[PyKDE] PyQt4/win32 crash

[K.S.Sreeram]

Phil Thompson wrote:
> On Friday 15 September 2006 9:58 pm, K.S.Sreeram wrote:
>> [Qt-4.1.4, sip-4.4.5, PyQt-4.0.1, Python-2.4.3, MSVC-7.1]
>>
>> Hi all,
>>
>> I've been facing a random crash in my app for sometime, and i've got it
>> down to a simple test program. Run the attached script, click "Click Me"
>> and close the newly opened window, and it crashes!
>>
>> I used debug builds and poked around the code, and here's why i think
>> its crashing...
>>
>> The crash happens when a top-level window is closed, and all python
>> references to the window are lost in the 'closeEvent' method.
>>
>> When a window is closed using the close button at the right top of the
>> window, the Qt function "QWidgetPrivate::close_helper(mode)" gets called
>> with "mode == CloseWithSpontaneousEvent". This function is there in
>> src/gui/kernel/qwidget.cpp line 4609.
>>
>> In this function, close event is sent to the widget if mode is
>> CloseWithSpontaneousEvent, as in this case. By the time, the close event
>> is handled by the widget, the widget is already deleted because of
>> python's gc.
>>
>> The Qt code seems to check for this case using tests like
>> "that.isNull()". But on line 4642, the check for null is not performed
>> and the app crashes at that point.
>>
>> So this looks like it is a bug in Qt itself. But is there someway PyQt
>> can workaround this bug?
> 
> What if you swap the two lines of MyWindow.closeEvent()?

That doesn't help. The last python reference is actually the 'self'
parameter to the closeEvent. So the python gc kicks in only /after/ the
return from closeEvent.

As a workaround, i'm currently just planning to use a single shot timer
to keep a reference to the object until after the close fully completes.

[sreeram;]

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