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Terminating QThread gracefully on QDialog reject ()

I have a QDialog that creates QThread to do some work, while preserving a user interface based on the structure given here: How to really use QThreads; Full explanation . However, if reject () is called (due to the user clicking cancel or closing the dialog) while the thread is still running, I get an error message:

QThread: destroyed while the thread is still running

What I would like to do is that the worker cycle is interrupted earlier, and then does some cleaning in the background (for example, clear some queues, emit a signal). I managed to do this using my own “cancel” function, but how do I get it to play well with reject () (and all kinds of ways to call it)? I do not want the dialog to block waiting for cleanup - it should just work in the background and then exit gracefully.

See the sample code below that shows the problem. Any help would be greatly appreciated.

#!/usr/bin/env python

from PyQt4 import QtCore, QtGui
import sys
import time

class Worker(QtCore.QObject):
    def __init__(self):
        QtCore.QObject.__init__(self)

    def process(self):
        # dummy worker process
        for n in range(0, 10):
            print 'process {}'.format(n)
            time.sleep(0.5)
        self.finished.emit()

    finished = QtCore.pyqtSignal()

class Dialog(QtGui.QDialog):
    def __init__(self):
        QtGui.QDialog.__init__(self)
        self.init_ui()

    def init_ui(self):
        self.layout = QtGui.QVBoxLayout(self)
        self.btn_run = QtGui.QPushButton('Run', self)
        self.layout.addWidget(self.btn_run)
        self.btn_cancel = QtGui.QPushButton('Cancel', self)
        self.layout.addWidget(self.btn_cancel)

        QtCore.QObject.connect(self.btn_run, QtCore.SIGNAL('clicked()'), self.run)
        QtCore.QObject.connect(self.btn_cancel, QtCore.SIGNAL('clicked()'), self.reject)

        self.show()
        self.raise_()

    def run(self):
        # start the worker thread
        self.thread = QtCore.QThread()
        self.worker = Worker()
        self.worker.moveToThread(self.thread)
        QtCore.QObject.connect(self.thread, QtCore.SIGNAL('started()'), self.worker.process)
        QtCore.QObject.connect(self.worker, QtCore.SIGNAL('finished()'), self.thread.quit)
        QtCore.QObject.connect(self.worker, QtCore.SIGNAL('finished()'), self.worker.deleteLater)
        QtCore.QObject.connect(self.thread, QtCore.SIGNAL('finished()'), self.thread.deleteLater)
        self.thread.start()

def main():
    app = QtGui.QApplication(sys.argv)
    dlg = Dialog()
    ret = dlg.exec_()

if __name__ == '__main__':
    main()
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1 answer

Your problem: self.threadPython is freed after the dialog is closed or the cancel button is pressed and the Qt thread is still running.

, . ,


    def run(self):
        # start the worker thread
        self.thread = QtCore.QThread(self)
        self.worker = Worker()
        self.worker.moveToThread(self.thread)
        QtCore.QObject.connect(self.thread, QtCore.SIGNAL('started()'), self.worker.process)
        QtCore.QObject.connect(self.worker, QtCore.SIGNAL('finished()'), self.thread.quit)
        QtCore.QObject.connect(self.worker, QtCore.SIGNAL('finished()'), self.worker.deleteLater)
        QtCore.QObject.connect(self.thread, QtCore.SIGNAL('finished()'), self.thread.deleteLater)
        self.thread.start()

Qt PyQt , , GC, Qt . , Qt .

, , .
:

class Worker(QtCore.QObject):
    def __init__(self):
        QtCore.QObject.__init__(self)

    def process(self):
        # dummy worker process
        self.flag = False
        for n in range(0, 10):
            if self.flag:
                print 'stop'
                break
            print 'process {}'.format(n)
            time.sleep(0.5)
        self.finished.emit()

    finished = QtCore.pyqtSignal()

class Dialog(QtGui.QDialog):
    def __init__(self, parent=None):
        QtGui.QDialog.__init__(self, parent)
        self.init_ui()

    def init_ui(self):
        self.layout = QtGui.QVBoxLayout(self)
        self.btn_run = QtGui.QPushButton('Run', self)
        self.layout.addWidget(self.btn_run)
        self.btn_cancel = QtGui.QPushButton('Cancel', self)
        self.layout.addWidget(self.btn_cancel)

        QtCore.QObject.connect(self.btn_run, QtCore.SIGNAL('clicked()'), self.run)
        QtCore.QObject.connect(self.btn_cancel, QtCore.SIGNAL('clicked()'), self.reject)

        QtCore.QObject.connect(self, QtCore.SIGNAL('rejected()'), self.stop_worker)

        self.show()
        self.raise_()

    def stop_worker(self):
        print 'stop'
        self.worker.flag = True

    def run(self):
        # start the worker thread
        self.thread = QtCore.QThread(self)
        self.worker = Worker()
        self.worker.moveToThread(self.thread)
        QtCore.QObject.connect(self.thread, QtCore.SIGNAL('started()'), self.worker.process)
        QtCore.QObject.connect(self.worker, QtCore.SIGNAL('finished()'), self.thread.quit)
        QtCore.QObject.connect(self.worker, QtCore.SIGNAL('finished()'), self.worker.deleteLater)
        QtCore.QObject.connect(self.thread, QtCore.SIGNAL('finished()'), self.thread.deleteLater)
        self.thread.start()
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