PySide2 Grandchild Threads

grandchild_threads.py

import sys

import shiboken2
from PySide2.QtCore import QObject, QThread, Signal, Qt
from PySide2.QtWidgets import QApplication, QPushButton


class Grandchild(QObject):
    def __init__(self, parent=None):
        super(Grandchild, self).__init__(parent)
        print('Grandchild()')

    def __del__(self):
        print('~Grandchild()')


class Child(QObject):
    _thread = None
    _worker = None

    def __init__(self, parent=None):
        super(Child, self).__init__(parent)
        print('Child()')

    def __del__(self):
        print('~Child()')
        if shiboken2.isValid(self._thread):
            self.stop_thread()

    def start_thread(self):
        print('Starting grandchild thread')
        self._thread = QThread(self)
        self._worker = Grandchild()
        self._worker.moveToThread(self._thread)
        self._thread.finished.connect(self._worker.deleteLater)
        self._thread.start()

    def stop_thread(self):
        print('Stopping grandchild thread')
        self._thread.quit()
        self._thread.wait()

    def toggle_thread(self):
        if self._thread and self._thread.isRunning():
            self.stop_thread()
        else:
            self.start_thread()


class Parent(QPushButton):
    _thread = None
    _worker = None

    stop_child = Signal()

    def __init__(self, parent=None):
        super(Parent, self).__init__(parent)
        print('Parent()')
        self.setText('Start Grandchild')

        self._thread = QThread(self)
        self._worker = Child()
        self._worker.moveToThread(self._thread)
        self._thread.finished.connect(self._worker.deleteLater)
        self._thread.start()

        self.clicked.connect(self.on_push)
        self.clicked.connect(self._worker.toggle_thread)
        self.stop_child.connect(self._worker.stop_thread, Qt.BlockingQueuedConnection)

    def __del__(self):
        print('~Parent()')
        self.stop_child.emit()
        if shiboken2.isValid(self._thread):
            self._thread.quit()
            self._thread.wait()

    def on_push(self):
        if self.text() == 'Start Grandchild':
            self.setText('Stop Grandchild')
        else:
            self.setText('Start Grandchild')


def main():
    app = QApplication(sys.argv)

    widget = Parent()
    widget.show()
    sys.exit(app.exec_())


if __name__ == "__main__":
    main()