[vtkusers] Why does deletion of vtkpolydatamapper cause an infinite loop in vtkclearopenglerrors?

[Adam Bruss]

Hello,
We have a WinForms c++/cli CAD based application that uses VTK 6.1. One of the application's features is playing a script which plays back operations the user had previously done interactively. We pop a modal progress form while the script is playing and do the non-ui work of the script in a background thread. Part of the work of the background thread is creating and deleting vtkPolyDataMappers. While the background thread is going and the progress form is showing we need to update a display in the main thread by calling vtkWin32RenderWindowInteractor::Render().
We have a timer setup so Render is called every few hundred milliseconds at most in a UserControl::OnPaint event handler. This allows the view to update while the script is playing giving the user feedback.
This used to work in VTK 5. But now an infinite loop happens upon deletion of a vtkPolyDataMapper in the background thread. The infinite loop is in vtkClearOpenGLErrors:
void vtkClearOpenGLErrors()
{
while (glGetError()!=GL_NO_ERROR){;}
}
Inside the vtkpolydatamapper is a vtkOpenGLDisplayListPainter. When this gets deleted by vtkGarbageCollectorImpl::CollectInternal we get stuck in vtkClearOpenGLErrors.
Does anyone have experience with VTK and threading that could help? Do you know anything about this? It's only an apparent problem in VTK 6.1. Is it illegal to have the main UI thread calling Render on a vtkWin32RenderWindowInteractor while a background thread is doing deletes on a vtkPolyDataMapper? It isn't a timing issue. I think it might be an OpenGL context issue but not sure how to fix it. The problem does go away if we avoid calling Render on the display while the background thread is going but we'd like to give the user feedback while the script is playing.
Thanks,
Adam

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