> I think this is indeed useful, but I'm tempted to go further and say we 
> should make this the default - and only - behavior. This will probably 
> break existing code that accidentaly relied the fact that the 
> implementation uses a bare fork(), but i'd say it's worth it:

I'm not convinced about making it the default behaviour, and certainly not the only one.

I have a working patch which ensures that leaked semaphores get cleaned up on exit.  However, I think to add proper tests for the patch, test_multiprocessing needs to be refactored.  Maybe we could end up with

multiprocessing_common.py
test_multiprocessing_processes_fork.py
test_multiprocessing_processes_nofork.py
test_multiprocessing_manager_fork.py
test_multiprocessing_manager_nofork.py
test_multiprocessing_threads.py
test_multiprocessing_others.py

The actual unittests would be in multiprocessing_common.py and test_multiprocessing_others.py.  The other files would run the unittests in multiprocessing_common.py using different configurations.

Thoughts?