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java代码则没有问题：
publicclassTest{
publicstaticvoidmain(String[]args)throwsException{
newThread(newRunnable(){
publicvoidrun(){
longstart=System.currentTimeMillis();
while(true){
try{
Thread.sleep(1000);
}catch(Exceptione){
}
System.out.println(System.currentTimeMillis());
if(System.currentTimeMillis()-start>1000*100)break;
}
}
}).start();
}
}
javaTest
ctrl-c则会结束程序
而对应的python代码：
#-*-coding:utf-8-*-
importtime
importthreading
start=time.time()
defforeverLoop():
start=time.time()
while1:
time.sleep(1)
printtime.time()
iftime.time()-start>100:
break
thread_=threading.Thread(target=foreverLoop)
#thread_.setDaemon(True)
thread_.start()
pythonp.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：
defsigint_handler(signum,frame): print"main-threadexit" 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-threadexit",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()
ift:
if__debug__:
self._note("%s:waitingforotherthreads",self)
whilet:
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-*-
importtime,signal,traceback
importsys
importthreading
start=time.time()
defforeverLoop():
start=time.time()
while1:
time.sleep(1)
printtime.time()
iftime.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:
while1:
alive=False
ifthread_.isAlive():
alive=True
ifnotalive:
break
time.sleep(1)
#为了使得统计时间能够运行，要捕捉 KeyboardInterrupt:ctrl-c
exceptKeyboardInterrupt,e:
traceback.print_exc()
print"consumetime:",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-*-
importtime,signal,traceback,os
importsys
importthreading
start=time.time()
defforeverLoop():
start=time.time()
while1:
time.sleep(1)
printtime.time()
iftime.time()-start>5:
break
classWatcher:
"""thisclasssolvestwoproblemswithmultithreaded
programsinPython,(1)asignalmightbedelivered
toanythread(whichisjustamalfeature)and(2)if
thethreadthatgetsthesignaliswaiting,thesignal
isignored(whichisabug).
Thewatcherisaconcurrentprocess(notthread)that
waitsforasignalandtheprocessthatcontainsthe
threads. SeeAppendixAofTheLittleBookofSemaphores.
http://greenteapress.com/semaphores/
IhaveonlytestedthisonLinux. Iwouldexpectitto
workontheMacintoshandnotworkonWindows.
"""
def__init__(self):
"""Createsachildthread,whichreturns. Theparent
threadwaitsforaKeyboardInterruptandthenkills
thechildthread.
"""
self.child=os.fork()
ifself.child==0:
return
else:
self.watch()
defwatch(self):
try:
os.wait()
exceptKeyboardInterrupt:
#IputthecapitalBinKeyBoardInterruptsoIcan
#tellwhentheWatchergetstheSIGINT
print'KeyBoardInterrupt'
self.kill()
sys.exit()
defkill(self):
try:
os.kill(self.child,signal.SIGKILL)
exceptOSError: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