[PyQt] CPU spin and an error when using QQuickPaintedItem

[Russell Warren]

As a small follow-up, the same exact CPU spinning problem (and the
presumably related QObject::killTimer message) also happen when run on
Windows with python 3.5.2 (Anaconda 4.1.1 64-bit) with the PyQt 5.7.0 wheel.


On Sat, Nov 19, 2016 at 7:32 PM, Russell Warren <russ at perspexis.com> wrote:

> Sorry... This is on 64 bit Linux with the latest version from pypi at this
> moment.
>
> On Nov 19, 2016 6:31 PM, "Russell Warren" <russ at perspexis.com> wrote:
>
>> I'm having a CPU-spinning problem, together with an odd
>> QObject::killTimer error, with a basic use case of QQuickPaintedItem.
>>
>> I've reduced the example down so that the meat of it is just this:
>>
>> 1. Create a QGraphicsScene with some QGraphicsItems in it
>> 2. Create a QQuickPaintedItem to render the scene to QML
>> 3. Call QGraphicsScene.render(painter) inside the .paint of
>> QQuickPaintedItem
>>
>> When I do this, it superficially works as I want, but I get an error to
>> stdout, and the CPU spins to 100%. Using strace it can be seen that the CPU
>> is spinning on a poll(), like seen in this capture:
>>
>> https://i.snag.gy/I6QZvH.jpg
>>
>> The FDs being polled are a socket and an 'anon_inode:[eventfd]', which is
>> (I think) the normal Qt event loop.
>>
>> The error that results is this:
>>
>>     $ python HeatMapProblem.py
>>     QObject::killTimer: Timers cannot be stopped from another thread
>>
>> This timer problem is probably related, because the spinning is likely
>> what would happen with a zero timeout timer.
>>
>> Everything *seems* like it is being done correctly from the Qt side of
>> things. Is there something wrong I'm doing with PyQt?
>>
>> Basic code below (two files... heatmap.qml and HeatMapProblem.py).
>>
>> Thanks,
>> Russ
>>
>> #####
>> ### heatmap.qml
>> #####
>>
>> import QtQuick 2.0
>> import QtQuick.Window 2.2
>> import Heatmap 1.0
>>
>> Window {
>>     visible: true
>>     width: 500
>>     height: 500
>>     MyHeatmap {
>>         anchors.fill: parent
>>     }
>> }
>>
>> #####
>> ### HeatMapProblem.py
>> #####
>> #!/usr/bin/env python
>> import random
>>
>> from OpenGL import GL   # workaround for Nvidia issue on linux (see
>> http://goo.gl/pGPgVz)
>> import PyQt5.QtWidgets as QtWidgets
>> from PyQt5.QtQuick import QQuickItem, QQuickPaintedItem, QQuickView
>> import PyQt5.QtCore as QtCore
>> import PyQt5.QtGui as QtGui
>> import PyQt5.QtQml as QtQml
>>
>> class MyPolygon(QtWidgets.QGraphicsPolygonItem):
>>     def __init__(self, PolyPoints, parent = None):
>>         super(MyPolygon, self).__init__(PolyPoints, parent)
>>         color = QtGui.QColor(*(random.randint(0, 128) for x in range(3)))
>>         self.setBrush(QtGui.QBrush(color))
>>
>> class MyScene(QtWidgets.QGraphicsScene):
>>     def __init__(self, parent=None):
>>         super(MyScene, self).__init__(parent)
>>         blackPen = QtGui.QPen(QtCore.Qt.black, 1)
>>         blackPen.setCosmetic(True)
>>
>>         numWide = numHigh = 3
>>         boxes = []
>>         for x in range(numWide):
>>             for y in range(numHigh):
>>                 bl = (x*10,      y*10)
>>                 tl = (x*10     , y*10 + 10)
>>                 tr = (x*10 + 10, y*10 + 10)
>>                 br = (x*10 + 10, y*10)
>>                 polyDef = [bl, tl, tr, br, bl]
>>                 poly = QtGui.QPolygonF([QtCore.QPointF(x, y) for (x, y)
>> in polyDef])
>>                 item = MyPolygon(poly, parent = None)
>>                 item.setPen(blackPen) #polygon border
>>                 self.addItem(item)
>>
>> class MyQMLScene(QQuickPaintedItem):
>>     def __init__(self, parent = None):
>>         super(MyQMLScene, self).__init__(parent)
>>         self._Scene = MyScene(parent = self)
>>
>>     def paint(self, painter):
>>         self._Scene.render(painter)  # NOTE: comment this out and no
>> problems exist!
>>         pass
>>
>> if __name__ == '__main__':
>>     import sys
>>     app = QtWidgets.QApplication(sys.argv)
>>     QtQml.qmlRegisterType(MyQMLScene, "Heatmap", 1, 0, "MyHeatmap")
>>     engine = QtQml.QQmlApplicationEngine()
>>     engine.load("heatmap.qml")
>>     sys.exit(app.exec_())
>>
>>
>>
>>


-- 
Russell Warren
Perspexis Technologies Inc.

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