I'm developing a python application that uses a C-extension module I also developed myself. The extension module does some heavy number crunching and makes use of OpenMP.
I was recently adding some GUI components to my Python application using PyQt4. However, when I show a window, the application crashes before the window is fully drawn (The window shows up very shortly). I was able to track the problem down: When I compile my number-crunching C-extension without OpenMP support the Window shows up fine and everything works. I guess it has something to do with the threading stuff between OpenMP and Qt. Has anyone ever made a similar observation?
Make sure that the OpenMP number crunching extension is free of race conditions.
Avoid updating windows or any other GUI operations from multiple threads - use #pragma omp single or #pragma omp master to this kind of stuff.
If you have a variable/callback to the python code, make sure that all threads have finished what they were supposed to before changing the variable or making the callback.

The threads from QT and the thread from OpenMP are completely different threads, so this shouldn't pose any problems.
Crash when showing a PyQt4 Window after importing a python extension that uses OpenMP