信号量

import threading,time

def  run(n):
    semaphore.acquire()
    time.sleep(1)
    print("run in the %s thread"%n)
    semaphore.release()

if __name__ ==  '__main__':
    semaphore = threading.BoundedSemaphore(5)#最多允许5个线程同时执行
    for i in range(22):
        t = threading.Thread(target=run,args=(i,))
        t.start()

while threading.active_count() != 1:
    pass# print("active count :",threading.active_count())

else:
    print("all threads done")