信号量：　　# 相当于多个钥匙的Lock

form mutiprocessing import Semaphore

sem = Semaphore(5)

sem.acquire()

sem.release()

########################################

事件：

form mutiprocessing import Event

e = Event()

e.is_set()　　# 事件状态，默认False

e.set()　　# 状态改为Ture

e.wait()　　# 根据set值来决定是否在wait处阻塞

e.clear()　　# 状态改为False

#######################################

红绿灯

import time
import random
from multiprocessing import Process,Event

def cars(i,e):
    if not e.is_set():
        print('%s在等待...'%i)
        e.wait()
    print('%s已通过...'%i)


def traffic_light(e):
    while True:
        if e.is_set():
            e.clear()
            print('\033[31m红灯亮了\033[0m')
        else:
            e.set()
            print('\033[32m绿灯亮了\033[0m')
        time.sleep(2)


if __name__ == '__main__':
    e = Event()
    traffic = Process(target=traffic_light,args=(e,))
    traffic.start()
    for i in range(20):
        car = Process(target=cars,args=(i,e))
        car.start()
        time.sleep(random.random())