多线程Delphi Stop

Question

I have a frame, inside it I have a thread, the creation of this front and at runtime, each click that give the button it creates a new frame and may have innumerable within the form. the problem is that ... I create the first, the thread starts normal when I create the second, the first thread to, and the second begins, if I click again, the first and second stand still and the third begins, if I close the third, the second back to work, because this happens? thank you

constructor TMy_Thread.Create(fraConnect : TfraConnect);
begin
  inherited Create(True);
  Priority        := tpTimeCritical;
  FreeOnTerminate := true;
  fraConnectT     := fraConnect;
end;

procedure TMy_Thread.Execute;
begin
  Synchronize(Teste);
end;

procedure TMy_Thread.TEste;
var
  iSize : Int64;
  iCnt  : Integer;
  Msg : TMsg ;
begin
  inherited;
  with fraConnectT do begin
    While not Terminated do begin
      Log(fraConnectT.Name,'');
      Application.ProcessMessages;
    end;
  end;
end;


////////////////

procedure TfraConnect.Click(Sender: TObject);
var
  Sc : TMy_Thread;
begin
  Sc                    := TMy_Thread.Create(Self);
  try
    iTela            := 0;
    Sc.Execute;
  finally
    Sc.Terminate;
  end;
end;

Answer 1

You are not using TThread correctly. You are not starting the thread (so it does not free itself when terminated), you are calling Execute() directly, you are Synchronize ing the entire body of Execute() . So Execute() runs in the main thread, calling ProcessMessages() to allow a new button click, which calls Execute() blocking the previous Execute() until the new Execute() exits, and so on. That is why you are experiencing the symptoms you are seeing.

To fix this, you need to do the following:

• In the thread constructor, call inherited Create(False) instead. This allows the thread to start running automatically. Otherwise, you have to call the thread's Resume() or Start() method after the constructor exits.

• remove Execute() from Click() . Let the running thread call Execute() .

• remove ProcessMessages() from Teste() . There is never a need to call ProcessMessages() in a thread (unless it is being called inside of Synchronize d or Queue d code running in the main thread, but even then it should be avoided when possible).

• only Synchronize() small code blocks that actually need to run in the main thread - code that does not work in a secondary thread, code that needs to access the UI, code that needs to access a resource shared by multiple threads, etc. The bulk of your thread code should NOT be Synchronize d, that defeats the purpose of using a thread in the first place.

Try something more like this:

type
  fraConnect = class;
  TMy_Thread = class(TThread)
  private
    fraConnectT : TfraConnect;
    procedure DoLog;
  protected
    procedure Execute; override;
  public
    constructor Create(fraConnect : TfraConnect);
    property Terminated;
  end;

...

constructor TMy_Thread.Create(fraConnect : TfraConnect);
begin
  inherited Create(True);
  Priority        := tpTimeCritical;
  FreeOnTerminate := true;
  fraConnectT     := fraConnect;
end;

procedure TMy_Thread.Execute;
begin
  with fraConnectT do begin
    While not Terminated do begin
      // assuming Log() is not thread-safe...
      Synchronize(DoLog);
      Sleep(100);
    end;
  end;
end;

procedure TMy_Thread.DoLog;
begin
  Log(fraConnectT.Name,'');
end;

type
  TMy_Thread = class;
  TfraConnect = class(TFrame)
    Start: TButton;
    Stop: TButton;
    StartClick(Sender: TObject);
    StopClick(Sender: TObject);
  private
    Sc: TMy_Thread;
    procedure ThreadTerminated(Sender: TObject);
  end;

...

procedure TfraConnect.StartClick(Sender: TObject);
begin
  if (not Assigned(Sc)) or Sc.Terminated then
  begin
    Sc := TMy_Thread.Create(Self);
    Sc.OnTerminate := ThreadTerminated;
    Sc.Resume; // or Sc.Start;
  end;
end;

procedure TfraConnect.StopClick(Sender: TObject);
begin
  if Assigned(Sc) then
    Sc.Terminate;
end;

procedure TfraConnect.ThreadTerminated(Sender: TObject);
begin
  if Sc = Sender then
    Sc := nil;
end;