SendMessage to window created by AllocateHWND cause deadlock
- by user2704265
In my Delphi project, I derive a thread class TMyThread, and follow the advice from forums to use AllocateHWnd to create a window handle. In TMyThread object, I call SendMessage to send message to the window handle.
When the messages sent are in small volume, then the application works well. However, when the messages are in large volume, the application will deadlock and lose responses. I think may be the message queue is full as in LogWndProc, there are only codes to process the message, but no codes to remove the messages from the queue, that may cause all the processed messages still exist in the queue and the queue becomes full. Is that correct?
The codes are attached below:
var
hLogWnd: HWND = 0;
procedure TForm1.FormCreate(Sender: TObject);
begin
hLogWnd := AllocateHWnd(LogWndProc);
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
if hLogWnd <> 0 then
DeallocateHWnd(hLogWnd);
end;
procedure TForm1.LogWndProc(var Message: TMessage);
var
S: PString;
begin
if Message.Msg = WM_UPDATEDATA then
begin
S := PString(msg.LParam);
try
List1.Items.Add(S^);
finally
Dispose(S);
end;
end else
Message.Result := DefWindowProc(hLogWnd, Message.Msg, Message.WParam,
Message.LParam);
end;
procedure TMyThread.SendLog(I: Integer);
var
Log: PString;
begin
New(Log);
Log^ := 'Log: current stag is ' + IntToStr(I);
SendMessage(hLogWnd, WM_UPDATEDATA, 0, LPARAM(Log));
Dispose(Log);
end;
