CODEWITHSUNDEEP
pythonmultithreadingqtpyside
Doug T.
Doug T.

Reputation: 65609

When a QThread has an event queue, is it safe to terminate the thread with exit()?

I'm using QThread to do some periodic background work, the source code looks something like this

class Worker(QObject):
    """ Separate QObject that does the work with affinity of 
        'DoStuffOnceASecond'"""
    def __init__(self):
        super(QWorker, self).__init__()

    def doWork(self):
        #... do work, post signal to consumer


class DoStuffOnceASecond(QThread):
    def __init__(self):
        super(DoStuffOnceASecond, self).__init__()   

    def run(self):
        """ Setup "pullFiles" to be called once a second"""
        self.timer= QTimer()
        self.worker = Worker()
        self.timer.setSingleShot(False)
        self.timer.timeout.connect(self.worker.doWork)
        self.timer.start(1000)
        self.exec_()

I'm looking for the best way to terminate such a thread. One option would be to post a signal from the main thread to this thread, creating a slot in this thread. Since these slots execute as part of the event loop, they would get safely picked up. But then I'd be self terminating... and I'm not sure if that would work very well.

Or I'm wondering, since the thread should be conscious that its running an event loop, if its safe just to call exit() on this thread? The documentation seems to indicate this is ok:

After calling this function, the thread leaves the event loop and returns from the call to QEventLoop::exec(). The QEventLoop::exec() function returns returnCode.

I think "leaves the event loop" means it will allow the current event to finish processing. Or does the QThread instantly terminate?

The code here is python (pyside 1.10, python 2.7) but this could easily apply to any QT code using QThread.

Upvotes: 2

Views: 1318

Answers (1)

Pavel Zdenek
Pavel Zdenek

Reputation: 7293

You don't need to declare any extra slots, if you don't mind that your return code will be 0. Then you can use already defined quit() slot which just calls exit(0) on your thread. About your fear to "self-terminate" - you are not terminating the thread, just quitting its event loop. And you can start it anytime by calling exec() again. You are still very nice to your thread so everything should "work very well". Instant termination is possible by QThread::terminate but is meant as last desperate mean to kill off the thread when the above method has failed.

Upvotes: 1

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