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() for t in threads:
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.
本文转自 https://www.cnblogs.com/fnng/p/3670789.html,如有侵权,请联系删除。