探寻python多线程ctrl+c退出问题解决方案
探寻python多线程ctrl+c退出问题解决方案
发布时间:2016-12-28 来源:查字典编辑
摘要:场景:经常会遇到下述问题:很多iobusy的应用采取多线程的方式来解决,但这时候会发现python命令行不响应ctrl-c了,而对应的jav...

场景:

经常会遇到下述问题:很多io busy的应用采取多线程的方式来解决,但这时候会发现python命令行不响应ctrl-c 了,而对应的java代码则没有问题:

复制代码 代码如下:

public class Test {

public static void main(String[] args) throws Exception {

new Thread(new Runnable() {

public void run() {

long start = System.currentTimeMillis();

while (true) {

try {

Thread.sleep(1000);

} catch (Exception e) {

}

System.out.println(System.currentTimeMillis());

if (System.currentTimeMillis() - start > 1000 * 100) break;

}

}

}).start();

}

}

java Test

ctrl-c则会结束程序

而对应的python代码:

复制代码 代码如下:

# -*- coding: utf-8 -*-

import time

import threading

start=time.time()

def foreverLoop():

start=time.time()

while 1:

time.sleep(1)

print time.time()

if time.time()-start>100:

break

thread_=threading.Thread(target=foreverLoop)

#thread_.setDaemon(True)

thread_.start()

python p.py

后ctrl-c则完全不起作用了。

不成熟的分析:

首先单单设置 daemon 为 true 肯定不行,就不解释了。当daemon为 false 时,导入python线程库后实际上,threading会在主线程执行完毕后,检查是否有不是 daemon 的线程,有的化就wait,等待线程结束了,在主线程等待期间,所有发送到主线程的信号也会被阻测,可以在上述代码加入signal模块验证一下:

复制代码 代码如下:

def sigint_handler(signum,frame):

print "main-thread exit"

sys.exit()

signal.signal(signal.SIGINT,sigint_handler)

在100秒内按下ctrl-c没有反应,只有当子线程结束后才会出现打印 "main-thread exit",可见 ctrl-c被阻测了

threading 中在主线程结束时进行的操作:

复制代码 代码如下:

_shutdown = _MainThread()._exitfunc

def _exitfunc(self):

self._Thread__stop()

t = _pickSomeNonDaemonThread()

if t:

if __debug__:

self._note("%s: waiting for other threads", self)

while t:

t.join()

t = _pickSomeNonDaemonThread()

if __debug__:

self._note("%s: exiting", self)

self._Thread__delete()

对所有的非daemon线程进行join等待,其中join中可自行察看源码,又调用了wait,同上文分析 ,主线程等待到了一把锁上。

不成熟的解决:

只能把线程设成daemon才能让主线程不等待,能够接受ctrl-c信号,但是又不能让子线程立即结束,那么只能采用传统的轮询方法了,采用sleep间歇省点cpu吧:

复制代码 代码如下:

# -*- coding: utf-8 -*-

import time,signal,traceback

import sys

import threading

start=time.time()

def foreverLoop():

start=time.time()

while 1:

time.sleep(1)

print time.time()

if time.time()-start>5:

break

thread_=threading.Thread(target=foreverLoop)

thread_.setDaemon(True)

thread_.start()

#主线程wait住了,不能接受信号了

#thread_.join()

def _exitCheckfunc():

print "ok"

try:

while 1:

alive=False

if thread_.isAlive():

alive=True

if not alive:

break

time.sleep(1)

#为了使得统计时间能够运行,要捕捉 KeyboardInterrupt :ctrl-c

except KeyboardInterrupt, e:

traceback.print_exc()

print "consume time :",time.time()-start

threading._shutdown=_exitCheckfunc

缺点:轮询总会浪费点cpu资源,以及battery.

有更好的解决方案敬请提出。

ps1: 进程监控解决方案 :

用另外一个进程来接受信号后杀掉执行任务进程,牛

复制代码 代码如下:

# -*- coding: utf-8 -*-

import time,signal,traceback,os

import sys

import threading

start=time.time()

def foreverLoop():

start=time.time()

while 1:

time.sleep(1)

print time.time()

if time.time()-start>5:

break

class Watcher:

"""this class solves two problems with multithreaded

programs in Python, (1) a signal might be delivered

to any thread (which is just a malfeature) and (2) if

the thread that gets the signal is waiting, the signal

is ignored (which is a bug).

The watcher is a concurrent process (not thread) that

waits for a signal and the process that contains the

threads. See Appendix A of The Little Book of Semaphores.

http://greenteapress.com/semaphores/

I have only tested this on Linux. I would expect it to

work on the Macintosh and not work on Windows.

"""

def __init__(self):

""" Creates a child thread, which returns. The parent

thread waits for a KeyboardInterrupt and then kills

the child thread.

"""

self.child = os.fork()

if self.child == 0:

return

else:

self.watch()

def watch(self):

try:

os.wait()

except KeyboardInterrupt:

# I put the capital B in KeyBoardInterrupt so I can

# tell when the Watcher gets the SIGINT

print 'KeyBoardInterrupt'

self.kill()

sys.exit()

def kill(self):

try:

os.kill(self.child, signal.SIGKILL)

except OSError: pass

Watcher()

thread_=threading.Thread(target=foreverLoop)

thread_.start()

注意 watch()一定要放在线程创建前,原因未知。。。。,否则立刻就结束

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