Multithreaded Application Tutorial/pl

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Kurs tworzenia aplikacji wielowątkowych

Wprowadzenie

Na tej stronie spróbujemy wyjaśnić, w jaki sposób napisać i debugować aplikacje wielowątkowe przy pomocy Free Pascala i Lazarusa. Aplikacja wielowątkowa to program, który tworzy dwa lub więcej wątków wykonawczych działających w tym samym czasie. Jeśli nie miałeś dotąd do czynienia z wielowątkowością, przeczytaj paragraf "Czy potrzebujesz wielowątkowości?" aby ustalić, czy jest ci to naprawdę potrzebne, bo być może zaoszczędzisz sobie bólu głowy.

Pierwszy wątek nazywany jest głównym wątkiem. Główny wątek to ten, który jest tworzony przez System Operacyjny, to ten sam, w którym nasza aplikacja rozpoczyna działanie. Główny wątek musi być jedynym wątkiem, który aktualizuje komponenty do komunikacji z użytkownikiem: w przeciwnym wypadku, aplikacja może się zawiesić.

Podstawowym założeniem jest to, aby aplikacja mogła przetwarzać dane w tle, tj. w drugim wątku, podczas gdy użytkownik może kontynuować pracę przy użyciu głównego wątku.

Innym zastosowaniem wątków jest po prostu możliwość lepszej reakcji programu. Jeśli tworzysz dużą aplikacji lub gdy użytkownik naciśnie przycisk aplikacji rozpoczynając jakiś duży proces ... dopóki trwa przetwarzanie, ekran przestaje odpowiadać, co powoduje błędne lub mylące wrażenie, że aplikacja jest zawieszona. Jeśli duży proces przebiega w drugim wątku, aplikacja zachowuje się (prawie) tak, jakby była w stanie bezczynności. W tym przypadku dobrym pomysłem jest aby, przed rozpoczęciem wątku, wyłączyć odpowiednie przyciski na formularzu, w celu uniknięcia ponownego uruchomienia drugiego wątku przez użytkownika.

Jeszcze innym zastosowaniem wielowątkowości może być serwer, który jest w stanie dać odpowiedź wielu klientom, w tym samym czasie.

Czy potrzebujesz wielowątkowości?

Jeśli dopiero poznajesz wielowątkowość i chciałbyś tylko stworzyć aplikację z szybszym czasem reakcji w chwili gdy wykonuje ona umiarkowanie długotrwałe zadanie, wówczas wielowątkowość może być więcej niż wskazana. Aplikacje wielowątkowe zawsze są trudniejsze do debugowania i często są one o wiele bardziej skomplikowane, jednak w wielu przypadkach wcale nie trzeba używać wielowątkowości. Jeden wątek jest wystarczający. Jeśli możesz podzielić czasochłonne zadanie na kilka mniejszych kawałków, należy użyć procedurę Application.ProcessMessages. Procedura ta pozwala bibliotece LCL obsłużyć wszystkie oczekujące wiadomości i powrócić do jej wywołania. Główną ideą jest to, aby wywoływać Application.ProcessMessages w regularnych odstępach czasu w trakcie wykonywania długotrwałego zadania, np. po to aby sprawdzić, czy może użytkownik kliknął na jakiejś kontrolce albo może wskaźnik postępu musi być przemalowany albo zdarzyło się jeszcze coś innego.

Przykład: Czytanie dużego pliku i jego przetwarzanie. Zobacz: examples/multithreading/singlethreadingexample1.lpi.

Wielowątkowość jest potrzebna tylko dla

  • uchwytów blokujących, takich jak w komunikacji sieci
  • korzystania z wielu procesorów jednocześnie (SMP)
  • algorytmów i podłączania bibliotek, które muszą być wywoływane przez API i jako takie nie mogą być podzielone na mniejsze części.

Jeżeli chcesz użyć wielowątkowości, aby zwiększyć prędkość przy użyciu wielu procesorów jednocześnie, sprawdź, czy twój obecny program w tej chwili wykorzystuje 100% zasobów 1 rdzenia CPU (na przykład, program może aktywnie korzystać z operacji wejścia-wyjścia, jak zapis do pliku i to zajmuje dużo czasu, ale nie obciąża procesora, i w tym przypadku program nie będzie działał szybciej z wieloma wątkami). Należy również sprawdzić, czy poziom optymalizacji jest ustawiony na maksymalny (3). Kiedy zmieniłem optymalizację z poziomu 1 na 3, mój program zaczął działać około 5 razy szybciej.

