multiprocessing: apply_async with different callbacks

André Panisson panisson at
Tue Jul 17 23:44:27 CEST 2012

Hi all,

I'm having a strange behavior when executing the following script:
import multiprocessing

def f(i):
     return i

p = multiprocessing.Pool()
for i in range(20):
     def c(r):
         print r, i
     p.apply_async(f, (i,) , callback=c)

0 6
1 11
2 13
3 15
4 15
5 19

It seems that the callbacks of all submitted tasks are being overridden 
with the last callback submitted by apply_async.
Is this the right behaviour or I am stumbling in some issue? I'm using 
Python 2.7.3 @ Ubuntu 12.04


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