pythonの信号量

#!/usr/bin/env python
import threading,time

def run(n):
    # 申请锁
    semaphore.acquire()
    time.sleep(1)
    print("run thre thread:%s\n"%n)
    # 释放锁
    semaphore.release()

if __name__ == "__main__":
    # 申请线程池，每次最多开辟五个线程
    semaphore = threading.BoundedSemaphore(5)

    for i in range(22):
        # 开启一个线程
        t = threading.Thread(target=run,args=(i,))
        t.start()
while threading.active_count() !=1:
    pass

else :
    print("all threads done")