Moduły potrzebne do tworzenia aplikacji wielowątkowych

Nie potrzebujesz żadnych specjalnych modułów do tego, aby pracować z systemem Windows. Jednak z systemem Linux, Mac OS X i FreeBSD, należy użyć modułu cthreads i musi być on użyty jako pierwszy moduł projektu (program źródłowy, zwykle znajdujący się w pliku .lpr)!

Dlatego twój kod aplikacji Lazarusa powinien wyglądać tak:

program MyMultiThreadedProgram;
{$mode objfpc}{$H+}
uses
{$ifdef unix}
  cthreads,
  cmem, // menedżer pamięci c jest w niektórych systemach znacznie szybszy dla aplikacji wielowątkowych
{$endif}
  Interfaces, // to zawiera widżety LCL
  Forms
  { tu możesz dodać następne moduły },

Jeśli zapomnisz o tym i użyjesz TThread, otrzymasz następujący błąd podczas uruchamiania:

 This binary has no thread support compiled in.
 Recompile the application with a thread-driver in the program uses clause before other units using thread.
Note-icon.png

Uwaga: Jeśli pojawi się błąd linkera o tym, że nie znaleziono "mcount" to znaczy, że używasz jakiegoś modułu, który zawiera kod wielowątkowy i musisz dodać moduł cthreads lub użyć sprytnego łączenia.

Note-icon.png

Uwaga: Jeśli otzrymasz błąd: "Project raised exception class 'RunError(232)'" w procedurze SYSTEM_NOTHREADERROR to znaczy, że twój kod potrzebuje wątków i musisz dodał moduł cthreads.

Klasa TThread

The following example can be found in the examples/multithreading/ directory.

To create a multi-threaded application, the easiest way is to use the TThread Class. This class permits the creation of an additional thread (alongside the main thread) in a simple way. Normally you are required to override only 2 methods: the Create constructor, and the Execute method.

In the constructor, you will prepare the thread to run. You will set the initial values of the variables or properties you need. The original constructor of TThread requires a parameter called Suspended. As you might expect, setting Suspended = True will prevent the thread starting automatically after the creation. If Suspended = False, the thread will start running just after the creation. If the thread is created suspended, then it will run only after the Start method is called.

Note-icon.png

Note: Method Resume is deprecated since FPC 2.4.4. It is replaced by Start.

As of FPC version 2.0.1 and later, TThread.Create also has an implicit parameter for Stack Size. You can now change the default stack size of each thread you create if you need it. Deep procedure call recursions in a thread are a good example. If you don't specify the stack size parameter, a default OS stack size is used.

In the overridden Execute method you will write the code that will run on the thread.

The TThread class has one important property: Terminated : boolean;

If the thread has a loop (and this is typical), the loop should be exited when Terminated is true (it is false by default). Within each pass, the value of Terminated must be checked, and if it is true then the loop should be exited as quickly as is appropriate, after any necessary cleanup. Bear in mind that the Terminate method does not do anything by default: the .Execute method must explicitly implement support for it to quit its job.

As we explained earlier, the thread should not interact with the visible components. Updates to visible components must be made within the context of the main thread.

To do this, a TThread method called Synchronize exists. Synchronize requires a method within the thread (that takes no parameters) as an argument. When you call that method through Synchronize(@MyMethod), the thread execution will be paused, the code of MyMethod will be called from the main thread, and then the thread execution will be resumed.

The exact working of Synchronize depends on the platform, but basically it does this:

  • it posts a message onto the main message queue and goes to sleep
  • eventually the main thread processes the message and calls MyMethod. This way MyMethod is called without context, that means not during a mouse down event or during paint event, but after.
  • after the main thread executed MyMethod, it wakes the sleeping Thread and processes the next message
  • the Thread then continues.

There is another important property of TThread: FreeOnTerminate. If this property is true, the thread object is automatically freed when the thread execution (.Execute method) stops. Otherwise the application will need to free it manually.

