Question

I am starting to learn multiprocessing in python, but have arrived to a point where my code just hangs. It is simply computing 1 000 000 factorial, using multithreading.

import multiprocessing

def part(n):
    ret = 1
    n_max = n + 9999
    while n <= n_max:
        ret *= n
        n += 1
    print "Part "+ str(n-1) + " complete"
    return ret

def buildlist(n_max):
    n = 1
    L = []
    while n <= n_max:
        L.append(n)
        n += 10000
    return L

final = 1
ne = 0
if __name__ == '__main__':
    pool = multiprocessing.Pool()
    results = [pool.apply_async(part, (x,)) for x in buildlist(1000000)]
    for r in results:
        x = r.get()
        final *= x
        ne+= 1
        print ne
    print final

I have included some print functions to try to diagnose where the code hangs, and it will print the string included in the part function 100 times, as expected. The “print ne” also works 100 times.

The problem is that final won’t print, and the code doesn’t complete.

How do I fix this problem?

Edit: Also, since this is being downvoted, could someone explain what I am doing wrong/why I am being downvoted?

Answer 1

The program works fine — until the print final. Then it spends a very large amount of time trying to print this number, which is seriously huge…