探寻python多线程ctrl+c退出问题解决方案

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：

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：

# -*- 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：

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：

_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：
 

# -*- 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

# -*- 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