from __future__ import print_function

import multiprocessing
import time

"""
Date: 26/01/2013

Bug explication
---------------
Why when we import a module with .c compiled module,
multiprocessing (pool.imap and map) don't use all cores.

This bug exists on latest Ubuntu 64bits (both kernels 3.5 and 3.8rc4). It does
not exist for Windows Seven 32 bits (Virtualbox). Not tested on Mac OS X.

Python 2.7.3
"""


def compute(args):
    """
    Dummy computations
    """
    M = 350
    ss = [0] * M
    for a in xrange(1, M):
        a2 = a * a
        for b in xrange(1, M - a):
            s = a2 + b * b
            for c in xrange(1, M - a - b):
                if s == c * c:
                    ss[a + b + c] += 1
    return args[0]


def main():
    pool = multiprocessing.Pool(processes=5)
    pool.imap_unordered(compute, range(20))

    pool.close()
    pool.join()

if __name__ == '__main__':
    t = time.time()
    main()
    print("* Time using all cores: %f" % (time.time() - t))

    # Here we import numpy but it works with module with .c compiled module
    # Same behaviour as numpy for: skimage, scipy, tables and pandas
    print ("* Import a module containing .c compiled module (here we use numpy)")
    import numpy

    t = time.time()
    main()
    print("* Time using only one core (check it with 'htop' command on Linux system: %f" % (time.time() - t))