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IDProjectCategoryView StatusDate SubmittedLast Update
0015545VTK(No Category)public2015-06-16 14:202016-08-12 09:55
ReporterEdson Tadeu M. Manoel 
Assigned ToKitware Robot 
PriorityhighSeverityminorReproducibilityalways
StatusclosedResolutionmoved 
PlatformOSOS Version
Product Version6.0.0 
Target VersionFixed in Version 
ProjectTBD
Typecrash
Summary0015545: Observer crashes with Python thread, bug in vtkPythonCommand and also in dataset_adapter
Description  Currently, if an observer is added in a python thread and then executed in another thread after the first one has finished, it will cause a segfault/access violation in the python interpreter.

  This code reproduces the problem:


    from Queue import Queue
    from threading import Thread
    import vtk
    
    
    def on_delete(caller, event):
        print 'on_delete:'
        print ' caller:', caller
        print ' event:', event
    
    
    def create_object_with_observer(result_queue):
        object_with_observer = vtk.vtkObject()
        object_with_observer.AddObserver('DeleteEvent', on_delete)
    
        result_queue.put(object_with_observer)
    
    
    def test_observer_command_with_threads():
        result_queue = Queue()
    
        thread = Thread(target=create_object_with_observer, args=(result_queue,))
        thread.start()
        thread.join()
    
        object_with_observer = result_queue.get(block=True)
        print object_with_observer
        del object_with_observer # <-- crashes here
        print 'checkpoint'
    
    
    if __name__ == '__main__':
        test_observer_command_with_threads()


This seems to happen because of this line in vtkPythonCommand.cxx, which seems to be assigning a bad ThreadState pointer to _PyThreadState_Current:


    prevThreadState = PyThreadState_Swap(this->ThreadState);


(The pointer seems to be dangling. Perhaps vtkPythonCommand::SetThreadState should incref the PyThreadState* object?)

This bug is directly affecting dataset_adapter, because it causes a crash in this use case (dataset_adapter uses a command to store the numpy array ref):


    from Queue import Queue
    from threading import Thread
    from vtk.numpy_interface.dataset_adapter import UnstructuredGrid
    import numpy
    import vtk
    
    
    def create_unstructured_grid(result_queue):
        points = numpy.array([[0.0, 0.0, 0.0]])
        ug = UnstructuredGrid(vtk.vtkUnstructuredGrid())
        ug.SetPoints(points)
        result_queue.put(ug)
    
    
    def test_unstructured_grid_in_thread():
        result_queue = Queue()
        thread1 = Thread(target=create_unstructured_grid, args=(result_queue,))
        thread1.start()
        thread1.join()
        ug = result_queue.get(block=True)
        print ug
        del ug # <-- crashes
        print 'checkpoint'
    
    
    if __name__ == '__main__':
        test_unstructured_grid_in_thread()
Steps To ReproduceI was able to reproduce the problem with the supplied test program.

Also, I replaced the DeleteEvent with UserEvent, and it still crashed:

    print object_with_observer
    object_with_observer.InvokeEvent(vtk.vtkCommand.UserEvent) # <-- crashes here
    print 'checkpoint'

Crash occurred in vtkPythonCommand.cxx line 222:

       219 arglist = Py_BuildValue((char*)"(Ns)", obj2, eventname);
       220 }
       221
    -> 222 PyObject *result = PyEval_CallObject(this->obj, arglist);
       223 Py_DECREF(arglist);
       224
       225 if (result)
Additional Information
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Issue History
Date ModifiedUsernameFieldChange
2015-06-16 14:20Edson Tadeu M. ManoelNew Issue
2015-06-17 10:01David GobbiReproducibilityhave not tried => always
2015-06-17 10:01David GobbiSteps to Reproduce Updatedbug_revision_view_page.php?rev_id=1116#r1116
2016-07-06 16:47Berk GeveciStatusbacklog => expired
2016-08-12 09:55Kitware RobotNote Added: 0037395
2016-08-12 09:55Kitware RobotStatusexpired => closed
2016-08-12 09:55Kitware RobotResolutionopen => moved
2016-08-12 09:55Kitware RobotAssigned To => Kitware Robot

Notes
(0037395)
Kitware Robot   
2016-08-12 09:55   
Resolving issue as `moved`.

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