnerability to off line dictionary attacks pre computing all keys for a dictionary is very difficult when a salt is used The derived key is returned as a hex or base64 encoded strin
5. 0 caption Pulsar Universe BitmaXx 341 color clblack 342 height 700 343 width 850 344 Show 345 onMousedown ImagelMouseDown 346 onClose CloseFormClick sync with form2 347 end TForm declares and defines a method CloseFormClick which will be invoked at runtime whenever the user presses close button x on the window or lt Alt gt lt F4 gt This procedure is called an event handler line 346 because it responds to events that occur while the program is running The onClose Calls the event handler previously registered www softwareschule ch 6 318 procedure CloseFormClick Sender TObject var Action TCloseAction 319 begin 320 Imagel Free myImage Free 22l Image2 Free 322 frmMon2 Free B23 frmMon Free 324 frmMon NIL S25 Writeln char counter form has been closed at TimeToStr Time 326 end Free Destroy deactivates the form object by setting Enabled to False before freeing the resources required by the form The event handler CloseFormClick in the example deletes the 2 forms after it is closed so the form would need to be recreated if you needed to use a form elsewhere in the application If the form were displayed using Show you could not close the form within the event handler because Show returns while the form is still open So it s better to work with another event handler ButtonCloseClick which calls with a method inFrm Close also the above centralized CloseFormClick
6. 44321 592 582 102918 47 1302464 111813712052 112625961852 706 274 152 174 512 20 Character Count 22756 Text or File I J gt Calculation I Reset Load Text D Kleiner2005 TestApp maxbox2 maxbox2 source_2007 maxbox29 examples 09 _pas_umlrunner_componenttest4 txt is loaded 3 Our App with x events on a second form By default a form owns all components that are on it In turn the form is owned by the application Thus when the application shuts down and its memory is freed the memory for all forms and all their owned components is also freed B Hint Owner is a property of TComponent so you don t have to declare it when passing to the Constructor In our case when dynamically creating one or more components as part of a form the owner has to be the form itself so you refer to the form via the self pointer in line 336 and a reference pointer by yourself inF rm 335 begin 336 frmMon TForm Create self 348 Imagel TImage create frmMon 356 Image2 TImage create frmMon Next we step to the concept of event handlers Once you determine when the event occurs later in the main program you must define how you want the event handled Specifying a second event handler object in line 345 or delegate method causes the first binding to be added with the second simply means the form can handle 2 events 337 with frmMon do begin 338 FormStyle fsStayOnTop 339 Position poScreenCenter 34
7. Delphi class is designed to be used as a storage mechanism for an array of pointers By design each method function or procedure in Delphi code can be represented with a TMet hod Delphi type www softwareschule ch 12 Thread A Mutex Thread B T lock gt r il T lock 1 Thread A locks mutex and does work with shared resource 2 Thread B attempts to lock mutex and blocks unlock 3 Thread A unlocks mutex the shared resource l 4 Thread B wakes locks the mutex and does work with l i AE 7 Areal Thread with a synchronisation object d 7 One note about async execution with fork on Linux with libc commands there will be better solutions execute and wait and so on and we still work on it so I m curious about comments therefore my aim is to publish improvements in a basic framework on sourceforge net depends on your feedback Ke Try to find out more about symmetric asymmetric encryption systems and the probability to crack it Due to their large computational requirements a asymmetric key system is used in practice only for encrypting so called session keys The pay load is encrypted with a symmetric algorithm using the session key This combination of two methods is called hybrid encryption asymme
8. Test it with F2 F9 or press Compile and you should hear a sound and a browser will open So far so good now we ll open the example 287_eventhandling2 txt 20888 kb Or 263_async_sound txt If you can t find the file use one of those links http www softwareschule ch examples 287_eventhandling2 txt http www softwareschule ch examples 287_eventhandling2 htm Or you use the Save Page as function of your browser and load it from examples or wherever you stored it One important thing The mentioned DLL must reside on your harddisk Now let s take a look at the code of this project first with the declaration of the 2 forms Our first line is 1 Program EventHandler_Tutorial We have to name the program it s called EventHandler_Tutorial Next we jump to line 19 16 var LF DROZ SG EXCEpErON 18 Imagel Image2 TImage Lg frmMon frmMon2 TForm First in line 19 we ask to set 2 form variables Forms are important for all IT systems that offer interfaces for user or programming access Particularly this includes machines in the private and commercial sector as well as services like electronics or multimedia In these cases the var declaration is usually done by entering a form name and the according class name Mas we now know TForm is able to handle the events as a window function The Windows API function used to create parent top level and child windows is called CreateWindow The event handler meth
