GUI is very sluggish using PyQt and Qthreads

Question

I have a problem with keeping a GUI responsive using PyQt and Qthreads. What I do is spawn a worker Qthread from the GUI which is cpu heavy. The worker Qthread sends a signal containing a numerical value in every cycle. In the GUI the signal is connected to an update function which takes the numerical value and repaints the GUI. I use the standard Qt SIGNAL/SLOT mechanism.

This all seems in line with documentation I've found online regarding PyQt, GUIs and Qthreads. The problem is that the worker thread triggers the signal so frequent, that the GUI becomes very sluggish. A solution would be to have the worker thread trigger the signal less frequent, but I would like to get a fast update of the progress.

This all seems very standard stuff, and yet I can't find a proper solution. Possibly I need to change the design?

Any help would be appreciated.

Code:

import calculator as ca

class GUI(QMainWindow):

    def __init__(self, config):
        QMainWindow.__init__(self)
        self.w_thread = WorkerThread()
        self.connect(self.w_thread, SIGNAL("update(PyQt_PyObject)"), self.update_gui)

    def start_calc(self):
        self.w_thread.start()

    def update_gui(self, progress_value):
        self.progress_value = progress_value
        self.repaint()

    def paintEvent(self, event):
        paint = QPainter()
        paint.begin(self)
        paint.drawText(300, 300, "progress: " + str(self.progress_value))
        paint.end()


class WorkerThread(QThread):

    def __init__(self):
        QThread.__init__(self)

    def __del__(self):
        self.wait()

    def run(self):
        ca.run_calculations(self)



*************** calculator.py ***************

def run_calculations(thread=None):

    while current_cycle < total_cycles:
        do_calculations()
        if current_cycle % 100 == 0:
            thread.emit(SIGNAL("update(PyQt_PyObject)"), current_progress_value)
        qApp.processEvents()
        current_cycle += 1

Can you be more clear about what in the GUI is sluggish (graphical updates, mouse interaction)? How long does your repaint function take? Is this running on a multi-core machine? — Luke
With sluggish I mean mouse interaction. Clicking on a buttom takes +/- 1 second to respond. Indeed, this is on a multi-core machine. As for the repaint, this signal from the worker thread calls a function from the main window, which executes 'self.repaint()' which triggers the main window paintEvent which redraws the numerical value (indicating the progress of the worker thread). — adfasdfsda
In general you should call update() instead of repaint(). This should lead to a performance boost in the case where your worker thread is sending signals faster than the GUI can respond to them. (see doc.qt.nokia.com/4.7/qwidget.html#repaint-6) — Luke

JAB JAB · Accepted Answer · 2011-07-08T16:53:28

A solution would be to have the worker thread trigger the signal less frequent, but I would like to get a fast update of the progress.

Because human reaction speed is much slower than the processing speed of a computer, this is the best, or at least the most likely to be simplest, solution. You can still get a "fast update of the progress" even if the GUI is only being repainted once every, say, 1/10th~1/30th of a second.

GUI is very sluggish using PyQt and Qthreads

2 Answers