multiprocessing deadlock

Gabriel Genellina gagsl-py2 at
Sat Oct 24 05:10:31 CEST 2009

En Thu, 22 Oct 2009 23:18:32 -0300, Brian Quinlan <brian at>  

I don't like a few things in the code:

> def _do(i):
>      print('Run:', i)
>      q = multiprocessing.Queue()
>      for j in range(30):
>          q.put(i*30+j)
>      processes = _make_some_processes(q)
>      while not q.empty():
>          pass

I'd use time.sleep(0.1) or something instead of this busy wait, but see  

> #    The deadlock only occurs on Mac OS X and only when these lines
> #    are commented out:
> #    for p in processes:
> #        p.join()

I don't know how multiprocessing deals with it, but if you don't join() a  
process it may become a zombie, so it's probably better to always join  
them. In that case I'd just remove the wait for q.empty() completely.

> for i in range(100):
>      _do(i)

Those lines should be guarded with: if __name__ == '__main__':

I don't know if fixing those things will fix your problem, but at least  
the code will look neater...

Gabriel Genellina

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