Multiple TThread Instances

Question

I have a TThread Class that can run independently and terminates and frees itself after it's done. I considered the termination and everything works. The problem is, that I would like to add a feature that the user can select and choose how many SYNCHRONOUS threads should be active at the same time. An example would be:

• The program has to do 100 total tasks!
• The user chooses 3 Threads should be running at the same time to complete all the tasks.

The first step I did was to create 3 instances of my TThread Class and the resume them in a for loop. So 3 threads are running. After the first thread is done (or terminated), another new instance needs to be created and resumed.

I get stuck on this point and I wonder how I can realize this. Any advice would be helpful.

Edit: Some Code

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

type
  TMyThread = class (TThread)
  public
  procedure Execute; override;
end;

var
  Form1       : TForm1;
  Threads     : Integer = 3;
  TotalTasks  : Integer = 100;

implementation

{$R *.dfm}

procedure TMyThread.Execute;
begin
  // some work...
  sleep (2000 + random (5000));
end;

function DummyThread ( p : pointer ) : Integer; stdcall;
var
  NewInstanceOfTMyThread  : TMyThread;
  I                       : Integer;
begin
  for I := 1 to Threads do begin
    with TMyThread.Create (TRUE) do begin
      resume;
    end;
  end;
  // Here should be code to detect if a new thread has to be started, etc.
end;

// We start the task to start the tasks...
procedure TForm1.Button1Click(Sender: TObject);
var
  ThreadID    : DWORD;
begin
  CloseHandle (CreateThread(NIL, 0, @DummyThread, NIL, 0, ThreadID));
end;

end.

Answer 1

You can write a handler for OnTerminate event of TThread. The handler should start/resume a new thread.

Or you can have 3 threads which are running constantly and take tasks from some queue (just take care of synchronizing the queue access).