CODEWITHSUNDEEP
multithreadingdelphi
Wolfgang Bures
Wolfgang Bures

Reputation: 717

How can a worker thread end the application?

I seem to have the challenge that a worker thread knows to close the application, but neither PostQuitMessage() nor Application.Terminate() seem to work. The Application just doesn't quit, no errors.

Do I have to set a flag to call one of these from the main thread, or is there another trick?

The thread checks for an updated version and calls an updater to replace the .exe (once it's not locked anymore). After calling the updater, it needs to quit the application.

Upvotes: 1

Views: 459

Answers (2)

Rob Lambden
Rob Lambden

Reputation: 2293

Remy has a great answer.

If you are using The Delphi Threads (your threads derive from TThread) then you can use the Synchronize method of your thread to run a routine in the context of the main thread, and then in that routine (which is run by the main thread) you can call Application.Terminate

See: http://docwiki.embarcadero.com/Libraries/Sydney/en/System.Classes.TThread.Synchronize

Upvotes: 0

Remy Lebeau
Remy Lebeau

Reputation: 595782

PostQuitMessage() posts a WM_QUIT message to the message queue of the calling thread. Application.Terminate() uses PostQuitMessage(). That is why neither is working in your case, since you are calling them in the wrong thread context.

So, you can either:

  • flag the main thread to call PostQuitMessage()/Application.Terminate() at its earliest conventience, such as with TThread.Queue():

    TThread.Queue(nil, Application.Terminate);

  • post your own WM_QUIT message to the main thread or Application window, ie:

    PostThreadMessage(MainThreadID, WM_QUIT, 0, 0);

    PostMessage(Application.Handle, WM_QUIT, 0, 0);

  • post a WM_CLOSE message to your MainForm window (if you have one) 1, as closing the MainForm will terminate the Application, ie:

    PostMessage(Application.MainForm.Handle, WM_CLOSE, 0, 0);

    1: just be careful with this one! The TWinControl.Handle property is not thread-safe. If you read the MainForm's Handle property in a worker thread while the main thread is in the process of (re-)creating the window, bad things can happen!

Upvotes: 5

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