QThread, moveToThread and Thread ID

[Mika-L]

Dear all,

I am new to PyQt but I developed GUI apps in my past. I want to make a GUI in which a part is refreshed by a Thread. I tried to understand in the internet how it works and I made the following code (see below).

What I do :

• I create a "worker" class that inherits from QObject. From this worker class I print the threadID (QThread.currentThreadId())
• this worker is instanciated in the window object. It is run through a QThread after a moveToThread operation from the window.
• The worker sends signals to the window while it loops. The signal itself prints its threadID too
• I added a timer to the window to display again the threadID in which the window runs.

I obtain the same threadID in all the cases and I doubt my worker or my threadID display works well. Can you help ?

Here comes the code, and then the results.

Best Regards,
Mike

Code

#!/opt/miniconda3/bin/python3.7

from PyQt5.QtCore import QObject, QThread, pyqtSignal,QTimer
from PyQt5.QtWidgets import QApplication,QMainWindow
from time import sleep
import sys

class Worker(QObject):
    finished = pyqtSignal()
    progress = pyqtSignal()

    def run(self):
        """Long-running task."""
        while True:
            sleep(0.5)
            print("in Worker Thread : ", QThread.currentThreadId())
            self.progress.emit()
        self.finished.emit()

class Window(QMainWindow):
    def __init__(self,*args,**kwargs):
        super().__init__(*args,**kwargs)
        self.runLongTask()

    def workerProgress(self):
        print("Report Thread : ",QThread.currentThreadId())
        print("\n")


    def mainAppProgress(self):
        print("Timer Thread : ",QThread.currentThreadId())

    def runLongTask(self):
        # run the worker using a thread
        self.thread = QThread()
        self.worker = Worker()
        self.worker.moveToThread(self.thread)
        self.thread.started.connect(self.worker.run)
        self.worker.progress.connect(self.workerProgress)
        self.thread.start()

        # run a timer to display the window thread too
        self.timer = QTimer()
        self.timer.setInterval(500)
        self.timer.timeout.connect(self.mainAppProgress)
        self.timer.start()

app = QApplication(sys.argv)
win = Window()
win.show()
sys.exit(app.exec())

Results

Timer Thread :  <sip.voidptr object at 0x10079f0f0>
in Worker Thread :  <sip.voidptr object at 0x10079f0f0>
Report Thread :  <sip.voidptr object at 0x10079f0f0>


Timer Thread :  <sip.voidptr object at 0x10079f0f0>
in Worker Thread :  <sip.voidptr object at 0x10079f0f0>
Report Thread :  <sip.voidptr object at 0x10079f0f0>


Timer Thread :  <sip.voidptr object at 0x10079f0f0>
in Worker Thread :  <sip.voidptr object at 0x10079f0f0>
Report Thread :  <sip.voidptr object at 0x10079f0f0>


Timer Thread :  <sip.voidptr object at 0x10079f0f0>
in Worker Thread :  <sip.voidptr object at 0x10079f0f0>
Report Thread :  <sip.voidptr object at 0x10079f0f0>


Timer Thread :  <sip.voidptr object at 0x10079f0f0>
in Worker Thread :  <sip.voidptr object at 0x10079f0f0>
Report Thread :  <sip.voidptr object at 0x10079f0f0>


Timer Thread :  <sip.voidptr object at 0x10079f0f0>
in Worker Thread :  <sip.voidptr object at 0x10079f0f0>
Report Thread :  <sip.voidptr object at 0x10079f120>

[eyllanesc]

@Mika-L What you are printing is the python object, if you want to get the id of the thread then use int():

int(QThread.currentThreadId())

Output:

in Worker Thread :  140448685921856
Report Thread :  140448915945280


Timer Thread :  140448915945280
in Worker Thread :  140448685921856
Report Thread :  140448915945280


Timer Thread :  140448915945280
in Worker Thread :  140448685921856
Report Thread :  140448915945280

If you want to check if the function is executed in the main thread then compare the QThread.currentThread() with QCoreApplication.instance().thread():

print("is executed main thread?",  QThread.currentThread() is QCoreApplication.instance().thread())

Another alternative is to use the threading.current_thread() function:

Timer Thread :  <_MainThread(MainThread, started 140013290776384)>
in Worker Thread :  <_DummyThread(Dummy-1, started daemon 140013060752960)>
Report Thread :  <_MainThread(MainThread, started 140013290776384)>


Timer Thread :  <_MainThread(MainThread, started 140013290776384)>
in Worker Thread :  <_DummyThread(Dummy-1, started daemon 140013060752960)>
Report Thread :  <_MainThread(MainThread, started 140013290776384)>

[Mika-L]

@eyllanesc : very very nice answer ! thanks a lot ! That really helps !

I have a last question : is there somewhere a tool to display the CPU consumption for a given thread, cross-platform ? Or a pythonic tool ?

Thanks again,
Mike