Delphi - What happens with un-freed (but terminated) thread when application exits?

Question

I have multithreaded application and I've got a little problem when application ends: I can correctly terminate the thread by calling TThread.Terminate method in Form1.OnDestroy event handler, but the termination does take some time and so I can't free the memory (by TThread.Free method). Unfortunately for some other reason I must have TThread.FreeOnTerminate property set to false, so the thread object isn't destroyed automatically after thread termination.

My question is probably a little silly and I should have known it a long time ago, but is this ok and the thread will be destroyed automatically (since the application just ends), or is it a problem and the memory would be "lost"? Thanks a lot for explanation.

Answer 1

You should wait for the thread to terminate before you begin the process off shutting down the rest of your application, otherwise shared resources may be freed under the threads feet, possibly leading to a string of access violations. After you have waited for thread termination, then you can free it. In fact, that's what the TThread destructor does for you.

If there are no shared resources, then sure, let it die by itself. Even if the thread terminates after the main thread, all that is required is that all your threads exit for the program to terminate. Any memory associated with the thread's object will just get cleaned up and given back to the OS with everything else.

BUT, be careful! If your thread is taking a while to exit, it can lead to a zombie process sitting there churning away without a GUI. That is why it is very important to check the Terminated flag very often in the thread loop, and exit the thread.

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