python multiprocessing lock example

lock_demo.py

import multiprocessing
import multiprocessing.synchronize
import random
import time


def print_func(process_index: int) -> None:
    for x in "hello world":
        print(x, end='',  flush=True)

        # sleep a random amount of seconds to scramble the order of printed characters.
        time.sleep(random.random() / 10)
    print(' ', process_index,  flush=True)


def demo_func_no_lock(process_index: int) -> None:
    print_func(process_index)


def demo_func_with_lock(lock: multiprocessing.synchronize.Lock, process_index: int) -> None:
    lock.acquire()
    print_func(process_index)
    lock.release()


if __name__ == "__main__":
    lock = multiprocessing.Lock()

    procs = []
    for index in range(4):

        # TODO: uncomment one of the two lines below to see the difference in print output.
        # proc = multiprocessing.Process(target=demo_func_no_lock, args=(index,))
        # proc = multiprocessing.Process(target=demo_func_with_lock, args=(lock, index))

        procs.append(proc)
        proc.start()

    for proc in procs:
        proc.join()