[vtk-developers] InvokeEvent test randomly failing quiz

[David Gobbi]

Okay, I think that I've found the problem.  The crash occurs when there is
a mismatch between the calldata_type set for the callback, and the type of
the actual calldata object passed at event invocation.

In TestInvokeEvent.py, when the DeleteEvent is invoked, the calldata is a
vtkObject, so when the callback has been set to expect something else,
there's a crash.  In other words, the test crashes simply because the
callbacks are receiving events that the test's author didn't anticipate.

So Ken's earlier MR that modified the test is probably going in the right
direction.  Since the callbacks in that test are expecting specific
calldata types, they should be made to observe only the specific events
that they expect.

I also think that TestInvokeEvent.py shouldn't use ModifiedEvent as the
event to watch for.  For each calldata type, it should use an event type
that usually uses calldata of that type.

For reference:
https://gitlab.kitware.com/vtk/vtk/merge_requests/2135

 - David

On Wed, Nov 2, 2016 at 2:48 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> It looks like the fix didn't work.  But now that I know which dashboard is
> failing, and have seen the whole stack trace, I have a better idea of where
> the problem might be.  I'll give it another shot tonight.
>
>  - David
>
> On Tue, Nov 1, 2016 at 11:48 PM, David Gobbi <david.gobbi at gmail.com>
> wrote:
>
>> 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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