locks.py

# SuperFastPython.com
# example of a reentrant lock for processes
from time import sleep
from random import random
from multiprocessing import Process
from multiprocessing import RLock, Lock, Semaphore

# reporting function
def report(lock, identifier):
    # acquire the lock
    with lock:
        print(f'>process {identifier} done')

# work function
def task(lock, identifier, value):
    # acquire the lock
    with lock:
        print(f'>process {identifier} sleeping for {value}')
        sleep(value)
        # report
        report(lock, identifier)

# entry point
if __name__ == '__main__':
    # create a shared reentrant lock
    lock = RLock()
    # create processes
    processes = [Process(target=task, args=(lock, i, random())) for i in range(10)]
    # start child processes
    for process in processes:
        process.start()
    # wait for child processes to finish
    for process in processes:
        process.join()