Question

I have python2.5 and multiprocessoring (get from http://code.google.com/p/python-multiprocessing/)

This simple code (get from docs), works very strange from time to time, sometimes it ok, but sometimes it throw timeout ex or hang my Windows (Vista), only reset helps 🙂 Why this can happen?

from multiprocessing import Pool

def f(x):
    print "fc",x
    return x*x
pool = Pool(processes=4)  
if __name__ == '__main__':
    result = pool.apply_async(f, (10,))     # evaluate "f(10)" asynchronously
    print result.get(timeout=3)           # prints "100" unless your computer is *very* slow

Answer 1

This is just a wild guess, but have you tried to move the Pool creation into the if block? I suspect that otherwise it might spawn an unlimited number of new processes, causing the freeze.