PySide QThread moveToThread subclass locks up main thread - python-3.x

Question

I'm having an issue when I try to subclass my worker class the main UI thread locks up and becomes unresponsive until the Worker Thread has finished. I'm at a loss here and suspect something with how the GIL interacts with inheritance?
In MainWindow.clicked() these two lines:
#self.worker = Worker() # This works
self.worker = SubWorker() # This locks up main thread
Here is my sample code that reproduces this:
from PySide import QtGui, QtCore
import sys
import time
class Worker(QtCore.QObject):
started = QtCore.Signal()
progress = QtCore.Signal(int)
finished = QtCore.Signal(bool)
def __init__(self, parent=None):
QtCore.QObject.__init__(self, parent)
self.lock = QtCore.QMutex()
#QtCore.Slot()
def start(self):
self.flag_to_quit = False
try:
self.started.emit()
time.sleep(5)
time.sleep(0.5)
for i in range(10):
self.progress.emit(i)
time.sleep(1)
with QtCore.QMutexLocker(self.lock):
print(self.flag_to_quit)
if self.flag_to_quit:
raise RuntimeError("Requested to quit.")
self.finished.emit(True)
except Exception as ex:
print(ex)
self.finished.emit(False)
finally:
print("start() finished!")
##QtCore.Slot()
def stop(self):
print("Stopping...")
with QtCore.QMutexLocker(self.lock):
self.flag_to_quit = True
#QtCore.Slot()
def __quit_handler(self):
self.flag_to_quit = True
class SubWorker(Worker):
def __init__(self):
Worker.__init__(self)
class MainWindow(QtGui.QWidget):
def __init__(self, parent=None):
QtGui.QWidget.__init__(self, parent)
self.setLayout(QtGui.QVBoxLayout())
self.label = QtGui.QLabel("")
self.layout().addWidget(self.label)
self.button = QtGui.QPushButton("Start Thread")
self.layout().addWidget(self.button)
self.button.clicked.connect(self.clicked)
def closeEvent(self, event):
if hasattr(self, "_thread") and self._thread:
self.worker.flag_to_quit = True
self._thread.quit()
print("waiting for stop...")
self._thread.wait()
self._thread.deleteLater()
#QtCore.Slot()
def worker_started(self):
self.label.setText("Started!")
#QtCore.Slot(int)
def worker_progress(self, interval):
self.label.setText(str(interval))
#QtCore.Slot()
def worker_finished(self, success):
msg = "Finished "
msg += "successfully!" if success else "with errors"
self.label.setText(msg)
#QtCore.Slot()
def clicked(self):
if hasattr(self, "_thread") and self._thread:
self.worker.stop()
self._thread.quit()
print("waiting for stop...")
self._thread.wait()
self._thread.quit()
self._thread.deleteLater()
self._thread = QtCore.QThread()
#self.worker = Worker() # This works
self.worker = SubWorker() # This locks up main thread
self.worker.started.connect (self.worker_started, QtCore.Qt.QueuedConnection)
self.worker.progress.connect(self.worker_progress, QtCore.Qt.QueuedConnection)
self.worker.finished.connect(self.worker_finished, QtCore.Qt.QueuedConnection)
self.worker.moveToThread(self._thread)
self._thread.started.connect(self.worker.start)
self._thread.finished.connect(self.worker.stop)
self._thread.start()
if __name__ == "__main__":
app = QtGui.QApplication(sys.argv)
main_window = MainWindow()
main_window.show()
app.exec_()
sys.exit()
Version information:
Python 3.4.4 (v3.4.4:737efcadf5a6, Dec 20 2015, 19:28:18) [MSC v.1600 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
edit:
Looks like QThread::moveToThread() is failing with Subclasses. this is output of QtCore.QThread.currentThread() in various places:
#self.worker = Worker():
Main:<PySide.QtCore.QThread object at 0x7ff89df384d0>
Real thread: <PySide.QtCore.QThread object at 0x7ff89df383f8>
Worker:<PySide.QtCore.QThread object at 0x7ff89df384d0>
#self.worker = SubWorker()
Main:<PySide.QtCore.QThread object at 0x7f968602c3b0>
Real thread: <PySide.QtCore.QThread object at 0x7f968602c488>
Worker:<PySide.QtCore.QThread object at 0x7f968602c488>

Answer 1

Okay I managed to fix this by doing it the "Wrong" way by inheriting QThread and overriding the run method. I'm not sure why or how but it works.
from PySide import QtGui, QtCore
import sys
import time
class Worker(QtCore.QThread):
_started = QtCore.Signal()
progress = QtCore.Signal(int)
_finished = QtCore.Signal(bool)
def __init__(self, parent=None):
QtCore.QThread.__init__(self, parent)
self.lock = QtCore.QMutex()
#QtCore.Slot()
def run(self):
self.flag_to_quit = False
print("Worker:" + str(QtCore.QThread.currentThread()))
try:
self._started.emit()
time.sleep(2)
for i in range(10):
self.progress.emit(i)
time.sleep(1)
with QtCore.QMutexLocker(self.lock):
if self.flag_to_quit:
raise RuntimeError("Requested to quit.")
self._finished.emit(True)
except Exception as ex:
print(ex)
self._finished.emit(False)
finally:
print("start() finished!")
#QtCore.Slot()
def stop(self):
with QtCore.QMutexLocker(self.lock):
self.flag_to_quit = True
#QtCore.Slot()
def __quit_handler(self):
self.flag_to_quit = True
class SubWorker(Worker):
def __init__(self, parent=None):
Worker.__init__(self, parent)
#QtCore.Slot()
def start(self):
Worker.start(self)
class MainWindow(QtGui.QWidget):
def __init__(self, parent=None):
QtGui.QWidget.__init__(self, parent)
self.setLayout(QtGui.QVBoxLayout())
self.label = QtGui.QLabel("")
self.layout().addWidget(self.label)
self.button = QtGui.QPushButton("Start Thread")
self.layout().addWidget(self.button)
self.button.clicked.connect(self.clicked)
def closeEvent(self, event):
self.hide()
if hasattr(self, "worker") and self.worker:
self.worker.stop()
self.worker.quit()
self.worker.wait()
self.worker.deleteLater()
#QtCore.Slot()
def worker_started(self):
self.label.setText("Started!")
#QtCore.Slot(int)
def worker_progress(self, interval):
self.label.setText(str(interval))
#QtCore.Slot()
def worker_finished(self, success):
msg = "Finished "
msg += "successfully!" if success else "with errors!"
self.label.setText(msg)
def clicked(self):
if hasattr(self, "worker") and self.worker:
self.worker.stop()
self.worker.quit()
self.worker.wait()
self.worker.deleteLater()
print("Main:" + str(QtCore.QThread.currentThread()))
#self.worker = Worker() # This works
self.worker = SubWorker() # This locks up main thread
self.worker._started.connect (self.worker_started)
self.worker.progress.connect(self.worker_progress)
self.worker._finished.connect(self.worker_finished)
self.worker.start()
if __name__ == "__main__":
app = QtGui.QApplication(sys.argv)
main_window = MainWindow()
main_window.show()
app.exec_()
sys.exit()