[vtk-developers] InvokeEvent test randomly failing quiz

[David Gobbi]

I wasn't able to reproduce the issue, but I think that I found out what
causes it.  When vtkPythonCommand::Execute() is called, it tries to promote
the subject object (i.e. the object being deleted for DeleteEvent) into a
Python object.  I was able to confirm that this actually happens, and even
though I couldn't get it to crash, I'm pretty sure that it puts the program
into a bad state.

See https://gitlab.kitware.com/vtk/vtk/merge_requests/2131

 - David

On Tue, Nov 1, 2016 at 9:19 AM, Utkarsh Ayachit <utkarsh.ayachit at kitware.com
> wrote:

> Ken,
>
> The issue seems to be that the callback is attempted to be called for
> vtkCommand::DeleteEvent since the observer is set to respond to
> "AnyEvent".  When the object is being cleaned up as part of the
> interpreter being destroyed, calling Python commands is indeed
> problematic and hence the failure.
>
> The test can be fixed by changing the observer to only listen to
> ModifiedEvent instead of AnyEvent. Ideally vtkPythonCommand::Execute
> can check if the interpreter is being cleaned up, but I am not sure
> how to do that.
>
> Utkarsh
>
> On Tue, Nov 1, 2016 at 10:33 AM, Ken Martin <ken.martin at kitware.com>
> wrote:
> > OK here is a puzzle. We have a test that is occasionally failing and I
> > suspect it fails due to random python order of deletion of vtk objects.
> The
> > relevant python code is below. It fails when unregistering a vtkObject
> and I
> > suspect it is failing when invoking an callback during the
> > unregisterinternal method see the stack trace. So maybe python has
> deleted
> > the object from its maps but then it gets used in a callback for another
> > object being deleted? Again my python foo is weak but maybe we have to
> > unregister the anyEvent observer before the end of the script? Maybe
> > something else?
> >
> >     @vtk.calldata_type(vtk.VTK_OBJECT)
> >     def callbackObj(self, caller, event, calldata):
> >         self.calldata = calldata
> >
> >     def setUp(self):
> >         self.vtkObj = vtk.vtkObject()
> >
> >         self.vtkObjForCallData = vtk.vtkObject()
> >
> >     def test_obj(self):
> >         self.vtkObj.AddObserver(vtk.vtkCommand.AnyEvent,
> self.callbackObj)
> >         self.vtkObj.InvokeEvent(vtk.vtkCommand.ModifiedEvent,
> > self.vtkObjForCallData)
> >         self.assertEqual(self.calldata, self.vtkObjForCallData)
> >
> > 0x7f98bd3e8770 : ??? [(???) ???:-1]
> > 0x7f98bd19b778 : vtkPythonCommand::Execute(vtkObject*, unsigned long,
> void*)
> > [(libvtkWrappingPython35Core-7.1.so.1) ???:-1]
> > 0x7f98bcb9fd7e : ??? [(???) ???:-1]
> > 0x7f98bcba000c : vtkObject::UnRegisterInternal(vtkObjectBase*, int)
> > [(libvtkCommonCore-7.1.so.1) ???:-1]
> > 0x7f98bd19f045 : vtkPythonUtil::RemoveObjectFromMap(_object*)
> > [(libvtkWrappingPython35Core-7.1.so.1) ???:-1]
> > 0x7f98bd1a5b30 : PyVTKObject_Delete [(libvtkWrappingPython35Core-
> 7.1.so.1)
> > ???:-1]
>
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