9. URCE SND_ASYNC The following example stops playback of a sound that is playing asynchronously PlaySound NULL 0 0 If you set the flag SND_NOSTOP we get an interesting constellation This specified sound event will yield to another sound event that is already playing If a sound cannot be played because the resource needed to generate that sound is busy playing another sound the function immediately returns FALSE without playing the requested sound If this flag is not specified PlaySound attempts to stop the currently playing sound so that the device can be used to play the new sound again www softwareschule ch 3 Ry Discussion have an app that has a background sound and a sound when someone clicks something But when they click the something sound it stops the background sound which is supposed to loop How can play both sounds and leave the background looping Answer I m 99 sure that the PlaySound API which SoundPlayer Play is wrapping does not support this no matter how you do it You will have to look at something like DirectX or multithreading if you really want to do this I m trying to get the SoundP layer to play two wav files at the same time The documentation says is should play asynchronously but when try it seems to end the play of the first SoundPlayer as soon as the second one starts to play read the documentation and it doesn t imply that it will merge the two sounds merely that the m
10. and the components it owns Each form file or a form code section represents a single form which usually corresponds to a window or dialog box in an application and are able to handle events Every Delphi application must have or provide a main form The main form is the first form created in the body of the application When the main form closes the application terminates Close gt gt J Save Text gt 328 procedure CloseButtonClick Sender TObject 329 begin I EiamMMoin CLOSep 331 end So what s event driven programming Event based programs are organized around the processing of events When a program cannot complete an operation immediately because it has to wait for an event e g the arrival of a packet or the completion of a disk store transfer it registers a callback a function that will be invoked when the event occurs Event based programs are typically driven by a loop that polls for events and executes the appropriate callback when the event occurs This is the famous message loop waiting for events in the window model see below chart2 while GetMessage lpMsg 0 0 0 do begin TranslateMessage lpMsg DispatchMessage 1pMsqg end A callback executes indivisibly until it hits a blocking operation at which point it registers a new callback and then returns So in our close event how does the callback look like onClick CloseButtonClick onClose CloseFormClick As said above we registe
11. e result is more robust software The debate over whether threads or events are best suited to systems software has been raging for decades Threaded programs can be structured as a single flow of control using standard linguistic constructs such as loops across blocking calls Event driven programs in contrast require a series of small callback functions one for each blocking operation Any stackallocated variables disappear across www softwareschule ch 9 callbacks Thus event driven programs rely heavily on dynamic memory allocation and are more prone to memory errors in low level languages such as C and C Ry Types in Events Because it is not necessary to declare types of variables and formal arguments of subroutines these languages are often called type less This approach can be better characterized as dynamically typed because each value in these languages is associated with a data type In many articles they describe the advantages of interpreted dynamically typed languages yet one should be aware of two serious drawbacks Firstly these languages usually perform semantic checks e g for the existence of identifiers when the code is actually executed which leaves many possibilities for typing errors to be undetected Secondly type checks for each operation must be performed at run time This must be done not only once but every time an instruction is executed When performing simple operations like the addition of
