GUI freezing with PySide and multiprocessing

Question

I am trying to offload a heavy background job to a multiprocessing process. I just want the separate process to be able to report it's progress to my GUI. Here's my last try, the GUI is simple, a couple of buttons and a progress bar:

from PySide.QtGui import *
from PySide.QtCore import *
import sys
from multiprocessing import Process, Pipe
import time

class WorkerClass:
#This class has the job to run
    def worker(self, pipe):
        for i in range(101):
            pipe.send(i)
            time.sleep(.02)

class WorkStarter(QThread):
#this thread takes a widget and updates it using progress sent from
#process via Pipe
    def __init__(self, progressBar):
        super().__init__()
        self.progress_bar = progressBar

    def run(self):
        worker_obj = WorkerClass()
        myend, worker_end = Pipe(False)
        self.p = Process(target=worker_obj.worker, args=(worker_end,))
        self.p.start()
        while True:
            val = myend.recv()
            self.progress_bar.setValue(val)
            if val == 100:
                break

class WorkingWidget(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setWindowTitle('Blue collar widget')
        layout = QHBoxLayout()
        start_btn = QPushButton('Start working')
        start_btn.clicked.connect(self.startWorking)
        end_btn = QPushButton('End working')
        end_btn.clicked.connect(self.endWorking)
        layout.addWidget(start_btn)
        layout.addWidget(end_btn)
        self.progress_bar = QProgressBar()
        layout.addWidget(self.progress_bar)
        self.setLayout(layout)

    def startWorking(self):
        self.thread = WorkStarter(self.progress_bar)
        self.thread.start()

    def endWorking(self):
        self.thread.terminate()

if __name__ == '__main__':
    app = QApplication(sys.argv)
    main = WorkingWidget()
    main.show()
    sys.exit(app.exec_())

I cannot pass any QObject as an argument to the process, since that is not pickleable:

#cannot do the following
...
def startWorking(self):
    self.worker_obj = WorkerClass()
    #pass the progress bar to the process and the process updates the bar
    self.p = Process(target=self.worker_obj.worker, args=(self.progress_bar,))

The problem is that this gui some times works, other times it freezes (So please press 'start' multiple times until it freezes :) ), and here on Windows it says : pythonw.exe has stopped working... Any clue what's the reason for that?. I cannot figure it out by myself. Thanks

I think I have a working example, see my post here: http://stackoverflow.com/questions/15698251/multiprocessing-gui-schemas-to-combat-the-not-responding-blocking/19296108#19296108 — Caleb Hattingh, Oct 10 '13 at 13:11
I thank you for you attention, but that doesn't answer the question, Why does this work some times and crash some other times? — MadeOfAir, Oct 11 '13 at 19:44

score 2 · Answer 1 · edited Apr 13 '17 at 12:33

2

You are not supposed to create the object inside "run" method of QThread, emit signal from "run", implement a function say "callerFunction" create object in this function and finally call this function on signal which is emitted by the "run" function.

You can emit the signal in the while loop that you have already created.
Have a look at this solution
don't create a python process, QThread is sufficient for this job

edited Apr 13 '17 at 12:33

Community

1
1

answered Sep 29 '13 at 07:51

qurban

3,885
24
36

Sorry, you didn't clarify why the gui does freeze. But i'll check the link you provided when i have the chance. – MadeOfAir Sep 29 '13 at 18:24
Sorry, the example you pointed at is just stupid. I don't have PyQt installed, but I don't think by moving the line that runs the thread from inside the class to outside will do any magic. – MadeOfAir Oct 01 '13 at 21:50
1

Sorry for late but I always do this what I told you and it always worked fine for me. – qurban Oct 19 '13 at 17:41

GUI freezing with PySide and multiprocessing

1 Answers1