python 多线程， so easy

python3.jpg

好久没有看多线程了把基础都快忘了，今天突然想复习一下.

在很久很久以前，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。

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。

之后我们对上述函数进行了改进。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()

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'沉默是金',))
threads.append(t1)
t2 = threading.Thread(target=move,args=(u'时空穿越',))
threads.append(t2)

if __name__ == '__main__':
    for t in threads:
        t.setDaemon(True)
        t.start()
    print ("all over %s" %ctime())

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。输出结果如下

C:\Python34\python.exe C:/Users/ecaoyng/PycharmProjects/py3Demo/multi_thread.py
I was listening to 沉默是金. Thu Sep  7 10:08:58 2017
I was at the 时空穿越! Thu Sep  7 10:08:58 2017
all over Thu Sep  7 10:08:58 2017

Process finished with exit code 0

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。
继续调整主程序

if __name__ == '__main__':
    for t in threads:
        t.setDaemon(True)
        t.start()

    t.join()
    print("all over %s" % ctime())

执行结果如下：

C:\Python34\python.exe C:/Users/ecaoyng/PycharmProjects/py3Demo/multi_thread.py
I was listening to 沉默是金. Thu Sep  7 10:12:30 2017
I was watching at the 时空穿越! Thu Sep  7 10:12:30 2017
I was listening to 沉默是金. Thu Sep  7 10:12:31 2017
I was watching at the 时空穿越! Thu Sep  7 10:12:35 2017
all over Thu Sep  7 10:12:40 2017

Process finished with exit code 0

Process finished with exit code 0

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。

==========================================================

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.