12. e it puts the events e g from interrupts or other sources It then sends the messages from that queue to all windows depending on the message e g it won t send key messages to a window that doesn t have focus www softwareschule ch 4 A message is posted to every window that should receive it The OS decides depending on the type of message whether a window should receive that message or not Most messages are waited for by the system i e the message won t get posted to another window until it was processed by the window This has a great impact for broadcast messages if one window doesn t return when handling that message the queue is blocked and other windows won t receive the message anymore dso as far as can see it implies that the API call queues up the sounds to be played and the method returns when your sound starts playing so there s no parallel processing possible So after this hard low level introduction we jump to our app a small form which counts the characters of a text file and deepen our knowledge with events gt Before this starter code will work you will need to download maXbox from the website It can be down loaded from http sourceforge net projects maxbox site Once the download has finished unzip the file making sure that you preserve the folder structure as it is If you double click maxbox3 exe the box opens a default program Make sure the version is at least 3 8 because Modules Count use that
13. eate frmMon2 do begin parent frmMon2 set Bounds 9 250 116 13 Caption Character Count end Next Question will be to show the possibility to share the same event in different controls or in different event handlers Associating an event with an existing event handler in purpose of code reuse Suppose we want to have a button and a menu item do the same thing or in our case a form and an Image to do the same thing by the event onMouseDown of frmMon onMousedown ImagelMouseDown of Imagel onMousedown ImagelMouseDown Delphi and other languages allows one coded event to be assigned to many event handlers as long as the methods are of the same type means they have the same arguments eg sender btn shift x y in mousedown The classic example is the OnClick event which is shared by many components 234 procedure ImagelMouseDown Sender TObject Btn TMouseButton B35 Succe WSimsieSracSer Xx ws limites A 236 var i byte 237 begin BSS M 250 End Vou can then assign this procedure to as many event handlers as you wish Procedure AssignEvents Begin www softwareschule ch 8 MyButton OnClick ClickHandlerComponent MyLabel OnClick ClickHandlerComponent MyCombo Onclick ClickHandlerComponent You Get the message Each time one of these components is clicked the above procedure ClickHandlerComponent is executed This can be useful is certain circumstances but mainly in this t
14. ed to exchange encrypted data with other users in a parallel way but not a parallel function It does not contain functions for key management The keys have to be exchanged between the users on a secure parallel channel In our case we just use a secure password 88 procedure EncryptMediaAES sender TObject 106 with TStopwatch Create do begin Ton Start 108 AESSymetricExecute selectFile selectFilet _encrypt AESpassw 109 mpan font color clblue LLO mpan font size 30 dita mpan caption File Encrypted LLZ Screen Cursor crDefault LLS SEOD 114 clstBox Items Add Time consuming GetValueStr of TARS inttoStr getFileSize selectFile File Size 116 Hnccr 117 end And that s how to get a feeling of the speed of AES with a protocol extract Use native AES 256 cipher and native CBC chaining mode Ciphertext size 21726 bytes Decryption succeeded 21726 bytes processed Speed of decryption was 1326 KiB per second 4 GByte about 40 Minutes M0 understand threads one must think of several programs running at once Imagine further that all these programs have access to the same set of global variables and function calls Each of these programs would represent a thread of execution and is thus called a thread The important differentiation is that each thread does not have to wait for any other thread to proceed If they have to wait we must use a synchronize mechanism All
15. ethod call is asynchronous Internally PlaySound calls the PlaySound API from mmsystem h with the parameters SND_ASYNC and SND_NODEFAULT This means so far that The sound is played asynchronously and PlaySound returns immediately after beginning the sound and No default sound event is used If the sound cannot be found PlaySound returns silently without playing the default sound Tastendruck MouseEvents i Messages Windows Nachrichtenfluss Windowsy x Delphi Program Event Loop procedure VVinMaing while getvlessage do begin translateMessage dispatchMessage Appliction Queue Application Queue function V ndProc window HVVnd Message WParam word LParam longint langint export case Message of wm_Timer begin Fensterfunktion WMTimerBeep Exit Reaktion WMTimerBeep pepanen begin Messa geBeep 0 end API Library Application Programing Interface MK Chart Chart 2 Message Driven Events in Windows In a Win32 64 application we start a message loop that fetches messages from a queue translates them and then dispatches them Eventually each message reaches our WndProc where the associated event can be handled in a case construct So the event is the timer which will be answered be the event handler WMTimerBeep and then executed by the MessageBeep or PlaySound The OS maintains a message or system queue wher
