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Shweta Softwares
Asked: 2025-01-02 00:16:44 +0800 CST

如何在 Delphi 中使用 TTask 和 TThreadPool 运行多个任务并确保准确报告其启动和完成情况？

  • 772

我正在尝试在 Delphi 10.4 (Sydney) 中实现多线程。我使用 TTask 并发运行任务，使用 TThreadPool 限制同时运行的线程。

这是我的代码：

var
  MyThreadPool: TThreadPool;
  I: Integer;
  Tasks: TArray<ITask>;

function ProcessTask(const TaskId: Integer): TProc;
begin
  Result := procedure
  Begin
    WriteLn(Format('Started TaskId: %d ThreadId: %d',[TaskId,TThread.Current.ThreadID]));
    Sleep(2000); // Simulate work
    WriteLn(format('TaskId %d completed. ThreadId: %d',[TaskId, TThread.Current.ThreadID]));
  End;
end;

begin
  try

    Writeln('Creating TThreadPool');
    MyThreadPool := TThreadPool.Create;

    try
      MyThreadPool.SetMinWorkerThreads(1);
      MyThreadPool.SetMaxWorkerThreads(4);

      // Hold 10 tasks
      SetLength(Tasks,10);

      for I := 0 to High(Tasks) do
      Begin
        Tasks[I] := TTask.Create(
          ProcessTask(I+1),
          MyThreadPool
        );

        // Start the task
        Tasks[I].Start;
      End;

      // Wait for all tasks to complete
      for I := 0 to High(Tasks) do
        Tasks[I].Wait;

      WriteLn('All tasks completed.');
      ReadLn;

    finally
      MyThreadPool.Free;
    end;

  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

上述代码的输出是：

Creating TThreadPool
Started TaskId: 1 ThreadId: 17292
Started TaskId: 1 ThreadId: 17292
Started TaskId: 2 ThreadId: 19256
Started TaskId: 3 ThreadId: 25268
Started TaskId: 3 ThreadId: 25268
Started TaskId: 4 ThreadId: 21112
TaskId 1 completed. ThreadId: 17292
Started TaskId: 5 ThreadId: 17292
TaskId 2 completed. ThreadId: 19256
Started TaskId: 6 ThreadId: 19256
TaskId 3 completed. ThreadId: 25268
TaskId 3 completed. ThreadId: 25268
TaskId 4 completed. ThreadId: 21112
Started TaskId: 7 ThreadId: 21112Started TaskId: 8 ThreadId: 25268Started TaskId: 7 ThreadId: 21112Started TaskId: 8 ThreadId: 25268
TaskId 5 completed. ThreadId: 17292
Started TaskId: 9 ThreadId: 17292
TaskId 6 completed. ThreadId: 19256
Started TaskId: 10 ThreadId: 19256
TaskId 8 completed. ThreadId: 25268
TaskId 8 completed. ThreadId: 25268
TaskId 7 completed. ThreadId: 21112
TaskId 9 completed. ThreadId: 17292
TaskId 10 completed. ThreadId: 19256
All tasks completed.

代码的问题在于在某些情况下开始和完成报告会重复：

  1. Started TaskId出现了两次，分别为 TaskId 1,3,7,8。
  2. TaskId完成出现了两次，分别是 TaskId 3,8。
multithreading

1 个回答

  1. Best Answer

    无需深入研究，问题很可能在于您使用的WriteLn是容易出现问题的多线程代码。在输出中添加某种同步，以确保WriteLn一次只执行一个调用。

    var
  ConsoleLock: TCriticalSection;

procedure SafeWriteLn(const Msg: string);
begin
  ConsoleLock.Enter;
  try
    WriteLn(Msg);
  finally
    ConsoleLock.Leave;
  end;
end;

ConsoleLock := TCriticalSection.Create;
try
  //your stuff
finally
  ConsoleLock.Free;
end;
    • 5

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