多线程和多进程是什么自行google补脑 对于python 多线程的理解,我花了很长时间,搜索的大部份文章都不够通俗易懂。所以,这里力图用简单的例子,让你对多线程有个初步的认识。
单线程
在好些年前的MS-DOS时代,操作系统处理问题都是单任务的,我想做听音乐和看电影两件事儿,那么一定要先排一下顺序。 (好吧!我们不纠结在DOS时代是否有听音乐和看影的应用。^_^) from time import ctime,sleep def music(): for i in range(2): print "I was listening to music. %s" %ctime() sleep(1) def move(): for i in range(2): print "I was at the movies! %s" %ctime() sleep(5) if __name__ == '__main__': music() move() print "all over %s" %ctime() 我们先听了一首音乐,通过for循环来控制音乐的播放了两次,每首音乐播放需要1秒钟,sleep()来控制音乐播放的时长。接着我们又看了一场电影, 每一场电影需要5秒钟,因为太好看了,所以我也通过for循环看两遍。在整个休闲娱乐活动结束后,我通过 print "all over %s" %ctime()
看了一下当前时间,差不多该睡觉了。 运行结果: >>=========================== RESTART ================================ >>> I was listening to music. Thu Apr 17 10:47:08 2014 I was listening to music. Thu Apr 17 10:47:09 2014 I was at the movies! Thu Apr 17 10:47:10 2014 I was at the movies! Thu Apr 17 10:47:15 2014 all over Thu Apr 17 10:47:20 2014
其实,music()和move()更应该被看作是音乐和视频播放器,至于要播放什么歌曲和视频应该由我们使用时决定。所以,我们对上面代码做了改造: #coding=utf-8 import threading from time import ctime,sleep def music(func): for i in range(2): print "I was listening to %s. %s" %(func,ctime()) sleep(1) def move(func): for i in range(2): print "I was at the %s! %s" %(func,ctime()) sleep(5) if __name__ == '__main__': music(u'爱情买卖') move(u'阿凡达') print "all over %s" %ctime() 对music()和move()进行了传参处理。体验中国经典歌曲和欧美大片文化。 运行结果: >>> ======================== RESTART ================================ >>> I was listening to 爱情买卖. Thu Apr 17 11:48:59 2014 I was listening to 爱情买卖. Thu Apr 17 11:49:00 2014 I was at the 阿凡达! Thu Apr 17 11:49:01 2014 I was at the 阿凡达! Thu Apr 17 11:49:06 2014 all over Thu Apr 17 11:49:11 2014
多线程
科技在发展,时代在进步,我们的CPU也越来越快,CPU抱怨,P大点事儿占了我一定的时间,其实我同时干多个活都没问题的;于是,操作系统就进入了多任务时代。我们听着音乐吃着火锅的不在是梦想。 python提供了两个模块来实现多线程thread 和threading ,thread 有一些缺点,在threading 得到了弥补,为了不浪费你和时间,所以我们直接学习threading 就可以了。 继续对上面的例子进行改造,引入threadring来同时播放音乐和视频: #coding=utf-8 import threading from time import ctime,sleep def music(func): for i in range(2): print "I was listening to %s. %s" %(func,ctime()) sleep(1) def move(func): for i in range(2): print "I was at the %s! %s" %(func,ctime()) sleep(5) threads = [] t1 = threading.Thread(target=music,args=(u'爱情买卖',)) threads.append(t1) t2 = threading.Thread(target=move,args=(u'阿凡达',)) threads.append(t2) if __name__ == '__main__': for t in threads: t.setDaemon(True) t.start() print "all over %s" %ctime()
import threading 首先导入threading 模块,这是使用多线程的前提。
threads = [] t1 = threading.Thread(target=music,args=(u'爱情买卖',)) threads.append(t1) 创建了threads数组,创建线程t1,使用threading.Thread()方法,在这个方法中调用music方法target=music,args方法对music进行传参。 把创建好的线程t1装到threads数组中。 接着以同样的方式创建线程t2,并把t2也装到threads数组。
for t in threads: t.setDaemon(True) t.start() 最后通过for循环遍历数组。(数组被装载了t1和t2两个线程)
setDaemon() setDaemon(True)将线程声明为守护线程,必须在start() 方法调用之前设置,如果不设置为守护线程程序会被无限挂起。子线程启动后,父线程也继续执行下去,当父线程执行完最后一条语句print "all over %s" %ctime()后,没有等待子线程,直接就退出了,同时子线程也一同结束。
start() 开始线程活动。
运行结果: >>> ========================= RESTART ================================ >>> I was listening to 爱情买卖. Thu Apr 17 12:51:45 2014 I was at the 阿凡达! Thu Apr 17 12:51:45 2014 all over Thu Apr 17 12:51:45 2014 从执行结果来看,子线程(muisc 、move )和主线程(print "all over %s" %ctime())都是同一时间启动,但由于主线程执行完结束,所以导致子线程也终止。
继续调整程序: ...
if __name__ == '__main__':
for t in threads:
t.setDaemon(True)
t.start()
t.join()
print "all over %s" %ctime()
我们只对上面的程序加了个join()方法,用于等待线程终止。join()的作用是,在子线程完成运行之前,这个子线程的父线程将一直被阻塞。 注意: join()方法的位置是在for循环外的,也就是说必须等待for循环里的两个进程都结束后,才去执行主进程。 运行结果: >>> ========================= RESTART ================================ >>> I was listening to 爱情买卖. Thu Apr 17 13:04:11 2014 I was at the 阿凡达! Thu Apr 17 13:04:11 2014 I was listening to 爱情买卖. Thu Apr 17 13:04:12 2014 I was at the 阿凡达! Thu Apr 17 13:04:16 2014 all over Thu Apr 17 13:04:21 2014 从执行结果可看到,music 和move 是同时启动的。 开始时间4分11秒,直到调用主进程为4分22秒,总耗时为10秒。从单线程时减少了2秒,我们可以把music的sleep()的时间调整为4秒。 ... def music(func): for i in range(2): print "I was listening to %s. %s" %(func,ctime()) sleep(4) ... 执行结果: >>> ====================== RESTART ================================ >>> I was listening to 爱情买卖. Thu Apr 17 13:11:27 2014I was at the 阿凡达! Thu Apr 17 13:11:27 2014 I was listening to 爱情买卖. Thu Apr 17 13:11:31 2014 I was at the 阿凡达! Thu Apr 17 13:11:32 2014 all over Thu Apr 17 13:11:37 2014 子线程启动11分27秒,主线程运行11分37秒。 虽然music每首歌曲从1秒延长到了4 ,但通多程线的方式运行脚本,总的时间没变化。
本文从感性上让你快速理解python多线程的使用,更详细的使用请参考其它文档或资料。 ========================================================== class threading.Thread()说明:
class threading.Thread(group=None, target=None, name=None, args=(), kwargs={}) This constructor should always be called with keyword arguments. Arguments are: group should be None; reserved for future extension when a ThreadGroup class is implemented. target is the callable object to be invoked by the run() method. Defaults to None, meaning nothing is called. name is the thread name. By default, a unique name is constructed of the form “Thread-N” where N is a small decimal number. args is the argument tuple for the target invocation. Defaults to (). kwargs is a dictionary of keyword arguments for the target invocation. Defaults to {}. If the subclass overrides the constructor, it must make sure to invoke the base class constructor (Thread.__init__()) before doing anything else to the thread.
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