Python 多线程技巧 用threading.Event代替time.sleep()
果我们碰到了这样的场景：线程1做一件时间较长的事情，等做完了，主程序去测试其状态是不是真的更改了。

通常比较容易想到的是：

1. 线程1里，用大循环来模拟这个长时间的函数，比如for i in range(1, 10000)等等；

2. 主程序里，用比如time.sleep(60)去等待，默许60秒应该已经够线程1去run了。

显然，这样做是不严谨的，因为没办法确切控制线程1的时间，所以测试程序可能会fail掉。

好的解决办法是用threading.Event的wait()和set()来精确控制线程。

见代码如下：

线程1：Work

主线程：跟踪测试is_done的状态。

#!/usr/bin/python
# -*- coding: utf-8 -*-
import threading
def DoWork(work, callback):  def Task():  print 'work begin...'  work()  print 'work done!'  print 'callback begin...'  callback()  print 'callback done!'  t = threading.Thread(target=Task)  t.start()
def TestWorkAndDone():  is_started = threading.Event()  can_done = threading.Event()  is_done = threading.Event()  def Work():  """it's not a good idea to use huge for loop here to kill time, because the start and end time are not under the control. """  print '1'  is_started.set()  print '2'  # block here until can_done.set() is called.  can_done.wait(timeout=60)  # .await() in Java  print '7'  DoWork(work=Work, callback=lambda:is_done.set())  print '3'  # block here until is_started.set() is called.  is_started.wait(timeout=60)  print '4'  if is_started.isSet():  print 'SUCCESS: Work started'  if is_done.isSet():  print 'FAILD: Work hasnot done'  print '5'  can_done.set()  # Work() is unblock.  print '6'  # block here until callback() is called.  # no need to use time.sleep(60) here.  is_done.wait(timeout=60)  if is_done.isSet():  print '<mce:script type="text/javascript" src="http://hi.images.csdn.net/js/blog/tiny_mce/themes/advanced/langs/zh.js" mce_src="http://hi.images.csdn.net/js/blog/tiny_mce/themes/advanced/langs/zh.js"></mce:script><mce:script type="text/javascript" src="http://hi.images.csdn.net/js/blog/tiny_mce/plugins/syntaxhl/langs/zh.js" mce_src="http://hi.images.csdn.net/js/blog/tiny_mce/plugins/syntaxhl/langs/zh.js"></mce:script>SUCCESS: Work done'
# main
TestWorkAndDone()