from threading import Thread,Semaphore,currentThread
import time

#定义信号量(3把锁)
sm = Semaphore(3)

def task():
   
    with sm:
        print('%s acquires the sm' % currentThread().getName())
        time.sleep(1)

if __name__ == '__main__':
    for i in range(10):
        t = Thread(target=task)
        t.start()

sm.acquire()
print('%s acquires the sm'%currentThread().getName())
sm.release()

#等价于
with sm:
    print('%s acquires the sm'%currentThread().getName())