PyQt6 - long running thread - QThread, QTimer or QRunnable?

[bashtian]

Hello,
I am facing an issue and I need some help please.
I have an app, that need a process in background to listen to a websocket and await for commands.
What would you recommend to do to run a task in background for as long as the app is running please ?

Originally I had it in a QTimer as follow:

class Controller(...):
    # [...]
    def start_background_process(self):
        self.timer = QTimer(QApplication.instance())
        self.timer.timeout.connect(self.websocket_connector.handle)
        self.timer.start(100)  # pause a bit to avoid too much CPU usage

class WSConnector(...):
    # [...]
    def handle(self):
        ready_to_read, ready_to_write, in_error = \
            select.select((self.socket_handler.websocket.sock,), (), (), 0)
        while ready_to_read:
            # Do the job

This was working more or less ok, until I added some windows and I notice that the UI was lagging/not working while the process was doing some stuff. Altho it was handling the QApplication.instance().quit() very nicely and kill that timer.

As a results I switched to QRunnable worker model with a QThreadpool and a while True to keep the worker alive. It solved the freezing UI - Yayyyh ! But I don't like very much as it adds complexity and it makes it hard to kill when the app needs to quit:

class Controller(...):
    def __init__(self, ...):
        self.threadpool = QThreadPool()
        # [...]
    
    def start_background_process(self):
        self.worker = Worker(self.websocket_connector.handle)
        self.threadpool.start(self.worker)

class WSConnector(...):
    # [...]
    def handle(self):
        while True:  # adds more complexity but required to keep the thread alive :(
            ready_to_read, ready_to_write, in_error = \
                select.select((self.socket_handler.websocket.sock,), (), (), 0)
            while ready_to_read:
                # Do the job
            time.sleep(0.1)  # pause a bit to avoid too much CPU usage

[SGaist]

Hi,

Since Qt has the QWebSocket class that is asynchronous, why not use it and stop adding threads to your application ?

[bashtian]

Hi @SGaist !
Thanks for the info!
I will take a look, that sounds interesting to dig into it but it also looks like a lot of work to rework my lib that handle this particular socket app and I would be locked to Qt then :(

[bashtian]

It actually wasnt that much of a problem to map the QtWebSocket over my API. thanks again for the hint !