Imap_unordered

The imap_unordered is aptly named as such, because when used, it returns an iterable map, and it executes the tasks submitted to it in an unordered fashion:

from multiprocessing import Pool
import time

def myTask(n):
 time.sleep(n+2)
 return n+2

def main():
 with Pool(4) as p:
   for iter in p.imap_unordered(myTask, [1,3,2,1]):
     print(iter)
 
if __name__ == '__main__':
 main()

Upon execution of this preceding program, you should see something like this:

$ python3.6 17_mapPool.py
3
3
4
5

We've been returned an iterable that contains transformed elements, which are not in the same order as they were inputted. imap_unordered has returned the elements in the order in which they completed.