threading.Event

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()