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PyQt | Signals are not processed in QThread, but in the main thread

In this simple PyQt demo, I emit signals from the main stream. In the workflow, I connect to them, but the signal handlers start in the main thread:

from PyQt4 import QtGui, QtCore
import threading
from time import sleep
import sys


class Data():
    def __init__(self, a, b):
        self.a = a
        self.b = b

    def __str__(self):
        return "Data having %d and %d" % (self.a, self.b)

class Worker(QtCore.QThread):
    def __init__(self, parent):
        QtCore.QThread.__init__(self)
        self.p = parent

    def run(self):
        self.connect(self.p, QtCore.SIGNAL("newTask"), self.task)
        print "[%s] running exec_()" % threading.currentThread()
        self.exec_()

    def task(self, dataobj):
        print "[%s] Processing" % threading.currentThread(), dataobj
        sleep(3)
        print "Done with", dataobj
        self.emit(QtCore.SIGNAL("taskDone"), str(dataobj))

class App(QtCore.QObject):
    def __init__(self):
        QtCore.QObject.__init__(self)
        self.w = Worker(self)
        self.connect(self.w, QtCore.SIGNAL("taskDone"), self.on_task_done)
        self.w.start()

    def assign_tasks(self):
        self.emit(QtCore.SIGNAL("newTask"), Data(3, 4))
        self.emit(QtCore.SIGNAL("newTask"), Data(5, 6))
        print "[%s] Tasks sent" % threading.currentThread()

    @staticmethod
    def on_task_done(objstr):
        print "[%s] App: Worker finished with" % threading.currentThread(), objstr

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    a = App()
    sleep(1)
    a.assign_tasks()
    sleep(20)
    sys.exit(app.exec_())

But the result shows that callbacks are triggered in the main thread:

[<_DummyThread(Dummy-1, started daemon 105564)>] running exec_()
[<_MainThread(MainThread, started 105612)>] Processing Data having 3 and 4
Done with Data having 3 and 4
[<_MainThread(MainThread, started 105612)>] App: Worker finished with Data having 3 and 4
[<_MainThread(MainThread, started 105612)>] Processing Data having 5 and 6
Done with Data having 5 and 6
[<_MainThread(MainThread, started 105612)>] App: Worker finished with Data having 5 and 6
[<_MainThread(MainThread, started 105612)>] Tasks sent

What am I doing wrong? Unfortunately, PyQt docs on this are very incomplete and inconsistent.

I get similar results if I use the method moveToThread:

from PyQt4 import QtGui, QtCore
import threading
from time import sleep
import sys

class Data():
    def __init__(self, a, b):
        self.a = a
        self.b = b

    def __str__(self):
        return "Data having %d and %d" % (self.a, self.b)

class Worker(QtCore.QObject):
    def __init__(self, parent):
        QtCore.QObject.__init__(self)
        self.connect(parent, QtCore.SIGNAL("newTask"), self.task)

    def task(self, dataobj):
        print "[%s] Processing" % threading.currentThread(), dataobj
        sleep(3)
        print "Done with", dataobj
        self.emit(QtCore.SIGNAL("taskDone"), str(dataobj))

    def start(self):
        print "[%s] start()" % threading.currentThread()

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

        self.w = Worker(self)
        self.t = QtCore.QThread(self)
        self.w.moveToThread(self.t)
        self.connect(self.w, QtCore.SIGNAL("taskDone"), self.on_task_done)
        self.connect(self.t, QtCore.SIGNAL("started()"), self.w.start)
        self.t.start()

    def assign_tasks(self):
        self.emit(QtCore.SIGNAL("newTask"), Data(3, 4))
        self.emit(QtCore.SIGNAL("newTask"), Data(5, 6))
        print "[%s] Tasks sent" % threading.currentThread()

    @staticmethod
    def on_task_done(objstr):
        print "[%s] App: Worker finished with" % threading.currentThread(), objstr

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    a = App()
    sleep(1)
    a.assign_tasks()
    sleep(20)
    sys.exit(app.exec_())

Result:

[<_DummyThread(Dummy-1, started daemon 108992)>] start()
[<_MainThread(MainThread, started 107004)>] Processing Data having 3 and 4
Done with Data having 3 and 4
[<_MainThread(MainThread, started 107004)>] App: Worker finished with Data having 3 and 4
[<_MainThread(MainThread, started 107004)>] Processing Data having 5 and 6
Done with Data having 5 and 6
[<_MainThread(MainThread, started 107004)>] App: Worker finished with Data having 5 and 6
[<_MainThread(MainThread, started 107004)>] Tasks sent
+4
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1 answer

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  • Worker QObject, QThread
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  • python qt. threading.currentThread qt. QThread.currentThread() .
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, , :

from PyQt4 import QtGui, QtCore
import threading
from time import sleep
import sys

class Data():
    def __init__(self, a, b):
        self.a = a
        self.b = b

    def __str__(self):
        return "Data having %d and %d" % (self.a, self.b)

class Worker(QtCore.QObject):

    taskDone = QtCore.pyqtSignal(str)

    def __init__(self, parent):
        QtCore.QObject.__init__(self)
        parent.newTask.connect(self.task)

    @QtCore.pyqtSlot(object)
    def task(self, dataobj):
        print "[%s] Processing" % QtCore.QThread.currentThread().objectName(), dataobj
        sleep(3)
        print "Done with", dataobj
        self.taskDone.emit(str(dataobj))

    @QtCore.pyqtSlot()
    def start(self):
        print "[%s] start()" % QtCore.QThread.currentThread().objectName()

class App(QtCore.QObject):

    newTask = QtCore.pyqtSignal(object)

    def __init__(self):
        QtCore.QObject.__init__(self)
        self.w = Worker(self)
        self.t = QtCore.QThread(self, objectName='workerThread')
        self.w.moveToThread(self.t)
        self.w.taskDone.connect(self.on_task_done)
        self.t.started.connect(self.w.start)
        self.t.start()

    def assign_tasks(self):
        self.newTask.emit(Data(3, 4))
        self.newTask.emit(Data(5, 6))
        print "[%s] Tasks sent" % QtCore.QThread.currentThread().objectName()

    @staticmethod
    def on_task_done(objstr):
        print "[%s] App: Worker finished with" % QtCore.QThread.currentThread().objectName(), objstr

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    QtCore.QThread.currentThread().setObjectName('main')
    a = App()
    sleep(1)
    a.assign_tasks()
    from utils import sigint
    sys.exit(app.exec_())

objectName, :

[workerThread] start()
[main] Tasks sent
[workerThread] Processing Data having 3 and 4
Done with Data having 3 and 4
[workerThread] Processing Data having 5 and 6
[main] App: Worker finished with Data having 3 and 4
Done with Data having 5 and 6
[main] App: Worker finished with Data having 5 and 6
+9

Source: https://habr.com/ru/post/1541005/

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