CODEWITHSUNDEEP
pythonqtsegmentation-faultpyside
Halsafar
Halsafar

Reputation: 2640

PySide Segfault on Shutdown

So I am getting a stack trace when my python qt app shutsdown. It is crashing when *iter is dereferenced. Here is the snippet from pyside basewrapper.cpp

static void decRefPyObjectList(const std::list<PyObject*>& lst, PyObject *skip)
{
    std::list<PyObject*>::const_iterator iter = lst.begin();
    while(iter != lst.end()) {
        if (*iter != skip) // causes segfault
            Py_DECREF(*iter);
        ++iter;
    }
}

From backtrace:

#0  0x00007f6ea2c22653 in Shiboken::decRefPyObjectList (lst=, skip=0x0) at debug/shiboken-1.2.2/libshiboken/basewrapper.cpp:595
#1  0x00007f6ea2c24e44 in Shiboken::Object::clearReferences (self=0x7f6e7260c908) at debug/shiboken-1.2.2/libshiboken/basewrapper.cpp:1361
#2  0x00007f6ea2c23f86 in Shiboken::Object::destroy (self=0x7f6e7260c908, cppData=0x7f6e540f1220) at debug/shiboken-1.2.2/libshiboken/basewrapper.cpp:1127
#3  0x00007f6ea0f29d4f in QDataWidgetMapperWrapper::~QDataWidgetMapperWrapper (this=0x7f6e540f1220, __in_chrg=<optimized out>) at debug/pyside-qt4.8+1.2.2/build/PySide/QtGui/PySide/QtGui/qdatawidgetmapper_wrapper.cpp:309

Any tips on what situation might cause this? From reviewing the stack trace it is happening during QT/PySide tear down. When it goes to clean up all the object references.

Upvotes: 3

Views: 593

Answers (1)

Halsafar
Halsafar

Reputation: 2640

It turns out that Python garbage collector was grabbing the reference and then PySide was trying to clean up the same reference.

The solution was to explicitly hold a reference to said object in python. In our case it was a model we attached to QT.

Within a class that subclasses QDataWidgetMapper. This breaks, model is the offender, it is not stored outside the mapper meaning it is a loose reference for the GC to pick up:

def setModel(self, model):
        QDataWidgetMapper.setModel(self, model)

Change to:

def setModel(self, model):
        self._model = model
        QDataWidgetMapper.setModel(self, model)

Now we are storing explicitly a reference to model, it won't get garbage collected and PySide can clean it up.

Upvotes: 2

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