This question already has answers here:
PyQt: Connecting a signal to a slot to start a background operation
(3 answers)
Closed 5 years ago.
So having followed my best understanding of how to correctly use threads in Qt, I've written a small toy example in which a QObject is moved to a running thread and a signal is called on that object when the window is clicked.
The problem I'm having is the slot is never called in the correct thread - it is always called in the main thread.
This is implemented with the following code:
from PyQt5 import QtWidgets, QtCore
class WidgetWithInput(QtWidgets.QWidget):
widgetClicked = QtCore.pyqtSignal()
def mousePressEvent(self, event):
self.widgetClicked.emit()
class MyObject(QtCore.QObject):
aSignal = QtCore.pyqtSignal()
def __init__(self, *args, **kwargs):
super(MyObject, self).__init__(*args, **kwargs)
self.aSignal.connect(self.onASignal)
def onASignal(self):
print('MyObject signal thread: %s'
% str(int(QtCore.QThread.currentThreadId())))
class SimpleDisplay(QtWidgets.QMainWindow):
''' Class presenting the display subsytem
'''
def __init__(self, my_object, *args, **kwargs):
super(SimpleDisplay, self).__init__(*args, **kwargs)
self._my_object = my_object
self._widget = WidgetWithInput()
self.setCentralWidget(self._widget)
self._widget.widgetClicked.connect(self._do_something)
def _do_something(self):
self._my_object.aSignal.emit()
def main(run_until_time=None):
import sys
app = QtWidgets.QApplication(sys.argv)
print ('main thread: %s' % str(int(QtCore.QThread.currentThreadId())))
concurrent_object = MyObject()
display = SimpleDisplay(concurrent_object)
myobject_thread = QtCore.QThread()
myobject_thread.start()
concurrent_object.moveToThread(myobject_thread)
display.show()
exit_status = app.exec_()
myobject_thread.quit()
myobject_thread.wait()
sys.exit(exit_status)
if __name__ == '__main__':
main()
Which outputs something like:
main thread: 139939383113472
MyObject signal thread: 139939383113472
I would expect those two printed thread ids to be different.
Am I missing something here? Explicitly setting the signal to be queued doesn't change anything.
With thanks to #three_pinapples, his suggestion in the comments solves the problem: The slot needs to be decorated with QtCore.pyqtSlot:
class MyObject(QtCore.QObject):
aSignal = QtCore.pyqtSignal()
def __init__(self, *args, **kwargs):
super(MyObject, self).__init__(*args, **kwargs)
self.aSignal.connect(self.onASignal)
#QtCore.pyqtSlot()
def onASignal(self):
print('MyObject signal thread:\t %s'
% str(int(QtCore.QThread.currentThreadId())))
Related
I'm working in a data processing desktop application with Python 3.7 and PySide2 on which requires me to load data from several large (approx 250k rows) excel files into the program's processing library. For this I've set up in my application a simple popup (called LoadingPopup) which includes a rotating gif and a simple caption, and also some code that loads the data from the excel files into a global object using pandas. Both of these things work as intended when run on their own, but if I happen to create a loading dialog and a QRunnable worker in the same scope of my codebase, the widgets contained in loading widget (a gif and a simple caption) will simply not show.
I've tried changing the parent type for my widget from QDialog to QWidget, or initializing the popup (the start() function) both outside and inside the widget. I'm not very experienced with Qt5 so I don't know what else to do.
