Events-事件-红绿灯

Event: 用于线程之间状态的同步。对全局变量不断地做修改。

Event=threading.Event()  #生成1个event的对象

Event.wait() #等着设定全局变量。检测标志位是否有设置，如果标志位没有设置的话，会一直卡在这里。等待标志位被设定。

如果标志位被设定了，代表绿灯，直接通行。wait不阻塞。

如果标志位被清空，代表红灯，wait等待。

多个线程可以等待同一个event的标志位的变化。

Event.set() #设置一个标志位，相当于全局变量

Event.clear() #清空标志位

Event.is_set() #判断是否设置了标志位

理解点：

1.车的线程与红绿灯的线程之间有了关联，车的线程会根据红绿灯的线程而变化。

2.每一次状态的切换，就是一次事件的发生，会相应地做不同的事情。

import time,threading

event=threading.Event()

def lighter():
    count=0
    event.set() #先设为绿灯
    while True:
        if count>5 and count<10: #改成红灯
            event.clear() #清空标志位,在红灯状态卡10s
            print('\033[41;1mred light is on..\033[0m')
        elif count>10:
            event.set()#变绿灯
            count=0
        else:
            print('\033[42;1mgreen light is on..\033[0m')
        time.sleep(1)
        count+=1

def car(name):
    while True:
        if event.is_set(): #设置了标志位，代表绿灯
            print('[%s] running...'%name)
            time.sleep(1)
        else:
            print('[%s] red light,waiting..'%name)
            event.wait()
            print('[%s] green is on, start going.'%name )

light=threading.Thread(target=lighter,)
light.start()
car1=threading.Thread(target=car,args=('Tesla',))
car1.start()

运行结果：

green light is on..
[Tesla] running...
green light is on..
[Tesla] running...
green light is on..
[Tesla] running...
[Tesla] running...
green light is on..
[Tesla] running...
green light is on..
[Tesla] running...
green light is on..
[Tesla] running...
red light is on..
red light is on..
[Tesla] red light,waiting..
red light is on..
red light is on..
green light is on..
[Tesla] green is on, start going.
[Tesla] running...
green light is on..
[Tesla] running...