[PyQt] assertion failure in sip

Phil Thompson phil at riverbankcomputing.com
Sat Sep 17 04:51:42 BST 2011

On Fri, 16 Sep 2011 22:28:24 +0200, Erik Janssens
<Erik.Janssens at conceptive.be> wrote:
> Hi,
> I'm seeing an assertion failure in sip, stacktrace
> attached.
> It happens consistently, but only after long stress
> tests of a large application.
> Any suggestions on what might be causing this
> failure, so I can try to isolate the case ?

It looks like there might be a race condition when the Python object
wrapping the QWidget is being garbage collected and the QWidget itself is
still calling it's virtual methods.

This is supposed to be taken care of by the "if (sipSelf == NULL)" test
earlier in the function. This test is done without the GIL. The pointer
being tested is set in dealloc_QWidget() (with the GIL).

Therefore if the Python object is in the process of being garbage
collected but before dealloc_QWidget() gets a chance to reset the pointer,
and then QWidget::changeEvent() gets called then there might be a problem.

The fix would be to do the test with the GIL but that requires a change to
the signature of sip_api_is_py_method() to pass a pointer to the pointer
being tested rather than the pointer itself.

Watch this space...


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