16. g The salt must be a string that uses the same encoding We also use a lot of more multi scripts to teach and the wish to enhance it with a thread simply take a look in the meantime at 141_thread txt 210_public_private_cryptosystem txt and 138_sorting_swap_search2 txt Atleast let s say a few words about massive threads and parallel programming and what functions they perform Do not create too many threads in your apps The overhead in managing multiple threads can impact performance The recommended limit is 16 threads per process on single processor systems This limit assumes that most of those threads are waiting for external events If all threads are active you will want to use fewer Bou can create multiple instances of the same thread type to execute parallel code For example you can launch a new instance of a thread in response to some user action allowing each thread to perform the expected response For events in Win32 Delphi OOP only one method can be assigned as a handler to a component s event But you can build a Win32 Delphi object that maintains a list of the methods its event s is handled by thus creating a simulation of multicast event handling Short a design study First we ll define a simple class TMultiEventClass with only one event of TMultiEvent type In order to store a list of methods that will be called when event is fired using the FireMultiEvent we ll use a fMultiEventHandlers TList object The TList
17. ip it serves to illustrate the main point reduce design time coding by assigning events Also an area where you do have many controls sharing code is in respect to Main Menus Popup Menus and Speed buttons ia Fie Program Options Debug Output Help E a eee a aa o 2 Eg RE Lees Load W Find Replace Refactor Compile UseCase Tutorials i Resources Seri lds ral A AA Ai B ial a Wal w g A P he ie pe 288_bitbit txt v Workbench mx4 F iprogram Bitmap Pulsar BITMAX JpegTester z 3 Loads a bitmap with an aggregation from TPicture Class 4 A function stretches also a bitmap with specified number of pixels 5 in horizontal vertical dimension locs 216 6 7 const MAXP 100 8 FIRSTCOLOR clTeal clPurple 9 KB abcdefghijklmnopqrstuvwxyz 10 ll 12 type i3 TMatrix Array 1 MAXP of TPoint l4 1s var 16 Exc2 Exception Set ciear breakpoint 17 Imagel Image2 image3 image4 TImage Gato Code End F6 18 frmMon frmMon2 frmMon3 TForm ES Clipboard Export 19 udLinie TUpDown Cipboard Import 2a UD TUpDown S Show Interface Ctrl I 21 SB TScrollBar Hola aie 22 TB TTrackBar J Font Size Options 23 panUD TPanel EAE 24 panTB TPanel i HTML Syntax xl maxbox3 E maxbox maxbox3 examples 288_bitblt txt Compiled done 23 06 2012 13 23 04 EF KML syntax sin pi of convert 5 42101086242752E 20 E so syntax E E
18. itecture there are 2 threads categories e Threads with synchronisation blocking at the end e Threads without synchronisation non blocking at all In case you re new to the concept a thread is basically a very beneficial alternative in most cases to spawning a new process Programs you use every day make great use of threads whether you know it or not but you have to program it The most basic example is whenever you re using a program that has a lengthy task to achieve say downloading a file or backing up a database the program on the server will most likely spawn a thread to do that job This is due to the fact that if a thread was not created the main thread where your main function is running would be stuck waiting for the event to complete and the screen would freeze www softwareschule ch 10 For example first is a listener thread that listens and waits for a connection So we don t have to worry about threads the built in thread will be served by for example Indy though parameter TdTCPServerlExecute AThread TIdPeerThread When our DWS client is connected these threads transfer all the communication operations to another thread This technique is very efficient because your client application will be able to connect any time even if there are many different connections to the server The second command CTR_FILE transfers the app to the client Or another example is AES cryptography which is us
