PyQT Application Hangs when UI is Closed

Question

I'm currently having trouble when trying to close my application. As of now, my application currently spawns and thread that runs in a while loop (while True loop), while my main thread initializes and runs the UI in PyQT.

def main():

    group_size = 8 
    buffer_size = 4 
    app = QtGui.QApplication(sys.argv)
    dgui = DirectGui(group_size, buffer_size)
    engine = KCluster_Engine(group_size, buffer_size)
    dgui.set_engine_ref(engine)
    engine.assign_interface(dgui)
    thread = Thread(target = engine.start)
    thread.start()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

When I close out of my main window of my application in PyQT, the command that spawned the python script in the shell cannot be stopped, even with a ctrl-c.

What is the best way to deal with this behavior? When I close my application, I also want the spawned thread to stop, join and quit this process. How do I do this?

most probably that thread is stuck somewhere. put logs there and see whats happening — Abhishek Bansal, May 23 '14 at 03:02
@AbhishekBansal I know for a fact its spinning on a while True loop. Is there anyway to call it to stop after quitting the application? — jab, May 23 '14 at 03:16

score 2 · Accepted Answer · edited May 23 '17 at 12:27

According to the Python Standard Library, you have two ways of killing your thread :

either you make it daemonic (thread.daemaon = True) and it will be killed without any possibility of proper cleaning
or you use a signaling method like Event that you test in appropriate places in you thread

But I think you should have a look to this older (but still of actuality ...) question in SO : Is there any way to kill a Thread in Python?

All this supposes that app.exec_() returns properly in your main thread.

score 1 · Answer 2 · answered May 23 '14 at 06:51

1

If you make the thread daemonic it's going to stop after you exit the application. Put thread.daemon = True before starting it (if you do it after calling start an exception will be raised). It should work fine with threads from the threading module.

answered May 23 '14 at 06:51

Mátyás Kuti

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PyQT Application Hangs when UI is Closed

2 Answers2