import sys, time, traceback
from PySide2.QtWidgets import *
from PySide2.QtCore import *
from PySide2.QtGui import *
from TsrUtils import PathUtils
class WorkerSignals(QObject):
finished = Signal()
error = Signal(tuple)
result = Signal(object)
class TsrWorker(QRunnable):
def __init__(self, fn, *args, **kwargs):
super(TsrWorker, self).__init__()
self.fn = fn
self.args = args
self.kwargs = kwargs
self.signals = WorkerSignals()
#Slot()
def run(self):
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)
finally:
self.signals.finished.emit()
class LoadingPopup(QWidget):
def __init__(self):
super().__init__()
self.message = "Cargando"
self.setMinimumSize(350,300)
self.setWindowIcon(\
QIcon(PathUtils.ruta_absoluta('resources/icons/tsr.png')))
self.setWindowTitle(self.message)
self.layout = QVBoxLayout(self)
self.setLayout(self.layout)
self.movie = QMovie(self)
self.movie.setFileName("./resources/img/spinner.gif")
self.movie.setCacheMode(QMovie.CacheAll)
self.movie.start()
self.loading = QLabel(self)
self.loading.setMovie(self.movie)
self.loading.setAlignment(Qt.AlignCenter)
self.layout.addWidget(self.loading)
self.lbl = QLabel(self.message, self)
self.lbl.setAlignment(Qt.AlignCenter)
self.lbl.setStyleSheet("font: 15pt")
self.layout.addWidget(self.lbl)
class MyMainApp(QApplication):
def __init__(self, args):
super().__init__()
self.l = LoadingPopup()
self.l.show()
w = TsrWorker(time.sleep, 5)
w.signals.finished.connect(self.terminado)
w.run()
def terminado(self):
print('timer finished')
self.l.hide()
if __name__ == '__main__':
app = MyMainApp(sys.argv)
sys.exit(app.exec_())
I've changed the actual data loading part of the application in the example with a time.sleep function. MY expected results are that I should be able to have the LoadingPopup show up with a gif moving, and then it should close once the QRunnable finishes.
You should not call the run method directly since you will have the heavy task run on the GUI thread freezing it. You must launch it using QThreadPool:
class MyMainApp(QApplication):
def __init__(self, args):
super().__init__()
self.l = LoadingPopup()
self.l.show()
w = TsrWorker(time.sleep, 5)
w.signals.finished.connect(self.terminado)
# w.run()
QThreadPool.globalInstance().start(w) # <---
def terminado(self):
print('timer finished')
self.l.hide()
It's maybe a stupid question but why I can not emit a signal self.printSecondSignal.emit('TEST2') in the Worker class. What I want to do is: Calling the function do_some_calc() (connecteded over QPushButton clicked() signal) from TestMain class and in Worker class, want to emit a signal to update the Gui in TestMain. But I get AttributeError: TestMain object has no attribute printSecondSignal. Emitting the signal self.printFirstSignal.emit('TEST1') works without any problem
TestMain.py
from source.Manager.TestManager import *
class TestMain(QMainWindow):
def __init__(self, parent= None):
super(TestMain, self).__init__(parent)
# import ui
loadUi('../gui/testGui.ui', self)
self.manager= TestManager()
self.thread= QThread()
self.manager.moveToThread(self.thread)
self.manager.finished.connect(self.thread.quit)
self.thread.started.connect(self.manager.first_slot)
self.thread.start()
self.manager.printFirstSignal.connect(self.print_onTextEdit)
self.offlinePushButton.clicked.connect(self.offline_slot)
self.manager.printSecondSignal.connect(self.print_onTextEdit)
def offline_slot(self):
manager.do_some_calc(self)
def print_onTextEdit(self, str):
self.outputTextEdit.append(str)
Manager.py
class TestManager(QObject): #QtCore.QThread
finished= pyqtSignal()
printFirstSignal= pyqtSignal(str)
printSecondSignal= pyqtSignal(str)
def __init__(self, parent= None):
super(TestManager, self).__init__(parent)
def first_slot(self):
self.printFirstSignal.emit('TEST1')
self.finished.emit()
def do_some_calc(self):
do_sometingelse()
try:
self.printSecondSignal.emit('TEST2')
except :
traceback.print_exc()
As you were told in the other question you asked about this same code, all communication between threads has to be done through use of a signal. In your offline_slot method you attempt to call the manager.do_some_calc() directly while the manager instance is operating in another thread. This communication will have to be done with a signal. It would look something like this:
class TestMain(QMainWindow):
do_some_calc_signal = pyqtSignal()
def __init__(self, parent=None):
super(TestMain, self).__init__(parent)
# import ui
loadUi('../gui/testGui.ui', self)
self.manager= TestManager()
self.thread= QThread()
self.manager.moveToThread(self.thread)
self.do_some_calc_signal.connect(self.manager.do_some_calc)
self.manager.finished.connect(self.thread.quit)
self.thread.started.connect(self.manager.first_slot)
self.thread.start()
self.manager.printFirstSignal.connect(self.print_onTextEdit)
self.offlinePushButton.clicked.connect(self.offline_slot)
self.manager.printSecondSignal.connect(self.print_onTextEdit)
def offline_slot(self):
self.do_some_calc_signal.emit()
I am building a small GUI application which runs a producer (worker) and the GUI consumes the output on demand and plots it (using pyqtgraph).
