Python_事件event

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本文深入探讨了Python中线程同步机制的核心组件——事件(Event)。通过一个红绿灯控制系统的具体案例，详细解释了如何使用Event对象进行线程间的同步与通信，包括事件的设置(set)、清除(clear)和等待(wait)等关键操作。

事件（event）
An event is a simple synchronization object
the event represents an internal flag, and threads can wait for the flag
to be set, or set or clear the flags themselves

event = threading.event()

A client thread can wait for the flag to be set

event.wait()

A server thread can set or reset it

event.set()
event.clear()
If the flag is set, the wait method doesn’t do anything.
If the flag is clear, wait will block until it becomes set again.
Any number of threads may wait for the same event.
通过event来实现线程之间的交互

redlight = False

while True:
if counter > 30:
redlight = True
if counter >50:
redlight = False
counter = 0

下面以一个红绿灯的程序作为例子来理解一下事件：

# Author : Xuefeng

import threading, time

# 实例化事件
event = threading.Event()


def light():
    '''
    定义灯的函数，红灯亮5秒绿灯亮5秒。
    :return: 
    '''
    count = 0
    # 事件置位
    event.set()
    while True:
        if count > 5 and count < 10:          # Change for red light
            event.clear()       # clear the flag
            print("\033[41;1m red light is on...\033[0m")
        elif count > 10:
            event.set()         # set the flag
            count = 0
        else:
            print("\033[42;1m green light is on...\033[0m")
        time.sleep(1)
        count += 1

def car(name):
    '''
    定义汽车模型，红灯停，绿灯行
    :param name: 汽车的名字
    :return: 
    '''
    while True:
        if event.is_set():          # Green light
            print("[%s] running..." % name)
            time.sleep(1)
        else:
            print("[%s] sees red light, waitting..." %name)
            event.wait()
            print("\033[42;1m Green light on, [%s] startting...\033[0m" %name)

# 创建灯的线程
Light = threading.Thread(target=light)
Light.start()
# 创建3个小汽车
Car_1 = threading.Thread(target=car, args=("Tom",))
Car_2 = threading.Thread(target=car, args=("Jim",))
Car_3 = threading.Thread(target=car, args=("Mary",))
Car_1.start()
Car_2.start()
Car_3.start()