红绿灯

import time
import random
from multiprocessing import Process,Event

def cars(e,i):
    if not e.is_set():
        print('car%d在等待'%i)
        e.wait()
    print('\033[33mcar%i通过\033[0m' % i)


def 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()
    p = Process(target=light,args=(e,))
    p.start()
    for i in range(1,21):
        p = Process(target=cars,args=(e,i))
        p.start()
        time.sleep(random.random())