python中多线程编程_Python的多线程编程-优快云博客

提到多线程，很多人就会望而却步，本文将由浅入深地带你攻克python多线程编程，并防止你跳入深坑，

首先看一段简单的代码：

1 from time importctime,sleep2 defplay_video(video):3 for i in range(2):4 print "i am playing video: %s at %s"%(video,ctime())5 sleep(4)6

8 defplay_music(music):9 for i in range(2):10 print "i am playing music: %s at %s"%(music,ctime())11 sleep(2)12

14 if __name__=="__main__":15

16 play_video("speed_and_crazy")17 play_music("chengdu")18

19 print "all are over at %s"%ctime()20

执行结果：

C:\Python27>python mui_thread.py

i am playing video: speed_and_crazy at Mon Jun26 23:01:59 2017i am playing video: speed_and_crazy at Mon Jun26 23:02:03 2017i am playing music: chengdu at Mon Jun26 23:02:07 2017i am playing music: chengdu at Mon Jun26 23:02:09 2017all are over at Mon Jun26 23:02:11 2017

随着人们对多任务的要求，同时为了充分利用cpu资源，多线程编程不可避免，那么我们如何利用python去实现play_video和play_music

两个任务同时运行呢？

1 from time importctime,sleep2 importthreading3 defplay_video(video):4 for i in range(2):5 print "i am playing video: %s at %s \n"%(video,ctime())6 sleep(5)7

9 defplay_music(music):10 for i in range(2):11 print "i am playing music: %s at %s \n"%(music,ctime())12 sleep(1)13

14 threads=[]15

16 thread1=threading.Thread(target=play_video,args=("speed_and_crazy",))17

18 threads.append(thread1)19

20 thread2=threading.Thread(target=play_music,args=("chengdu",))21

22 threads.append(thread2)23

26 if __name__=="__main__":27

28 for thread inthreads:29 thread.setDaemon(True) #将线程声明为守护线程，必须在start()方法调用之前，如果不设置为守护线程,程序会被无限挂起30 thread.start()31

32 print "all are over at %s \n"%ctime()33

测试结果：

C:\Python27>python mui_thread.py

i am playing video: speed_and_crazy at Mon Jun26 23:18:52 2017all are over at Mon Jun26 23:18:52 2017i am playing music: chengdu at Mon Jun26 23:18:52 2017 #从打印的时间可知，play_video、play_music和父进程几乎同时运行

从结果看，与我们最初的目标相差甚远，怎么没有按照顺序执行，为什么每个函数都只有一条日记输出？

那是因为子线程(play_video、play_music)和主线程print "all are over at %s \n"%ctime()都是同一时间启动，但由于主线程已经运行结束，所以导致子线程也同时终止，在这种条件下，我们如何保证子进程都能够执行完毕呢？

增加thread.join()并放在循环外

from time importctime,sleepimportthreadingdefplay_video(video):for i in range(2):print "i am playing video: %s at %s \n"%(video,ctime())

sleep(1)defplay_music(music):for i in range(2):print "i am playing music: %s at %s \n"%(music,ctime())

sleep(5)

threads=[]

thread1=threading.Thread(target=play_video,args=("speed_and_crazy",))

threads.append(thread1)

thread2=threading.Thread(target=play_music,args=("chengdu",))

threads.append(thread2)if __name__=="__main__":for thread inthreads:

thread.setDaemon(True)

thread.start()

thread.join() #加在循环外，print "all are over at %s \n"%ctime()

运行结果：

1 C:\Python27>python mui_thread.py2 i am playing video: speed_and_crazy at Mon Jun 26 23:32:21 2017

3 i am playing music: chengdu at Mon Jun 26 23:32:21 2017

6 i am playing video: speed_and_crazy at Mon Jun 26 23:32:22 2017

8 i am playing music: chengdu at Mon Jun 26 23:32:26 2017

10 all are over at Mon Jun 26 23:32:31 2017

thread.join()的作用是主线程必须等待子线程都执行完了才能结束，play_video、play_music几乎同时执行

但是如果改变play_video、play_music里面的sleep的时长，即是下面的代码：

from time importctime,sleepimportthreadingdefplay_video(video):for i in range(2):print "i am playing video: %s at %s \n"%(video,ctime())

sleep(5)defplay_music(music):for i in range(2):print "i am playing music: %s at %s \n"%(music,ctime())

sleep(1)

threads=[]

thread1=threading.Thread(target=play_video,args=("speed_and_crazy",))

threads.append(thread1)

thread2=threading.Thread(target=play_music,args=("chengdu",))

threads.append(thread2)if __name__=="__main__":for thread inthreads:

thread.setDaemon(True)

thread.start()

thread.join()print "all are over at %s \n"%ctime()

此时运行结果：

C:\Python27>python mui_thread.py

i am playing video: speed_and_crazy at Mon Jun26 23:44:13 2017i am playing music: chengdu at Mon Jun26 23:44:13 2017i am playing music: chengdu at Mon Jun26 23:44:14 2017all are over at Mon Jun26 23:44:15 2017

我们看到play_video还有一条log没有打印出来，原因是thread.join()在循环外，此时的thread为play_music，父进程只会等待play_music进程执行完就结束，而不会等待play_video(sleep时间较长)执行完才结束，所以才会有上面的结果