python 多线程 start_new_thread()

一、简述

　　CPython实现细节： 由于GIL（Global Interpreter Lock），在CPython中一次只能有一个线程来执行python代码，不过有些面向执行的库可以克服这个限制。如果想要使你的应用程序更好的利用计算机资源的话，最好使用multiprocessing。 但是，如果同时运行多个I/O任务的话，线程依然是一个很好地选择。
　　python线程的作用主要是应对I/O任务，例如网络数据的读写等。

二、示例

　　1. 函数说明。
　　start_new_thread ( function , args [ , kwargs ] )
　　创建一个新的线程，返回一个线程标识符。function是线程函数，args是线程函数的参数，是一个list。kwargs可选参数，可不填。

#!/usr/bin/env python

# _*_ coding = utf-8 _*_

import thread
import time

def work_thread(id):

    cnt = 1

    print "Thread %d is runing..." % id

    while True:
        print "Thread with ID %d has counter value %d" % (id, cnt)
        time.sleep(2) 
        cnt += 1


for i in range(1,5):
    thread.start_new_thread(work_thread,(i,))

print "Main thread doing an infinite wait loop..."

while True:
    pass

运行代码，输出结果如下：

$ ./thread_demo.py
Main thread doing an infinite wait loop…
Thread 3 is runing…
Thread 1 is runing…
Thread 2 is runing…
Thread 4 is runing…
Thread with ID 1 has counter value 1
Thread with ID 4 has counter value 1
Thread with ID 2 has counter value 1
Thread with ID 3 has counter value 1
Thread with ID 2 has counter value 2
Thread with ID 3 has counter value 2
Thread with ID 4 has counter value 2
Thread with ID 1 has counter value 2
Thread with ID 3 has counter value 3
Thread with ID 4 has counter value 3
Thread with ID 1 has counter value 3
Thread with ID 2 has counter value 3
Thread with ID 1 has counter value 4
Thread with ID 4 has counter value 4
Thread with ID 2 has counter value 4
Thread with ID 3 has counter value 4

线程退出函数：
thread.exit ()。结束当前线程。调用该函数会触发 SystemExit 异常，如果没有处理该异常，线程将结束。