threading Event

通过threading.Event()可以创建一个事件管理标志，该标志（event）默认为False，event对象主要有四种方法可以调用：

 event.wait(timeout=None)：调用该方法的线程会被阻塞，如果设置了timeout参数，超时后，线程会停止阻塞继续执行；
 event.set()：将event的标志设置为True，调用wait方法的所有线程将被唤醒；
 event.clear()：将event的标志设置为False，调用wait方法的所有线程将被阻塞；

event.isSet()：判断event的标志是否为True。

实例代码，

两个线程  countdown，countup, countdown里面触发某个条件时(遍历的值大于5时) 再触发 执行 countup线程。

from threading import Thread, Event
import time

# Code to execute in an independent thread
def countdown(n, started_evt):
    print('countdown starting')
    for i in range(n):
        print("num is %d" % i)
        if i > 5:
            started_evt.set()
        time.sleep(1)

def countup(started_evt):
    print("countup is waiting")
    started_evt.wait()
    print('countup starting')

# Create the event object that will be used to signal startup
started_evt = Event()

# Launch the thread and pass the startup event
print('process start')
t1 = Thread(target=countdown, args=(10,started_evt))
t2 = Thread(target=countup, args=(started_evt,))
t1.start()
t2.start()

print('process is running')

执行结果：

[root@localhost comtest]# python3 test2.py
process start
countdown starting
num is 0
countup is waiting
process is running
num is 1
num is 2
num is 3
num is 4
num is 5
num is 6
countup starting
num is 7
num is 8
num is 9