How to exit a main program from the Multiprocessing Process in python

For this to work you need to have communication between the worker processes and the main process. Probably the simplest way is to use multiprocessing.Event.

Before starting the processes, create a pair of multiprocessing.Event. Give them meaningful names like stop_main and stop_workers. For portability, one should give add these Events to the arguments given for the Process target.

A worker process should call stop_main.set() when it wants the main program to exit. A worker process should also call stop_workers.is_set() regularly and exit when this returns True.

After the main process starts all the workers it should keep polling stop_main.is_set(). When that returns True it should call stop_workers.set(), join the workers and exit.

Updated:

Edited to make it shorter and hopefully make it work on ms-windows.

An example:

import multiprocessing as mp
import time


def worker(num, sw, sm):
    if num == 5:
        print('This is worker', num)
        time.sleep(1)
        print('Worker', num, 'signalling main program to quit')
        sm.set()
    while not sw.is_set():
        print('This is worker', num)
        time.sleep(0.7)
    else:
        print('Worker', num, 'signing off..')


if __name__ == '__main__':
    stop_worker = mp.Event()
    stop_main = mp.Event()

    workers = [mp.Process(target=worker, args=(n, stop_worker, stop_main))
               for n in range(1, 6)]
    for w in workers:
        w.start()
    while not stop_main.is_set():
        time.sleep(1)
    print('MAIN: Received stop event')
    print('MAIN: Sending stop event to workers')
    stop_worker.set()
    for c, w in enumerate(workers, start=1):
        w.join()
        print('worker', c, 'joined')

It runs like this:

This is worker 1
This is worker 2
This is worker 3
This is worker 4
This is worker 5
This is worker 2
This is worker 3
This is worker 1
This is worker 4
Worker 5 signalling main program to quit
This is worker 5
This is worker 2
This is worker 3
This is worker 1
This is worker 4
This is worker 5
MAIN: Received stop event
MAIN: Sending stop event to workers
Worker 3 signing off..
Worker 1 signing off..
Worker 2 signing off..
worker 1 joined
worker 2 joined
worker 3 joined
Worker 4 signing off..
worker 4 joined
Worker 5 signing off..
worker 5 joined

Here's a solution. You lose all communication to the launched process once __main__ exits, but that's ok for my use-case with matplotlib. Just close the window or, as you mentioned, close the shell.

The example script is located in detail here.