I have this code (if you have pyqt5, you should be able to run it yourself):
import sys
import time
from PyQt5.QtWidgets import QApplication, QPushButton, QVBoxLayout, QWidget
from PyQt5.QtCore import QObject, QThread, pyqtSignal, pyqtSlot
class Worker(QObject):
def __init__(self):
super().__init__()
self.thread = None
class Tab(QObject):
def __init__(self, _main):
super().__init__()
self._main = _main
class WorkerOne(Worker):
finished = pyqtSignal()
def __init__(self):
super().__init__()
@pyqtSlot(str)
def print_name(self, name):
for _ in range(100):
print("Hello there, {0}!".format(name))
time.sleep(1)
self.finished.emit()
self.thread.quit()
class SomeTabController(Tab):
def __init__(self, _main):
super().__init__(_main)
self.threads = {}
self._main.button_start_thread.clicked.connect(self.start_thread)
# Workers
self.worker1 = WorkerOne()
#self.worker2 = WorkerTwo()
#self.worker3 = WorkerThree()
#self.worker4 = WorkerFour()
def _threaded_call(self, worker, fn, *args, signals=None, slots=None):
thread = QThread()
thread.setObjectName('thread_' + worker.__class__.__name__)
# store because garbage collection
self.threads[worker] = thread
# give worker thread so it can be quit()
worker.thread = thread
# objects stay on threads after thread.quit()
# need to move back to main thread to recycle the same Worker.
# Error is thrown about Worker having thread (0x0) if you don't do this
worker.moveToThread(QThread.currentThread())
# move to newly created thread
worker.moveToThread(thread)
# Can now apply cross-thread signals/slots
#worker.signals.connect(self.slots)
if signals:
for signal, slot in signals.items():
try:
signal.disconnect()
except TypeError: # Signal has no slots to disconnect
pass
signal.connect(slot)
#self.signals.connect(worker.slots)
if slots:
for slot, signal in slots.items():
try:
signal.disconnect()
except TypeError: # Signal has no slots to disconnect
pass
signal.connect(slot)
thread.started.connect(lambda: fn(*args)) # fn needs to be slot
thread.start()
@pyqtSlot()
def _receive_signal(self):
print("Signal received.")
@pyqtSlot(bool)
def start_thread(self):
name = "Bob"
signals = {self.worker1.finished: self._receive_signal}
self._threaded_call(self.worker1, self.worker1.print_name, name,
signals=signals)
class MainWindow(QWidget):
def __init__(self):
super().__init__()
self.setWindowTitle("Thread Example")
form_layout = QVBoxLayout()
self.setLayout(form_layout)
self.resize(400, 400)
self.button_start_thread = QPushButton()
self.button_start_thread.setText("Start thread.")
form_layout.addWidget(self.button_start_thread)
self.controller = SomeTabController(self)
if __name__ == '__main__':
app = QApplication(sys.argv)
_main = MainWindow()
_main.show()
sys.exit(app.exec_())
However WorkerOne still blocks my GUI thread and the window is non-responsive when WorkerOne.print_name is running.
I have been researching a lot about QThreads recently and I am not sure why this isn't working based on the research I've done.
What gives?
The problem is caused by the connection with the lambda method since this lambda is not part of the Worker so it does not run on the new thread. The solution is to use functools.partial:
from functools import partial
...
thread.started.connect(partial(fn, *args))
Complete Code:
import sys
import time
from functools import partial
from PyQt5.QtWidgets import QApplication, QPushButton, QVBoxLayout, QWidget
from PyQt5.QtCore import QObject, QThread, pyqtSignal, pyqtSlot
class Worker(QObject):
def __init__(self):
super().__init__()
self.thread = None
class Tab(QObject):
def __init__(self, _main):
super().__init__()
self._main = _main
class WorkerOne(Worker):
finished = pyqtSignal()
def __init__(self):
super().__init__()
@pyqtSlot(str)
def print_name(self, name):
for _ in range(100):
print("Hello there, {0}!".format(name))
time.sleep(1)
self.finished.emit()
self.thread.quit()
class SomeTabController(Tab):
def __init__(self, _main):
super().__init__(_main)
self.threads = {}
self._main.button_start_thread.clicked.connect(self.start_thread)
# Workers
self.worker1 = WorkerOne()
#self.worker2 = WorkerTwo()
#self.worker3 = WorkerThree()
#self.worker4 = WorkerFour()
def _threaded_call(self, worker, fn, *args, signals=None, slots=None):
thread = QThread()
thread.setObjectName('thread_' + worker.__class__.__name__)
# store because garbage collection
self.threads[worker] = thread
# give worker thread so it can be quit()
worker.thread = thread
# objects stay on threads after thread.quit()
# need to move back to main thread to recycle the same Worker.
# Error is thrown about Worker having thread (0x0) if you don't do this
worker.moveToThread(QThread.currentThread())
# move to newly created thread
worker.moveToThread(thread)
# Can now apply cross-thread signals/slots
#worker.signals.connect(self.slots)
if signals:
for signal, slot in signals.items():
try:
signal.disconnect()
except TypeError: # Signal has no slots to disconnect
pass
signal.connect(slot)
#self.signals.connect(worker.slots)
if slots:
for slot, signal in slots.items():
try:
signal.disconnect()
except TypeError: # Signal has no slots to disconnect
pass
signal.connect(slot)
thread.started.connect(partial(fn, *args)) # fn needs to be slot
thread.start()
@pyqtSlot()
def _receive_signal(self):
print("Signal received.")
@pyqtSlot(bool)
def start_thread(self):
name = "Bob"
signals = {self.worker1.finished: self._receive_signal}
self._threaded_call(self.worker1, self.worker1.print_name, name,
signals=signals)
class MainWindow(QWidget):
def __init__(self):
super().__init__()
self.setWindowTitle("Thread Example")
form_layout = QVBoxLayout()
self.setLayout(form_layout)
self.resize(400, 400)
self.button_start_thread = QPushButton()
self.button_start_thread.setText("Start thread.")
form_layout.addWidget(self.button_start_thread)
self.controller = SomeTabController(self)
if __name__ == '__main__':
app = QApplication(sys.argv)
_main = MainWindow()
_main.show()
sys.exit(app.exec_())