CODEWITHSUNDEEP
pythonpython-2.7poolmultiprocess
hercules.cosmos
hercules.cosmos

Reputation: 275

python multiprocessing freezing

I am trying to implement multiprocessing with Python. It works when pooling very quick tasks, however, freezes when pooling longer tasks. See my example below: 

from multiprocessing import Pool
import math
import time

def iter_count(addition):
    print "starting ", addition
    for i in range(1,99999999+addition):
        if i==99999999:  
            print "completed ", addition
            break

if __name__ == '__main__':
    print "starting pooling "
    pool = Pool(processes=2)
    time_start = time.time()
    possibleFactors = range(1,3)   

    try: 
        pool.map( iter_count, possibleFactors)
    except:
        print "exception"

    pool.close()
    pool.join()      

    #iter_count(1)
    #iter_count(2)
    time_end = time.time()
    print "total loading time is : ", round(time_end-time_start, 4)," seconds"

In this example, if I use smaller numbers in for loop (something like 9999999) it works. But when running for 99999999 it freezes. I tried running two processes (iter_count(1) and iter_count(2)) in sequence, and it takes about 28 seconds, so not really a big task. But when I pool them it freezes. I know that there are some known bugs in python around multiprocessing, however, in my case, same code works for smaller sub tasks, but freezes for bigger ones.

Upvotes: 5

Views: 5324

Answers (1)

Tim Peters
Tim Peters

Reputation: 70735

You're using some version of Python 2 - we can tell because of how print is spelled.

So range(1,99999999+addition) is creating a gigantic list, with at least 100 million integers. And you're doing that in 2 worker processes simultaneously. I bet your disk is grinding itself to dust while the OS swaps out everything it can ;-)

Change range to xrange and see what happens. I bet it will work fine then.

Upvotes: 6

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