Since the producer is a blocking function (takes a while to run), I (supposedly) moved it to its own thread.
When calling QThread.currentThreadId() from the producer it outputs the same number as the main GUI thread. So, the worker is executed first, and then all the plotting function calls are executed (because they are being queued on the same thread's event queue). How can I fix this?
Example run with partial:
gui thread id 140665453623104
worker thread id: 140665453623104
Here is my full code:
from PyQt4 import QtCore, QtGui
from PyQt4.QtCore import pyqtSignal
import pyqtgraph as pg
import numpy as np
from functools import partial
from Queue import Queue
import math
import sys
import time
class Worker(QtCore.QObject):
termino = pyqtSignal()
def __init__(self, q=None, parent=None):
super(Worker, self).__init__(parent)
self.q = q
def run(self, m=30000):
print('worker thread id: {}'.format(QtCore.QThread.currentThreadId()))
for x in xrange(m):
#y = math.sin(x)
y = x**2
time.sleep(0.001) # Weird, plotting stops if this is not present...
self.q.put((x,y,y))
print('Worker finished')
self.termino.emit()
class MainWindow(QtGui.QWidget):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.q = Queue()
self.termino = False
self.worker = Worker(self.q)
self.workerThread = None
self.btn = QtGui.QPushButton('Start worker')
self.pw = pg.PlotWidget(self)
pi = self.pw.getPlotItem()
pi.enableAutoRange('x', True)
pi.enableAutoRange('y', True)
self.ge1 = pi.plot(pen='y')
self.xs = []
self.ys = []
layout = QtGui.QVBoxLayout(self)
layout.addWidget(self.pw)
layout.addWidget(self.btn)
self.resize(400, 400)
def run(self):
self.workerThread = QtCore.QThread()
self.worker.moveToThread(self.workerThread)
self.worker.termino.connect(self.setTermino)
# moveToThread doesn't work here
self.btn.clicked.connect(partial(self.worker.run, 30000))
# moveToThread will work here
# assume def worker.run(self): instead of def worker.run(self, m=30000)
# self.btn.clicked.connect(self.worker.run)
self.btn.clicked.connect(self.graficar)
self.workerThread.start()
self.show()
def setTermino(self):
self.termino = True
def graficar(self):
if not self.q.empty():
e1,e2,ciclos = self.q.get()
self.xs.append(ciclos)
self.ys.append(e1)
self.ge1.setData(y=self.ys, x=self.xs)
if not self.termino:
QtCore.QTimer.singleShot(1, self.graficar)
if __name__ == '__main__':
app = QtGui.QApplication([])
window = MainWindow()
QtCore.QTimer.singleShot(0, window.run);
sys.exit(app.exec_())
The problem is that Qt attempts to choose the connection type (when you call signal.connect(slot)) based on the what thread the slot exists in. Because you have wrapped the slot in the QThread with partial, the slot you are connecting to resides in the MainThread (the GUI thread). You can override the connection type (as the second argument to connect() but that doesn't help because the method created by partial will always exist in the MainThread, and so setting the connection type to by Qt.QueuedConnection doesn't help.
The only way around this that I can see is to set up a relay signal, the sole purpose of which is to effectively change an emitted signal with no arguments (eg the clicked signal from a button) to a signal with one argument (your m parameter). This way you don't need to wrap the slot in the QThread with partial().
The code is below. I've created a signal with one argument (an int) called 'relay' in the main windows class. The button clicked signal is connected to a method within the main window class, and this method has a line of code which emits the custom signal I created. You can extend this method (relay_signal()) to get the integer to pass to the QThread as m (500 in this case), from where ever you like!
