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How to check for threads being finished?

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  How to check for threads being finished? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-05 16:59 +0000
    Re: How to check for threads being finished? Chris Angelico <rosuav@gmail.com> - 2013-07-06 03:11 +1000
    Re: How to check for threads being finished? Irmen de Jong <irmen.NOSPAM@xs4all.nl> - 2013-07-05 19:12 +0200
      Re: How to check for threads being finished? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-06 02:18 +0000
      Re: How to check for threads being finished? Stefan Behnel <stefan_ml@behnel.de> - 2013-07-06 10:49 +0200
    Re: How to check for threads being finished? Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-05 11:18 -0600
    Re: How to check for threads being finished? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-07-05 16:13 -0400
    Re: How to check for threads being finished? Cameron Simpson <cs@zip.com.au> - 2013-07-06 10:45 +1000

#50003 — How to check for threads being finished?

I have a pool of worker threads, created like this:

threads = [MyThread(*args) for i in range(numthreads)]
for t in threads:
    t.start()


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.




-- 
Steven

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#50004

On Sat, Jul 6, 2013 at 2:59 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> I then block until the threads are all done:
>
> while any(t.isAlive() for t in threads):
>     pass
>

Using the threading module, I assume. Is there any reason you can't
simply join() each thread in succession?

ChrisA

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#50005

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


-Irmen

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#50038

On Fri, 05 Jul 2013 19:12:44 +0200, Irmen de Jong wrote:

> 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

Yes, the busy-wait was what I was concerned about.

Thanks to everyone who suggested the same solution.




-- 
Steven

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#50055

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.

http://docs.python.org/3/library/concurrent.futures.html#threadpoolexecutor-example

http://docs.python.org/3/library/concurrent.futures.html#module-functions

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

Stefan

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#50006

On Fri, Jul 5, 2013 at 10:59 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> I have a pool of worker threads, created like this:
>
> threads = [MyThread(*args) for i in range(numthreads)]
> for t in threads:
>     t.start()
>
>
> 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.

for thread in threads:
    thread.join()

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#50018

On 05 Jul 2013 16:59:54 GMT, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> declaimed the following:

>I have a pool of worker threads, created like this:
>
>threads = [MyThread(*args) for i in range(numthreads)]
>for t in threads:
>    t.start()
>
>
>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.

	If you are just going to wait for them to finish, and never use them
again...

for t in threads:
	t.join()

	Doesn't matter which thread ends first, this operation will either
block if the thread hasn't finished or cycle to the next thread if it has.
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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#50031

On 05Jul2013 16:59, Steven D'Aprano <steve+comp.lang.python@pearwood.info> wrote:
| I have a pool of worker threads, created like this:
| 
| threads = [MyThread(*args) for i in range(numthreads)]
| for t in threads:
|     t.start()
| 
| I then block until the threads are all done:
| 
| while any(t.isAlive() for t in threads):
|     pass

This spins.

How about:

  for t in threads:
    t.join()

Blocks instead of polls.

Cheers,
-- 
Cameron Simpson <cs@zip.com.au>

Processes are like potatoes.    - NCR device driver manual

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