lesson04_semaphore.py

# SuperFastPython.com
# example of a semaphore to limit access to resource
from time import sleep
from random import random
from threading import Thread
from threading import Semaphore

# custom function to be executed in a new thread
def task(shared_semaphore, ident):
 # attempt to acquire the semaphore
 with shared_semaphore:
 # generate a random value between 0 and 1
 val = random()
 # block for a fraction of a second
 sleep(val)
 # report result
 print(f'Thread {ident} got {val}')

# protect the entry point
if __name__ == '__main__':
 # create the shared semaphore
 semaphore = Semaphore(2)
 # create threads
 threads = [Thread(target=task,
 args=(semaphore, i)) for i in range(10)]
 # start new threads
 for thread in threads:
 thread.start()
 # wait for new threads to finish
 for thread in threads:
 thread.join()