So here is the code:
from functools import partial
from Queue import Queue
import math
import sys
import time
class Worker(QtCore.QObject):
termino = pyqtSignal()
def __init__(self, q=None, parent=None):
super(Worker, self).__init__(parent)
self.q = q
def run(self, m=30000):
print('worker thread id: {}'.format(QtCore.QThread.currentThreadId()))
for x in xrange(m):
#y = math.sin(x)
y = x**2
#time.sleep(0.001) # Weird, plotting stops if this is not present...
self.q.put((x,y,y))
print('Worker finished')
self.termino.emit()
class MainWindow(QtGui.QWidget):
relay = pyqtSignal(int)
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.q = Queue()
self.termino = False
self.worker = Worker(self.q)
self.workerThread = None
self.btn = QtGui.QPushButton('Start worker')
self.pw = pg.PlotWidget(self)
pi = self.pw.getPlotItem()
pi.enableAutoRange('x', True)
pi.enableAutoRange('y', True)
self.ge1 = pi.plot(pen='y')
self.xs = []
self.ys = []
layout = QtGui.QVBoxLayout(self)
layout.addWidget(self.pw)
layout.addWidget(self.btn)
self.resize(400, 400)
def run(self):
self.workerThread = QtCore.QThread()
self.worker.termino.connect(self.setTermino)
self.worker.moveToThread(self.workerThread)
# moveToThread doesn't work here
# self.btn.clicked.connect(partial(self.worker.run, 30000))
# moveToThread will work here
# assume def worker.run(self): instead of def worker.run(self, m=30000)
#self.btn.clicked.connect(self.worker.run)
self.relay.connect(self.worker.run)
self.btn.clicked.connect(self.relay_signal)
self.btn.clicked.connect(self.graficar)
self.workerThread.start()
self.show()
def relay_signal(self):
self.relay.emit(500)
def setTermino(self):
self.termino = True
def graficar(self):
if not self.q.empty():
e1,e2,ciclos = self.q.get()
self.xs.append(ciclos)
self.ys.append(e1)
self.ge1.setData(y=self.ys, x=self.xs)
if not self.termino or not self.q.empty():
QtCore.QTimer.singleShot(1, self.graficar)
if __name__ == '__main__':
app = QtGui.QApplication([])
window = MainWindow()
QtCore.QTimer.singleShot(0, window.run);
sys.exit(app.exec_())
I also modified the graficar method to continue plotting (even after the thread is terminated) if there is still data in the queue. I think this might be why you needed the time.sleep in the QThread, which is now also removed.
Also regarding your comments in the code on where to place moveToThread, where it is now is correct. It should be before the call that connects the QThread slot to a signal, and the reason for this is discussed in this stack-overflow post: PyQt: Connecting a signal to a slot to start a background operation
I have the following two files:
import sys
import time
from PyQt4 import QtGui, QtCore
import btnModule
class WindowClass(QtGui.QWidget):
def __init__(self):
super(WindowClass, self).__init__()
self.dataLoaded = None
# Widgets
# Buttons
thread = WorkerForLoop(self.runLoop)
# thread.start()
self.playBtn = btnModule.playpauselBtnClass \
('Play', thread.start)
# Layout
layout = QtGui.QHBoxLayout()
layout.addWidget(self.playBtn)
self.setLayout(layout)
# Window Geometry
self.setGeometry(100, 100, 100, 100)
def waitToContinue(self):
print self.playBtn.text()
while (self.playBtn.text() != 'Pause'):
pass
def runLoop(self):
for ii in range(100):
self.waitToContinue()
print 'num so far: ', ii
time.sleep(0.5)
class WorkerForLoop(QtCore.QThread):
def __init__(self, function, *args, **kwargs):
super(WorkerForLoop, self).__init__()
self.function = function
self.args = args
self.kwargs = kwargs
def __del__(self):
self.wait()
def run(self):
print 'let"s run it'
self.function(*self.args, **self.kwargs)
return
if __name__ == '__main__':
app = QtGui.QApplication(sys.argv)
wmain = WindowClass()
wmain.show()
sys.exit(app.exec_())
and the second file btnModule.py:
from PyQt4 import QtGui, QtCore
class playpauselBtnClass(QtGui.QPushButton):
btnSgn = QtCore.pyqtSignal()
def __init__(self, btnName, onClickFunction):
super(playpauselBtnClass, self).__init__(btnName)
self.clicked.connect(self.btnPressed)
self.btnSgn.connect(onClickFunction)
def btnPressed(self):
if self.text() == 'Play':
self.setText('Pause')
self.btnSgn.emit()
print 'Changed to pause and emited signal'
elif self.text() == 'Pause':
self.setText('Continue')
print 'Changed to Continue'
elif self.text() == 'Continue':
self.setText('Pause')
print 'Changed to Pause'
If in the first file I remove the comment at thread.start() it works as expected, it starts the thread and then hangs until I click Play on the UI. However, I thought it should work even if I didn't start it there as the signal is btnSgn is connected to onClickFunction which in this case takes the value thread.start.
