python multi-processing example using initializer function.

main.py

#!/usr/bin/env python

# This example shows how to use multiprocessing with an initializer function.
# We take advantage of that to make the workers each have a custom initial
# load. And in particular example, we will make the workers sleep.
# Because we make them sleep different amounts, one of them is going to be
# ready much before the others, and thus we can guess easily which worker
# will do most of the work.
#
# see https://stackoverflow.com/questions/26693797/python-multiprocessing-process-number
#

from multiprocessing import Pool,Queue
from time import sleep

def f(x):
    import os 
    print "process id = " , os.getpid()
    return x*x

# Queue that will hold amount of time to sleep
# for each worker in the initialization
sleeptimes = Queue()
for times in [2,3,0,2]:
    sleeptimes.put(times)

# each worker will do the following init.
# before they are handed any task.
# in our case the 3rd worker won't sleep
# and get all the work.
def slowstart(q):
    import os
    num = q.get()
    print "slowstart: process id = {0} (sleep({1}))".format(os.getpid(),num)
    sleep(num)

if __name__ == '__main__':
    pool = Pool(processes=4,initializer=slowstart,initargs=(sleeptimes,))    # start 4 worker processes
    result  =  pool.map_async(f, (11,))   #Start job 1 
    result1 =  pool.map_async(f, (10,))   #Start job 2
    print "result = ", result.get(timeout=3)
    print "result1 = ", result1.get(timeout=3)

result.txt

$ python main.py 
slowstart: process id = 97687 (sleep(2))
slowstart: process id = 97688 (sleep(3))
slowstart: process id = 97689 (sleep(0))
slowstart: process id = 97690 (sleep(2))
process id =  97689
process id =  97689
result =  [121]
result1 =  [100]