I have a long running task, which for example's sake I have made an infinite while loop:
def long_task(parent, progress_callback):
top = 100000
x = 0
while True:
if x < top:
if not parent.stop:
progress_callback.emit(x)
x += 1
else:
break
else:
x = 0
progress_callback.emit(x)
x += 1
I have a Worker class that subclasses QRunnable, and then I can override the run() method with whatever function is passed to the Worker.
class ThreadWorker(QtCore.QRunnable):
def __init__(self, fn, *args, **kwargs):
super(ThreadWorker, self).__init__()
self.fn = fn
self.args = args
self.kwargs = kwargs
self.signals = ThreadWorkerSignals()
self.kwargs['progress_callback'] = self.signals.progress
self.running = False
@QtCore.pyqtSlot()
def run(self):
self.running = True
try:
result = self.fn(*self.args, **self.kwargs)
except:
traceback.print_exc()
exctype, value = sys.exc_info()[:2]
self.signals.error.emit((exctype, value, traceback.format_exc()))
else:
self.signals.result.emit(result) # Return the result of the processing
finally:
self.signals.finished.emit() # Done
I create two instances of Worker within my MainWindow, and pass the same long-running task to each worker. Both workers are added to my MainWindow's QThreadPool and then I call start(worker) on each to begin the worker's run() method. I now have two threads running the infinite loop:
class MainWindow(QtWidgets.QMainWindow):
def __init__(self):
super().__init__()
## NOT SHOWING THE REST OF INIT CODE
def create_workers(self):
self.worker1 = ThreadWorker(self.long_task, parent=self)
self.worker1.signals.progress.connect(lambda x: self.long_label_1.setText(str(x)))
self.worker2 = ThreadWorker(self.long_task, parent=self)
self.worker2.signals.progress.connect(lambda x: self.long_label_2.setText(str(x)))
self.threadpool.start(self.worker1)
self.threadpool.start(self.worker2)
self.stop = False
Please note the self.stop attribute above - this also belongs to the MainWindow class.
All I want to do is break the loop (interrupt the run() method of a worker) when I press a button.
As you can see, I am referencing parent.stop during every iteration of the worker's while loop. Right now, if I press my button, MainWindow's stop attribute turns True and the loop breaks when the worker class sees this change.
def stop_tasks(self):
self.stop = True
This works fine and accomplishes my goal, but I am wondering if this is dangerous and if there is a better way to do this? I only ask because it seems risky to reference an outside class attribute from within a separate running thread, and I don't know what could go wrong.
