python threading中的join和setDaemon方法

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python 多线程的threading中的join和setDaemon方法

join():通俗的将就是阻止子线程随着主线程的结束而结束

setDaemon()：设置子线程是否随着主线程的结束而结束，其中：

setDaemon(True) : 设置子线程随着主线程的结束而结束

setDaemon(False) 等价于join() :设置子线程不随着主线程的结束而结束

修改http://blog.youkuaiyun.com/sjyu_ustc/article/details/71080834代码如下：

#!/usr/bin/python
# -*- coding: utf-8 -*-

import threading,time

def test(loop, sec):
    print 'start loop', loop, 'at:', time.ctime()
    time.sleep(sec)
    print 'loop', loop, 'done at:', time.ctime()

def main():
    print 'starting at:', time.ctime()
    thpool = []
    for i in xrange(10):
        th = threading.Thread(target= test,args= (i,2))
        th.start()
        thpool.append(th)
    for th in thpool:
        th.join()
    print 'all Done at:', time.ctime()

if __name__ == '__main__':
        main()

结果：

starting at: Tue May  2 14:31:41 2017
start loop 0 at: Tue May  2 14:31:41 2017
start loop 1 at: Tue May  2 14:31:41 2017
start loop 2 at: Tue May  2 14:31:41 2017
start loop 3 at: Tue May  2 14:31:41 2017
start loop 4 at: Tue May  2 14:31:41 2017
start loop 5 at: Tue May  2 14:31:41 2017
start loop 6 at: Tue May  2 14:31:41 2017
start loop 7 at: Tue May  2 14:31:41 2017
start loop 8 at: Tue May  2 14:31:41 2017
start loop 9 at: Tue May  2 14:31:41 2017
loop 0 done at: Tue May  2 14:31:43 2017
loop 1 done at: looploop  4 loopdone at:  Tue May  2 14:31:43 2017
2Tue May  2 14:31:43 2017
 done at: Tue May  2 14:31:43 2017
3 done at: Tue May  2 14:31:43 2017
loop 5 done at: Tue May  2 14:31:43 2017
loop 6 done at: Tue May  2 14:31:43 2017
loop 7 done at: Tue May  2 14:31:43 2017
loop 8 done at: Tue May  2 14:31:43 2017
loop 9 done at: Tue May  2 14:31:43 2017
all Done at: Tue May  2 14:31:43 2017

可以看出修改前join方法使得每个子线程顺序执行，所有子线程执行完毕后，主线程才退出。修改后，所有子线程几乎同时执行，之后主线程执行在退出。

修改为setDaemon方法，继续观察：

#!/usr/bin/python
# -*- coding: utf-8 -*-

import threading,time

def test(loop, sec):
    print 'start loop', loop, 'at:', time.ctime()
    time.sleep(sec)
    print 'loop', loop, 'done at:', time.ctime()

def main():
    print 'starting at:', time.ctime()
    for i in xrange(10):
        th = threading.Thread(target= test,args= (i,2))
        th.setDaemon(True)
        th.start()
        
    print 'all Done at:', time.ctime()

if __name__ == '__main__':
        main()

结果：

starting at: Tue May  2 14:57:48 2017
start loop 0 at: Tue May  2 14:57:48 2017
start loop 1 at: Tue May  2 14:57:48 2017
start loop 2 at: Tue May  2 14:57:48 2017
start loop 3 at: Tue May  2 14:57:48 2017
start loop 4 at: Tue May  2 14:57:48 2017
start loop 5 at: Tue May  2 14:57:48 2017
start loop 6 at: Tue May  2 14:57:48 2017
start loop 7 at: Tue May  2 14:57:48 2017
start loop 8 at: Tue May  2 14:57:48 2017
start loop 9 at:all Done at: Tue May  2 14:57:48 2017
 Tue May  2 14:57:48 2017

可以看出子线程都还没执行完，因为主线程退出也都随着主线程退出了

#!/usr/bin/python
# -*- coding: utf-8 -*-

import threading,time

def test(loop, sec):
    print 'start loop', loop, 'at:', time.ctime()
    time.sleep(sec)
    print 'loop', loop, 'done at:', time.ctime()

def main():
    print 'starting at:', time.ctime()
    for i in xrange(10):
        th = threading.Thread(target= test,args= (i,2))
        th.setDaemon(False)
        th.start()
        
    print 'all Done at:', time.ctime()

if __name__ == '__main__':
        main()

结果：

starting at: Tue May  2 15:01:46 2017
start loop 0 at: Tue May  2 15:01:46 2017
start loop 1 at: Tue May  2 15:01:46 2017
start loop 2 at: Tue May  2 15:01:46 2017
start loop 3 at: Tue May  2 15:01:46 2017
start loop 4 at: Tue May  2 15:01:46 2017
 start loop 5 at: Tue May  2 15:01:46 2017
start loop 6 at: Tue May  2 15:01:46 2017
start loop 7 at: Tue May  2 15:01:46 2017
start loop 8 at: Tue May  2 15:01:46 2017
start loop 9 all Done at: Tue May  2 15:01:46 2017
at: Tue May  2 15:01:46 2017
loop 0 done at: Tue May  2 15:01:48 2017
loop 5 done at: Tue May  2 15:01:48 2017
 loop 3 done at:loop 2 done at: Tue May  2 15:01:48 2017
 Tue May  2 15:01:48 2017
 loop 1 done at: Tue May  2 15:01:48 2017
loop 4 done at: Tue May  2 15:01:48 2017
loop 6 done at: Tue May  2 15:01:48 2017
loop 7 done at: Tue May  2 15:01:48 2017
loop 8 done at: Tue May  2 15:01:48 2017
loop 9 done at: Tue May  2 15:01:48 2017

设置为false后，主线程退出后，子线程并没随着主线程的退出而退出