Not sure if I'm using QThread properly

Tauri

Hello,

I'm using qml as my front end, and I connect it using signals and slots to the backend.
I have some data that I'm processing after selecting a file and my ui is frozen until that process is complete which is why I wanted to try and solve that using QThread.

This is a simplified version of how I'm currently using it and it's not working for me (ui still frozen):

from functools import partial

class Secondary(QObject):
    update_list = Signal()

    def __init__(self):
        QObject.__init__(self)

    def process_data(self, file):
        do stuff
        self.update_list.emit()


class Main(QObject):

    def __init__(self):
        QObject.__init__(self)
        self.m_thread = QThread(self)
        self.m_thread.start()
        self.secondary = Secondary()
        self.secondary.moveToThread(self.m_thread)
        self.secondary.update_list.connect(method_to_update_list)
        
    @Slot()
    def load_file(self):
        wrapper = partial(self.secondary.process_data, file)
        QTimer.singleShot(0, wrapper)

The "load_file" method is called from the ui, and then the ui is frozen until "process_data" in the Secondary class is complete.
What am I missing? Or am I just not using it correctly at all?

Thanks in advance

SGaist

Add a signal to your MainWindow class, connect it to your worker object slot and emit it when appropriate.

SGaist

Hi,

I am guessing that the "partial" short circuits the Qt connection detection and thus the slot is called in the main thread context.

Tauri

Hi @SGaist,

I tried replacing the partial with either:

QTimer.singleShot(0, self.secondary, SLOT(self.secondary.process_data(file)))

Which runs successfully but gives me the following:
RuntimeWarning: MetaObjectBuilder::addMethod: Invalid method signature provided for ""
QTimer.singleShot(0, self.secondary, SLOT(self.secondary.process_data(file)))
qt.core.qobject.connect: QObject::connect: Parentheses expected, slot Secondary::

Not sure exactly what it means or what I should do to avoid it.

Or:

QTimer.singleShot(0, lambda : self.secondary.process_data(file))

Both work but the ui is still frozen just like when I was using partial, so I'm kinda lost as to why this is not working.

SGaist

Add a signal to your MainWindow class, connect it to your worker object slot and emit it when appropriate.

Tauri

@SGaist Thanks!
I implemented Signal/Slot like you suggested and it's working great now without even needing QTimer.