19. ntelligible A synchronous event is an event that when fired waits on a response from something called an event handler A function which returns no data has no result value can always be called asynchronously cause we don t have to wait for a result or there s no need to synchronise the functions Let s begin with the application structure process in general of an API call The PlaySound function plays a sound specified by the given file name resource or system event A system event may be associated with a sound in the registry or in the WIN INI file 1 Header Declared in msystem h include Windows h 2 Library Use Winmm d11 or the lib 3 Declaration of the external function 4 Load the DLL and call the API function e Static at start time e Dynamic at run time 5 Unload the DLL loaded DLL c WINDOWS system32 winmm d11 So we call the API function dynamic at runtime and of course asynchronously The sound is played asynchronously and PlaySound returns immediately after beginning the sound To terminate an asynchronously played waveform sound call PlaySound with pszSound set to NULL www softwareschule ch 2 The API call to the function just works fine doesn t have any glitch On the other side a sound is played synchronously and PlaySound returns after the sound event completes This is the default behaviour in case you have a list of songs If you click on the menu lt Debug Modules Count gt yo
20. od must accept four parameters hwna the handle for the window that received the message nMessage the Windows message number and two Integer parameters the contents of which vary depending on the Windows message the documentation for each message describes the values of these parameters 1 3 Event and Event Handler in a Form Typically you create forms for your application from within the IDE with a form designer In maXbox we can code directly and native in the script your form with controls When created this way the forms have a runtime constructor that takes one argument Owner which is the owner of the form being created The owner is the calling application object or form object Owner can be NIL Or copy amp paste www softwareschule ch 5 To pass additional arguments to a form create a separate constructor and instantiate the form using this new constructor The owner of a component is determined by the parameter passed to the constructor when the component is created But there are three or four possibilities passing one Application Self NIL ora Owner by Yourself Word Counter 5 xj Textinput Example of the UML Script in AnalysistDesign of Activity 09 Get the numbers you count and see locs 58 program UMLRunner_Components const LEFTBASE 20 TOPBASE 25 Character Statistic eb fo a fe f_fo fh fi fi fe fr fm fn fo fp fo fr_fs fe fu fv fw fe fy 2 2022 787 922 461 22
21. r a callback CloseButtonClick with the address operator so the callback function will be executed when the event onClick occurs in our case the button is clicked The interesting point is the separation of event and event handler callback routine Ban event handler is a callback routine that operates asynchronously and handles inputs received into a program events In this context an event is some meaningful element of program information from an underlying development framework usually from a graphical user interface GUI toolkit or some kind of input routine On the GUI side events include key strokes mouse activity action selections messages or timer expirations On the input side events include opening or closing files or forms and data streams reading data and so on Now we come to the first API event Hope you did already work with the Starter 1 to 15 available at http www softwareschule ch maxbox htm Remember What makes the event synchronous or asynchronous is whether it s handled synchronously blocking or asynchronously non blocking Non Blocking means that the application will not be blocked when the application plays a sound or a socket read write data This is efficient because your application don t have to wait for a sound result or aconnection Unfortunately using this technique is little complicated to develop a protocol If your protocol has many commands or calls in a Sequence your code will be very uni
22. t apps mediawiki maxbox My Own Experience http www softwareschule ch download armasuisse_components pdf SHA1 Hash of maXbox 3 9 1 2 Win B8686418D5F31B618E595F26F8E74BBCD39AA839 www softwareschule ch 14
23. tric symmetric This implies no security deficit if you use a good random number generator for the session key like a HW generator below try to change a second event handler Image1MouseDown2 one for each event 234 procedure ImagelMouseDown Sender TObject Btn TMouseButton Simities on ee Stec mx wx try to find out more about the callback function schema and the question how it works in a synchronous or asynchronous mode ca Check the source of LockBox to find out how a thread is used www softwareschule ch 13 05 E maxbox maxbox3 source TPLockBoxrun ciphers uTPLb_AES pas try to add change the event handler procedure bt nLoadClick Sender TObject with a second event with a message when the text is loaded 262 procedure btnLoadClick Sender TObject 263 Set a new text file to count 264 var i integer 265 selectedFile string 266 begin 267 edText Text panB Caption 268 SBtnLoad true 269 chk checked false max kleiner com Links of maXbox and Asynchronous Threads of DelphiWebStart 2 059_timerobject_starter2_ibz2_asynec txt 7 Jensen K and Wirth N 1974 PASCAL User Manual and Report Springer http sourceforge net projects delphiwebstart Event driven Programming for Robust Software http pdos csail mit edu rtm papers dabek event pdf http www softwareschule ch maxbox htm http sourceforge net projects maxbox http sourceforge ne
