python - threading-信号量示例

import threading
import time

def run (n):
    semaphore.acquire()
    time.sleep(1)
    print("run threading :",n)
    semaphore.release()
semaphore=threading.BoundedSemaphore(4)
for  i in range(20):
    t=threading.Thread(target=run,args=(i,))
    t.start()
while(threading.activeCount != 1):
    pass
else:
    print("main threading done.....")