python3 Semaphore

同进程的一样

Semaphore管理一个内置的计数器，

每当调用acquire()时内置计数器-1；

调用release() 时内置计数器+1；

计数器不能小于0；当计数器为0时，acquire()将阻塞线程直到其他线程调用release()。

 

实例：(同时只有5个线程可以获得semaphore,即可以限制最大连接数为5)：

from threading import Thread,Semaphore
import threading
import time
 
def task():
    sm.acquire()
    print(f"{threading.current_thread().name} get sm")
    time.sleep(3)
    sm.release()
 
 
if __name__ == '__main__':
    sm = Semaphore(5) # 同一时间只有5个线程可以执行。
    for i in range(20):
        t = Thread(target=task)
        t.start()

outputs 

macname@MacdeMacBook-Pro py % python3 cccccc.py
Thread-1 get sm
Thread-2 get sm
Thread-4 get sm
Thread-5 get sm
Thread-3 get sm
Thread-6 get sm
Thread-7 get sm
Thread-9 get sm
Thread-10 get sm
Thread-8 get sm
Thread-11 get sm
Thread-13 get sm
Thread-12 get sm
Thread-14 get sm
Thread-15 get sm
Thread-16 get sm
Thread-17 get sm
Thread-19 get sm
Thread-20 get sm
Thread-18 get sm
macname@MacdeMacBook-Pro py %