24. two real numbers most of the time for the operation will be spent on verifying the types of the arguments even when it is clear that because of the design of the algorithm no other types may occur While the additional overhead is negligible for interactive execution of commands typed on a command line it has a serious impact on routines that require intensive calculations For ex thread 1 P appends a number to a list and then set the event to notify the consumer The consumer s call to wait stops blocking and the integer is retrieved from the list e Avoiding bottlenecks With only one thread a program must stop all execution when waiting for slow processes such as accessing files on disk communicating with other machines or displaying multimedia content The CPU sits idle until the process completes With multiple threads your application can continue execution in separate threads while one thread waits for the results of a slow process e Organizing program behaviour Often a program s run can be organized into several parallel processes that function independently Use threads to launch a single section of code simultaneously for each of these parallel cases e Multiprocessing If the system running your program has multiple processors you can improve performance by dividing the work into several threads and letting them run simultaneously on separate processors One word concerning a processing thread In the internal arch
25. u can see all the libraries modules loaded by your app and of course also the winmm d11_ with our function PlaySound init 25 function BOOL PlaySound LPCTSTR pszSound HMODULE hmod DWORD fdwSound mX System Modules Library List DOWS system32 imm32 dl DOW S system32 URLMON DLL DOWSisystem32 wininet dll DOW S system32 CRYPT32 dll DOWS system32 MSASN1 dll DOWS system32 shell32 dll DOWS system32 winspool dry DOWS system32 comdlg32 dil DOWS system32 wsock32 dll DOWS system32 wS2_32 dll system32 wS2HELP dll DOWSisystem32 MSCTF dll DOWS system32 UxTheme dil DOWSisystem32 DNSAPI dll 1 Result as of the loaded Modules 1 2 Code Event handling with an API Call As you already know the tool is split up into the toolbar across the top the editor or code part in the centre and the output window shell like a song length protocol result at the bottom Included in the package maXbox is the integrated MP3 Songs utility player as an add on listed on the menu Options Add Ons But we show the tool as a script extract with source an add on is a real compiled and integrated script There is a special function in Win32 which plays wav files You do not need the full Windows Media Control Interface You can either play the sound by mentioning its filename in which case the file needs to be distributed with the program or by making the file into a resource with a line like PlaySound SoundName hInst SND_RESO
26. xc ClassName division zero fault acam 00111101110011001100110011001101 EI CE syntax 13421773 2 Java Syntax 0 100000001490116 0 100000001490116 0 0625 this is E 0 100000001490116 got last exception intern division zero mX3 executed 23 06 2012 13 23 04 Runtime 0 0 0 828 PascalScript maXbox3 RemObjects amp SynEdit Ver 3 9 1 2 391 Work Dir E maxbox maxbox3 examples a Till now we are discussing the topics of sync and async Calls events and the way it processes the calls by the receiver or event handler parallel or not Asynchronous calls or connections allow your app to continue processing without waiting for the process function to be completely closed but not always in a simultaneous mode Therefore we come now to the discussion about real parallel programming with threads multithreading or multiprocessing programming 1 4 Notes about Events or Threads Events are a better means of managing I O concurrency in server software than threads events help avoid bugs caused by the unnecessary CPU concurrency introduced by threads Event based programs also tend to have more stable performance under heavy load than threaded programs We argue that our libasync non blocking I O library makes event based programming convenient and evaluate extensions to the library that allow event based programs to take advantage of multi processors We conclude that events provide all the benefits of threads with substantially less complexity th
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