Python Multiprocessing/threading Code Exits Early

I'm trying to create multiple processes which each call multiple threads. I'm running the following code with python3.5 A simplified example of the problem looks like this: import

Solution 1:

Resolution: the new bug was closed as a duplicate of http://bugs.python.org/issue18966

Alas, there's no simple, satisfying explanation "for why". The cause is that multiprocessing arranges for worker processes to leave Python via calling os._exit() rather than the normal sys.exit(). os._exit() skips all "normal" shutdown processing. Part of what's skipped is .join()-ing non-daemon threads, so the process just vanishes while the threads are still running.

That should at least (according to me) be documented, or preferably changed.

In the meantime, the workaround - as you already know - is to explicitly .join() the threads yourself.

ANOTHER WAY

Under Python 3.4 or later, you could also use multiprocessing's spawn start method:

https://docs.python.org/3/library/multiprocessing.html?highlight=spawn#contexts-and-start-methods

That causes worker processes to finish via sys.exit(exitcode), which does all the normal shutdown processing (including .join()-ing non-daemon threads).

spawn is the only start method available on Windows, which explains why I had no problem running your original example.