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I'mSRJ's questions

Martin Hope
I'mSRJ
Asked: 2024-12-31 02:10:21 +0800 CST
  • 6

我已经使用 Delphi 有一段时间了，现在正尝试在我的代码中实现多线程，要求如下：

  1. 每次只能运行 2 个线程。

  2. 其他任务应在队列中等待，并在线程可用时执行。

我尝试使用TParallel.For来实现这一点，但无法实现所需的行为。这是我的示例代码：

    type
       TMyRecord = record
         msg: String;
         sleep: Integer;
          end;

    var
      Form2: TForm2;

    implementation

    {$R *.dfm}

    procedure TForm2.Button1Click(Sender: TObject);
    var
      record1, record2, record3, record4, record5: TMyRecord;
      MyList: TList<TMyRecord>;
    begin
      // Initialize records
      record1.msg := 'Item1';
      record1.sleep := 10;

      record2.msg := 'Item2';
      record2.sleep := 10;

      record3.msg := 'Item3';
      record3.sleep := 3000;

      record4.msg := 'Item4';
      record4.sleep := 3000;

      record5.msg := 'Item5';
      record5.sleep := 100;

     MyList := TList<TMyRecord>.Create;
      try
        // Add records to the list
        MyList.Add(record1);
        MyList.Add(record2);
        MyList.Add(record3);
        MyList.Add(record4);
        MyList.Add(record5);

    // Use TParallel.For
    TParallel.For(0, MyList.Count - 1,
      procedure (i: Integer)
      var
        ListItem: TMyRecord;
      begin
        ListItem := MyList[i];

        TThread.Synchronize(nil,
          procedure
          begin
            Memo1.Lines.Add(ListItem.msg);
          end);

        Sleep(ListItem.sleep);
      end);

      finally
    MyList.Free;
  end;
end;

我也尝试使用TTask.Run和ThreadPool，但无法实现所需的行为。更新 - 这是我尝试使用 Threadpool 执行的操作

procedure TForm2.Button1Click(Sender: TObject);
var
  record1, record2, record3, record4, record5: TMyRecord;
  MyList: TList<TMyRecord>;
  ThreadPool: TThreadPool;
begin
  // Initialize records
  record1.msg := 'Item1';
  record1.sleep := 10;

  record2.msg := 'Item2';
  record2.sleep := 10;

  record3.msg := 'Item3';
  record3.sleep := 3000;

  record4.msg := 'Item4';
  record4.sleep := 3000;

  record5.msg := 'Item5';
  record5.sleep := 100;

  MyList := TList<TMyRecord>.Create;
  try
    // Add records to the list
    MyList.Add(record1);
    MyList.Add(record2);
    MyList.Add(record3);
    MyList.Add(record4);
    MyList.Add(record5);

    ThreadPool := TThreadPool.Create;
    ThreadPool.SetMaxWorkerThreads(2);

    // Iterate through the list and queue each work item with a copy of the record
    for var i := 0 to MyList.Count - 1 do
    begin
      var ListItem := MyList[i];

      ThreadPool.QueueWorkItem(
        procedure
        var
          LocalItem: TMyRecord;
        begin
          LocalItem := ListItem;

          TThread.Queue(nil,
            procedure
            begin
              Memo1.Lines.Add(LocalItem.msg);
              Sleep(LocalItem.sleep);  // Simulate the delay
            end);
        end);
    end;
  finally
    MyList.Free;
  end;
end;

此代码有问题-

  1. 它仅打印“item5”5次。
  2. 等待时间（睡眠）不起作用。

我该如何修改此代码以将同时运行的线程数限制为 2？并在线程可用时将其他任务排队执行？

multithreading