Example:

  Type
    TMyThread = class(TThread)
    private
      fStatusText : string;
      procedure ShowStatus;
    protected
      procedure Execute; override;
    public
      Constructor Create(CreateSuspended : boolean);
    end;
 
  constructor TMyThread.Create(CreateSuspended : boolean);
  begin
    FreeOnTerminate := True;
    inherited Create(CreateSuspended);
  end;
 
  procedure TMyThread.ShowStatus;
  // this method is executed by the mainthread and can therefore access all GUI elements.
  begin
    Form1.Caption := fStatusText;
  end;
 
  procedure TMyThread.Execute;
  var
    newStatus : string;
  begin
    fStatusText := 'TMyThread Starting...';
    Synchronize(@Showstatus);
    fStatusText := 'TMyThread Running...';
    while (not Terminated) and ([any condition required]) do
      begin
        ...
        [here goes the code of the main thread loop]
        ...
        if NewStatus <> fStatusText then
          begin
            fStatusText := newStatus;
            Synchronize(@Showstatus);
          end;
      end;
  end;

On the application,

  var
    MyThread : TMyThread;
  begin
    MyThread := TMyThread.Create(True); // This way it doesn't start automatically
    ...
    [Here the code initialises anything required before the threads starts executing]
    ...
    MyThread.Start;
  end;

If you want to make your application more flexible you can create an event for the thread; this way your synchronized method won't be tightly coupled with a specific form or class: you can attach listeners to the thread's event. Here is an example:

  Type
    TShowStatusEvent = procedure(Status: String) of Object;
 
    TMyThread = class(TThread)
    private
      fStatusText : string;
      FOnShowStatus: TShowStatusEvent;
      procedure ShowStatus;
    protected
      procedure Execute; override;
    public
      Constructor Create(CreateSuspended : boolean);
      property OnShowStatus: TShowStatusEvent read FOnShowStatus write FOnShowStatus;
    end;
 
  constructor TMyThread.Create(CreateSuspended : boolean);
  begin
    FreeOnTerminate := True;
    inherited Create(CreateSuspended);
  end;
 
  procedure TMyThread.ShowStatus;
  // this method is executed by the mainthread and can therefore access all GUI elements.
  begin
    if Assigned(FOnShowStatus) then
    begin
      FOnShowStatus(fStatusText);
    end;
  end;
 
  procedure TMyThread.Execute;
  var
    newStatus : string;
  begin
    fStatusText := 'TMyThread Starting...';
    Synchronize(@Showstatus);
    fStatusText := 'TMyThread Running...';
    while (not Terminated) and ([any condition required]) do
      begin
        ...
        [here goes the code of the main thread loop]
        ...
        if NewStatus <> fStatusText then
          begin
            fStatusText := newStatus;
            Synchronize(@Showstatus);
          end;
      end;
  end;

On the application,

  Type
    TForm1 = class(TForm)
      Button1: TButton;
      Label1: TLabel;
      procedure FormCreate(Sender: TObject);
      procedure FormDestroy(Sender: TObject);
    private
      { private declarations }
      MyThread: TMyThread; 
      procedure ShowStatus(Status: string);
    public
      { public declarations }
    end;
 
  procedure TForm1.FormCreate(Sender: TObject);
  begin
    inherited;
    MyThread := TMyThread.Create(true);
    MyThread.OnShowStatus := @ShowStatus;
  end;
 
  procedure TForm1.FormDestroy(Sender: TObject);
  begin
    MyThread.Terminate;
 
    // FreeOnTerminate is true so we should not write:
    // MyThread.Free;
    inherited;
  end;
 
  procedure TForm1.Button1Click(Sender: TObject);
  begin
   MyThread.Start;
  end;
 
  procedure TForm1.ShowStatus(Status: string);
  begin
    Label1.Caption := Status;
  end;

Ważne rzeczy, na które trzeba zwrócić uwagę

Kontrola stosu w systemie Windows

There is a potential headache in Windows with Threads if you use the -Ct (stack check) switch. For reasons not so clear the stack check will "trigger" on any TThread.Create if you use the default stack size. The only work-around for the moment is to simply not use -Ct switch. Note that it does NOT cause an exception in the main thread, but in the newly created one. This "looks" like if the thread was never started.

A good code to check for this and other exceptions which can occur in thread creation is:

MyThread := TThread.Create(False);
if Assigned(MyThread.FatalException) then
  raise MyThread.FatalException;

This code will assure that any exception which occurred during thread creation will be raised in your main thread.

