欧美bbbwbbbw肥妇,免费乱码人妻系列日韩,一级黄片

探尋python多線程ctrl+c退出問題解決方案

 更新時間:2014年10月23日 11:40:21   投稿:hebedich  
這篇文章主要講述了探尋python多線程ctrl-c退出問題解決方案,需要的朋友可以參考下

場景:

經(jīng)常會遇到下述問題:很多io busy的應(yīng)用采取多線程的方式來解決,但這時候會發(fā)現(xiàn)python命令行不響應(yīng)ctrl-c 了,而對應(yīng)的java代碼則沒有問題:

復(fù)制代碼 代碼如下:

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則會結(jié)束程序

而對應(yīng)的python代碼:

復(fù)制代碼 代碼如下:

# -*- 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則完全不起作用了。

不成熟的分析:

首先單單設(shè)置 daemon 為 true 肯定不行,就不解釋了。當(dāng)daemon為 false 時,導(dǎo)入python線程庫后實際上,threading會在主線程執(zhí)行完畢后,檢查是否有不是 daemon 的線程,有的化就wait,等待線程結(jié)束了,在主線程等待期間,所有發(fā)送到主線程的信號也會被阻測,可以在上述代碼加入signal模塊驗證一下:

復(fù)制代碼 代碼如下:

def sigint_handler(signum,frame):   
    print "main-thread exit" 
    sys.exit()   
signal.signal(signal.SIGINT,sigint_handler) 

在100秒內(nèi)按下ctrl-c沒有反應(yīng),只有當(dāng)子線程結(jié)束后才會出現(xiàn)打印 "main-thread exit",可見 ctrl-c被阻測了

threading 中在主線程結(jié)束時進行的操作:

復(fù)制代碼 代碼如下:

_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() 
 

 對所有的非daemon線程進行join等待,其中join中可自行察看源碼,又調(diào)用了wait,同上文分析 ,主線程等待到了一把鎖上。

不成熟的解決:

只能把線程設(shè)成daemon才能讓主線程不等待,能夠接受ctrl-c信號,但是又不能讓子線程立即結(jié)束,那么只能采用傳統(tǒng)的輪詢方法了,采用sleep間歇省點cpu吧:
 

復(fù)制代碼 代碼如下:

# -*- 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() 
 
#主線程wait住了,不能接受信號了 
#thread_.join() 
 
def _exitCheckfunc(): 
    print "ok" 
    try: 
        while 1: 
            alive=False 
            if thread_.isAlive(): 
                alive=True 
            if not alive: 
                break 
            time.sleep(1)   
    #為了使得統(tǒng)計時間能夠運行,要捕捉  KeyboardInterrupt :ctrl-c       
    except KeyboardInterrupt, e: 
        traceback.print_exc() 
    print "consume time :",time.time()-start 
         
threading._shutdown=_exitCheckfunc 

   缺點:輪詢總會浪費點cpu資源,以及battery.

有更好的解決方案敬請?zhí)岢觥?/p>

ps1: 進程監(jiān)控解決方案 :

用另外一個進程來接受信號后殺掉執(zhí)行任務(wù)進程,牛

復(fù)制代碼 代碼如下:

# -*- 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()一定要放在線程創(chuàng)建前,原因未知。。。。,否則立刻就結(jié)束

相關(guān)文章

最新評論