Python 3.4: PyQt on Windows: Crash on exit only on some computers

Question

I have a Python program that I packaged with cx_freeze to make executable. The program is strictly a desktop program for data acquisition. It works fine and exits fine on every computer, but on one desktop of one of our collaborators with Windows 7 on it, it crashes only on exit (I emphasize that no pythonic errors are given. Just a low-level crash with zero information about it). Simply starting and exiting the program crashes it!

I got the guy to create a memory dump for me, and he did. The weird part is the following: Creating a memory dump out of this and analyzing it with WinDbg gives the following chain of errors:

STACK_TEXT:  
WARNING: Stack unwind information not available. Following frames may be wrong.
0020f940 5c51b34e 5c7bd640 9d7a3385 03c93748 QtCore4!QHashData::free_helper+0x26
0020f974 76e314bd 00b30000 00000000 03e0c4c0 QtGui4!QGestureRecognizer::reset+0x1f9e
0020f9a0 5c51c968 03c93748 5d3608c2 00000001 kernel32!HeapFree+0x14
0020f9a8 5d3608c2 00000001 03c93748 03891250 QtGui4!QGestureRecognizer::reset+0x35b8
0020f9c0 5d3627b5 9d0dae1c 03891250 03cac0a0 QtCore4!QObjectPrivate::deleteChildren+0x72
00000000 00000000 00000000 00000000 00000000 QtCore4!QObject::~QObject+0x3e5

Now what surprises me is that a complaint from QGestureRecognizer (which is a part of QtGUI apparently) is given! But why? I don't use any touch capabilities! The modules I use are: QtCore and QtGUI. Where is this coming from? Can I, like, force disable everything related to that class: QGestureRecognizer? What would you do in this case?

Update:

This issue seems to happen ONLY on Windows 7 computers. It was tested on 2 computers with Windows 7 and the same crash happened.

AdrienW · Accepted Answer · 2016-07-26 14:29:22Z

1

It seems to have trouble freeing memory. You could try to do it manually with some function like this:

def clean(item):
    """Clean up the memory by closing and deleting the item if possible."""
    if isinstance(item, list) or isinstance(item, dict):
        for _ in range(len(item)):
            clean(list(item).pop())
    else:
        try:
            item.close()
        except (RuntimeError, AttributeError): # deleted or no close method
            try:
                item.deleteLater()
            except (RuntimeError, AttributeError): # deleted or no deleteLater method
                pass

Then you define a cleaning method in your main widget.

class MyWindow(QWidget):
    def cleanUp(self):
        # Clean up everything
        for i in self.__dict__:
            item = self.__dict__[i]
            clean(item)

Finally, before calling qt_app._exec(), you'll have to connect like this:

qt_app.aboutToQuit.connect(app.cleanUp)

where app is your main window.

EDIT:

Wrapping everything under the if __name__ == '__main__' line into a single main() function works sometimes, but I have no idea why.

edited Jul 26, 2016 at 14:29

answered Jul 26, 2016 at 12:53

AdrienW

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5 Comments

The Quantum Physicist Over a year ago

Thanks. I'll try this and report :)

The Quantum Physicist Over a year ago

I implemented the solution... works on my computer, but doesn't work on the computer with the problem... it still crashes on exit.

The Quantum Physicist Over a year ago

I already have that... everything is under if __name__ == '__main__':. The only thing not in that is a single import.

AdrienW Over a year ago

Then I must admit I don't know, I don't have enough elements to give you the answer. This post may help others with a similar problem though, so I'll leave it here

The Quantum Physicist Over a year ago

Absolutely. Please keep it as it's useful anyway :) . Thanks for trying to help.

The Quantum Physicist · Accepted Answer · 2016-10-18 14:07:40Z

0

It turned out that ALL the problems I used to have with this program crashing were because of QThread (on Windows). All the users I know of that used QThread on Windows got similar issues, and for some reason no one is fixing it.

Avoid QThread on Python. It's completely useless and more harmful than useful. I went now to multiprocessing. It's much better and isn't affected by GIL.

answered Oct 18, 2016 at 14:07

The Quantum Physicist

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