Used this as a reference
http://joplaete.wordpress.com/2010/07/21/threading-with-pyqt4/
I think the reason it doesn't work when you try to call thread.start() in your second file (via self.btnSgn.emit()) is that the thread object goes out of scope outside of the init function where you created it. So you are calling start() on an already deleted thread.
Just changing thread -> self.thread (i.e. making the thread object a member of the WindowClass object) works fine when I tried it, since thread is then kept alive till the end of the program.
I have a PySide (Qt) GUI which spawns multiple threads. The threads sometimes need to update the GUI. I have solved this in the following way:
class Signaller(QtCore.QObject) :
my_signal = QtCore.Signal(QListWidgetItem, QIcon)
signaller = Signaller()
class MyThread(threading.Thread):
def __init__(self):
super(IconThread, self).__init__()
# ...
def run(self) :
# ...
# Need to update the GUI
signaller.my_signal.emit(self.item, icon)
#
# MAIN WINDOW
#
class Main(QtGui.QMainWindow):
def __init__(self):
QtGui.QMainWindow.__init__(self)
# ...
# Connect signals
signaller.my_signal.connect(self.my_handler)
#QtCore.Slot(QListWidgetItem, QIcon)
def my_handler(self, item, icon):
item.setIcon(icon)
def do_something(self, address):
# ...
# Start new thread
my_thread = MyThread(newItem)
my_thread.start()
# ...
Is there an easier way? Creating the signals, handlers and connect them requires a few lines of code.
I started coding with PySide recently and I needed a equivalent of PyGObject's GLib.idle_add behaviour. I based the code off of your answer ( https://stackoverflow.com/a/11005204/1524507 ) but this one uses events instead of using a queue ourselves.
from PySide import QtCore
class InvokeEvent(QtCore.QEvent):
EVENT_TYPE = QtCore.QEvent.Type(QtCore.QEvent.registerEventType())
def __init__(self, fn, *args, **kwargs):
QtCore.QEvent.__init__(self, InvokeEvent.EVENT_TYPE)
self.fn = fn
self.args = args
self.kwargs = kwargs
class Invoker(QtCore.QObject):
def event(self, event):
event.fn(*event.args, **event.kwargs)
return True
_invoker = Invoker()
def invoke_in_main_thread(fn, *args, **kwargs):
QtCore.QCoreApplication.postEvent(_invoker,
InvokeEvent(fn, *args, **kwargs))
Which is used the same way in the above answer link.
This is what I have so far. I wrote the following code somewhere in a helper module:
from Queue import Queue
class Invoker(QObject):
def __init__(self):
super(Invoker, self).__init__()
self.queue = Queue()
def invoke(self, func, *args):
f = lambda: func(*args)
self.queue.put(f)
QMetaObject.invokeMethod(self, "handler", QtCore.Qt.QueuedConnection)
#Slot()
def handler(self):
f = self.queue.get()
f()
invoker = Invoker()
def invoke_in_main_thread(func, *args):
invoker.invoke(func,*args)
Then my threads can very easily run code to update the GUI in the main thread. There is no need to create and connect signals for every operation.
class MyThread(threading.Thread):
def __init__(self):
super(IconThread, self).__init__()
# ...
def run(self) :
# ...
# Need to update the GUI
invoke_in_main_thread(self.item.setIcon, icon)
I think something like this is quite nice.