How to check for threads being finished?

Stefan Behnel stefan_ml at
Sat Jul 6 10:49:00 CEST 2013

Irmen de Jong, 05.07.2013 19:12:
> On 5-7-2013 18:59, Steven D'Aprano wrote:
>> I then block until the threads are all done:
>> while any(t.isAlive() for t in threads):
>>     pass
>> Is that the right way to wait for the threads to be done? Should I stick 
>> a call to time.sleep() inside the while loop? If so, how long should I 
>> sleep? That's probably an unanswerable question, but some guidelines on 
>> choosing the sleep time will be appreciated.
> I think your while loop busy-waits until the threads are completed.
> Do this instead:
> for t in threads: t.join()    # optionally pass a timeout to join

A related stdlib tool that many people don't seem to know is the thread
pool in concurrent.futures. It supports both waiting for all threads to
finish as well as iterating over results as they come in. It also comes
with a parallel map() implementation.

New in Py3.2, but there's also a backport AFAIR.


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