Wielowątkowość w pakietach

Packages which uses multi-threading should add the -dUseCThreads flag to the custom usage options. Open the package editor of the package, then Options > Usage > Custom and add -dUseCThreads. This will define this flag to all projects and packages using this package, including the IDE. The IDE and all new applications created by the IDE have already the following code in their .lpr file:

uses
  {$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  cmem, // the c memory manager is on some systems much faster for multi-threading
  {$ENDIF}{$ENDIF}

Moduł Heaptrc

You can not use the -gh switch with the cmem unit. The -gh switch uses the heaptrc unit, which extends the heap manager. Therefore the heaptrc unit must be used after the cmem unit.

uses
  {$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  cmem, // the c memory manager is on some systems much faster for multi-threading
  {$ENDIF}{$ENDIF}
  heaptrc,

Wsparcie dla SMP

The good news is that if your application works properly multi-threaded this way, it is already SMP enabled!

Debugowanie aplikacji wielowątkowych w Lazarusie

The debugging on Lazarus requires GDB and is rapidly becoming more and more fully featured and stable. However, there still exists a few Linux distributions with some problems.

Wyjście debuggera

In a single threaded application, you can simply write to console/terminal/whatever and the order of the lines is the same as they were written. In multi-threaded application things are more complicated. If two threads are writing, say a line is written by thread A before a line by thread B, then the lines are not necessarily written in that order. It can even happen, that a thread writes its output, while the other thread is writing a line.While under linux (maybe) you'll get proper DebugLn() output, under win32 you can get exceptions (probably DiskFull) because of DebugLn() usage outside of main thread.So, to avoid headaches use DebugLnThreadLog() mentioned below.

The LCLProc unit contains several functions, to let each thread write to its own log file:

  procedure DbgOutThreadLog(const Msg: string); overload;
  procedure DebuglnThreadLog(const Msg: string); overload;
  procedure DebuglnThreadLog(Args: array of const); overload;
  procedure DebuglnThreadLog; overload;

For example: Instead of writeln('Some text ',123); use

 DebuglnThreadLog(['Some text ',123]);

This will append a line 'Some text 123' to Log<PID>.txt, where <PID> is the process ID of the current thread.

It is a good idea to remove the log files before each run:

 rm -f Log* && ./project1

Linux

If you try to debug a multi-threaded application on Linux, you will have one big problem: the Desktop Manager on X server can hang. This happens for instance when the application has captured the mouse/keyboard and was paused by gdb and the X server waits for your application. When that happens you can simply log in from another computer and kill the gdb or exit out of that session by pressing CTRL+ALT+F3 and kill gdb. Alternatively you can restart the window manager: enter sudo /etc/init.d/gdm restart. This will restart the desktop manager and get you back into your desktop.

Since it depends where gdb stops your program in some cases some tricks may help: for Ubuntu x64 set the Project options for debugging required extra information file...

 Project Options -> Compiler Options -> Linking -> Debugging: Check Use external gdb debug symbols file (-Xg).

The other option is to open anotner X desktop, run the IDE/gdb on one and the application on the other, so that only the test desktop freezes. Create a new instance of X with:

 X :1 &

It will open, and when you switch to another desktop (the one you are working with pressing CTRL+ALT+F7), you will be able to go back to the new graphical desktop with CTRL+ALT+F8 (if this combination does not work, try with CTRL+ALT+F2... this one worked on Slackware).

Then you could, if you want, create a desktop session on the X started with:

 gnome-session --display=:1 &

Then, in Lazarus, on the run parameters dialog for the project, check "Use display" and enter :1.

Now the application will run on the second X server and you will be able to debug it on the first one.

This was tested with Free Pascal 2.0 and Lazarus 0.9.10 on Windows and Linux.



Instead of creating a new X session, one can use Xnest. Xnest is a X session on a window. Using it X server didn't lock while debugging threads, and it's much easier to debug without keeping changing terminals.

The command line to run Xnest is

 Xnest :1 -ac

to create a X session on :1, and disabling access control.

Modyfikowanie widżetów (in. kontrolek, formatek) interfejsu w Lazarusie

The win32, the gtk and the carbon interfaces support multi-threading. This means, TThread, critical sections and Synchronize work. But they are not thread safe. This means only one thread at a time can access the LCL. And since the main thread should never wait for another thread, it means only the main thread is allowed to access the LCL, which means anything that has to do with TControl, Application and LCL widget handles. There are some thread safe functions in the LCL. For example most of the functions in the FileUtil unit are thread safe.

Użycie SendMessage/PostMessage do komunikacji pomiędzy wątkami

Only one thread in an application should call LCL APIs, usually the main thread. Other threads can make use of the LCL through a number of indirect methods, one good option being the usage of SendMessage or PostMessage. LCLIntf.SendMessage and LCLIntf.PostMessage will post a message directed to a window in the message pool of the application.

