Question

OK I’m writing a Zoom component and I wanted it to capture from screen within a secondary thread.
You can pretend I just want to derive TThread in an empty component. I didn’t write any codes in the thread so it is just a simple useless thread. I wrote this code: Thrd := TCaptureThread.Create(False); in the component main class.
Then I wrote Thrd.Free in the main class destruction code. Now when I close the whole application, although it destroys everything, the process doesn’t terminate completely. In Windows Task Manager shows that number of threads is 1 but the process remains. If I comment the thread creation line, everything becomes OK and application terminates quickly. What am I gonna do about this? 🙁

Thanks in advance

Answer 1

When you call Thrd.Free the following code from TThread.Destroy is run:

Terminate;
if FCreateSuspended then
  Resume;
WaitFor;

Calling Free on a thread will thus terminate the thread synchronously.

My guess is that the call to WaitFor never returns. Perhaps TCaptureThread.Execute doesn’t check Terminated and exit. Perhaps TCaptureThread is waiting on the main thread and so the wait on the thread deadlocks.

It’s pretty hard to do anything other than guess, based on your question, but I’d want to check whether or not your code gets past the WaitFor call in the destruction of Thrd. Enable Debug DCUs, set a breakpoint one the call to WaitFor and see for yourself.