test_multiprocess.py

import multiprocessing

POISON_PILL = "STOP"

def process_odds(in_queue, shared_list):

    while True:

        # block until something is placed on the queue
        new_value = in_queue.get()

        # check to see if we just got the poison pill
        if new_value == POISON_PILL:
            break

        # we didn't, so do the processing and put the result in the
        # shared data structure
        shared_list.append(new_value)

    return

def process_evens(in_queue, shared_list):

    while True:
        new_value = in_queue.get()
        if new_value == POISON_PILL:
            break

        shared_list.append(new_value/-2)

    return

def main():

    # create a manager - it lets us share native Python object types like
    # lists and dictionaries without worrying about synchronization -
    # the manager will take care of it
    manager = multiprocessing.Manager()

    # now using the manager, create our shared data structures
    odd_queue = manager.Queue()
    #even_queue = manager.Queue()
    shared_list = manager.list()

    # lastly, create our pool of workers - this spawns the processes,
    # but they don't start actually doing anything yet
    pool = multiprocessing.Pool()

    # now we'll assign two functions to the pool for them to run -
    # one to handle even numbers, one to handle odd numbers
    odd_result = pool.apply_async(process_odds, (odd_queue, shared_list))
    #even_result = pool.apply_async(process_evens, (even_queue, shared_list))
    # this code doesn't do anything with the odd_result and even_result
    # variables, but you have the flexibility to check exit codes
    # and other such things if you want - see docs for AsyncResult objects

    # now that the processes are running and waiting for their queues
    # to have something, lets give them some work to do by iterating
    # over our data, deciding who should process it, and putting it in
    # their queue
    for i in range(1000000):

        #if (i % 2) == 0: # use mod operator to see if "i" is even
        #    even_queue.put(i)

        #else:
            odd_queue.put(i)

    # now we've finished giving the processes their work, so send the
    # poison pill to tell them to exit
    #even_queue.put(POISON_PILL)
    odd_queue.put(POISON_PILL)

    # wait for them to exit
    pool.close()
    pool.join()

    # now we can check the results
    print(len(shared_list))

    # ...and exit!
    return


if __name__ == "__main__":
    main()