See also the documentation for these routines:

The difference between SendMessage and PostMessage is the way that they return control to the calling thread. With SendMessage control is not returned until the window that the message was sent to has completed processing the sent message, however with PostMessage control is returned immediately.

Here is an example of how a secondary thread could send text to be displayed in an LCL control to the main thread:

const
  WM_GOT_ERROR           = LM_USER + 2004;
  WM_VERBOSE             = LM_USER + 2005;
 
procedure VerboseLog(Msg: string);
var
  PError: PChar;
begin
  if MessageHandler = 0 then Exit;
  PError := StrAlloc(Length(Msg)+1);
  StrCopy(PError, PChar(Msg));
  PostMessage(formConsole.Handle, WM_VERBOSE, Integer(PError), 0);
end;

And an example of how to handle this message from a window:

const
  WM_GOT_ERROR           = LM_USER + 2004;
  WM_VERBOSE             = LM_USER + 2005;
 
type
  { TformConsole }
 
  TformConsole = class(TForm)
    DebugList: TListView;
    // ...
  private
    procedure HandleDebug(var Msg: TLMessage); message WM_VERBOSE;
  end;
 
var
  formConsole: TformConsole;
 
implementation
 
....
 
{ TformConsole }
 
procedure TformConsole.HandleDebug(var Msg: TLMessage);
var
  Item: TListItem;
  MsgStr: PChar;
  MsgPasStr: string;
begin
  MsgStr := PChar(Msg.wparam);
  MsgPasStr := StrPas(MsgStr);
  Item := DebugList.Items.Add;
  Item.Caption := TimeToStr(SysUtils.Now);
  Item.SubItems.Add(MsgPasStr);
  Item.MakeVisible(False);
  //f/TrayControl.SetError(MsgPasStr);
end;
 
end.

Sekcje krytyczne

A critical section is an object used to make sure, that some part of the code is executed only by one thread at a time. A critical section needs to be created/initialized before it can be used and be freed when it is not needed anymore.

Critical sections are normally used this way:

Declare the section (globally for all threads which should access the section):

 MyCriticalSection: TRTLCriticalSection;

Create the section:

 InitializeCriticalSection(MyCriticalSection);

Run some threads. Doing something exclusively

EnterCriticalSection(MyCriticalSection);
try
  // access some variables, write files, send some network packets, etc
finally
  LeaveCriticalSection(MyCriticalSection);
end;

After all threads terminated, free it:

 DeleteCriticalSection(MyCriticalSection);

As an alternative, you can use a TCriticalSection object. The creation does the initialization, the Enter method does the EnterCriticalSection, the Leave method does the LeaveCriticalSection and the destruction of the object does the deletion.

For example: 5 threads incrementing a counter. See lazarus/examples/multithreading/criticalsectionexample1.lpi

BEWARE: There are two sets of the above 4 functions. The RTL and the LCL ones. The LCL ones are defined in the unit LCLIntf and LCLType. Both work pretty much the same. You can use both at the same time in your application, but you should not use a RTL function with an LCL Critical Section and vice versus.


Współdzielenie zmiennych

If some threads share a variable, that is read only, then there is nothing to worry about. Just read it. But if one or several threads changes the variable, then you must make sure, that only one thread accesses the variables at a time.

For example: 5 threads incrementing a counter. See lazarus/examples/multithreading/criticalsectionexample1.lpi

Oczekiwanie na inny wątek

If a thread A needs a result of another thread B, it must wait, till B has finished.

Important: The main thread should never wait for another thread. Instead use Synchronize (see above).

See for an example: lazarus/examples/multithreading/waitforexample1.lpi

{ TThreadA }
 
procedure TThreadA.Execute;
begin
  Form1.ThreadB:=TThreadB.Create(false);
  // create event
  WaitForB:=RTLEventCreate;
  while not Application.Terminated do begin
    // wait infinitely (until B wakes A)
    RtlEventWaitFor(WaitForB);
    writeln('A: ThreadB.Counter='+IntToStr(Form1.ThreadB.Counter));
  end;
end;
 
{ TThreadB }
 
procedure TThreadB.Execute;
var
  i: Integer;
begin
  Counter:=0;
  while not Application.Terminated do begin
    // B: Working ...
    Sleep(1500);
    inc(Counter);
    // wake A
    RtlEventSetEvent(Form1.ThreadA.WaitForB);
  end;
end;
Note-icon.png

Note: RtlEventSetEvent can be called before RtlEventWaitFor. Then RtlEventWaitFor will return immediately. Use RTLeventResetEvent to clear a flag.

Wątek potomny (fork)

When forking in a multi-threaded application, be aware that any threads created and running BEFORE the fork (or fpFork) call, will NOT be running in the child process. As stated on the fork() man page, any threads that were running before the fork call, their state will be undefined.

So be aware of any threads initializing before the call (including on the initialization section). They will NOT work.

Procedury/pętle równoległe

A special case of multi threading is running a single procedure in parallel. See Parallel procedures.

Obliczenia rozproszone

The next higher steps after multi threading is running the threads on multiple machines.

  • You can use one of the TCP suites like synapse, lnet or indy for communications. This gives you maximum flexibility and is mostly used for loosely connected Client / Server applications.
  • You can use message passing libraries like MPICH, which are used for HPC (High Performance Computing) on clusters.


Wątki zewnętrzne

To make Free Pascal's threading system work properly, each newly created FPC thread needs to be initialized (more exactly, the exception, I/O system and threadvar system per thread needs to be initialized so threadvars and heap are working). That is fully automatically done for you if you use BeginThread (or indirectly by using the TThread class). However, if you use threads that were created without BeginThread (i.e. external threads), additional work (currently) might be required. External threads also include those that were created in external C libraries (.DLL/.so).


Things to consider when using external threads (might not be needed in all or future compiler versions):

  • Do not use external threads at all - use FPC threads. If can you can get control over how the thread is created, create the thread by yourself by using BeginThread.

If the calling convention doesn't fit (e.g. if your original thread function needs cdecl calling convention but BeginThread needs pascal convention, create a record, store the original required thread function in it, and call that function in your pascal thread function:

type
 TCdeclThreadFunc = function (user_data:Pointer):Pointer;cdecl;
 
 PCdeclThreadFuncData = ^TCdeclThreadFuncData;
 TCdeclThreadFuncData = record
   Func: TCdeclThreadFunc;  //cdecl function
   Data: Pointer;           //original data
 end;
 
// The Pascal thread calls the cdecl function
function C2P_Translator(FuncData: pointer) : ptrint;
var
  ThreadData: TCdeclThreadFuncData;
begin
  ThreadData := PCdeclThreadFuncData(FuncData)^;
  Result := ptrint(ThreadData.Func(ThreadData.Data));
end;
 
procedure CreatePascalThread;
var
  ThreadData: PCdeclThreadFuncData;
begin
  New(ThreadData);
  // this is the desired cdecl thread function
  ThreadData^.Func := func;
  ThreadData^.Data := user_data;
  // this creates the Pascal thread
  BeginThread(@C2P_Translator, ThreadData );
end;


  • Initialize the FPC's threading system by creating a dummy thread. If you don't create any Pascal thread in your app, the thread system won't be initialized (and thus threadvars won't work and thus heap will not work correctly).
type
   tc = class(tthread)
     procedure execute;override;
   end;
 
   procedure tc.execute;
   begin
   end;
 
{ main program } 
begin
  { initialise threading system }
   with tc.create(false) do
   begin
     waitfor;
     free;
   end;
   { ... your code follows } 
end.

(After the threading system is initialized, the runtime may set the system variable "IsMultiThread" to true which is used by FPC routines to perform locks here and there. You should not set this variable manually.)


  • If for some reason this doesn't work for you, try this code in your external thread function:
function ExternalThread(param: Pointer): LongInt; stdcall;
var
  tm: TThreadManager;
begin
  GetThreadManager(tm);
  tm.AllocateThreadVars;
  InitThread(1000000); // adjust inital stack size here
 
  { do something threaded here ... }
 
  Result:=0;
end;


Identyfikacja zewnętrznych wątków

Sometimes you even don't know if you have to deal with external threads (e.g. if some C library makes a callback). This can help to analyse this:

1. Ask the OS for the ID of the current thread at your application's start

Win32: GetCurrentThreadID();
Darwin: GetThreadID();  
Linux: TThreadID(pthread_self);

2. Ask again for the ID of the current thread inside the thread function and compare this by the result of step 1.

Rezygnacja z opóźnień czasowych

ThreadSwitch()

Note-icon.png

Note: Nie używaj sztuczki z uśpieniem w Windows Sleep(0) ponieważ nie będzie to działać na wszystkich platformach.

Zobacz także