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Python線程創(chuàng)建和終止實(shí)例代碼

更新時(shí)間：2018年01月20日 13:54:05 作者：claireyuancy

這篇文章主要介紹了Python線程創(chuàng)建和終止實(shí)例代碼，小編覺得還是挺不錯(cuò)的，具有一定借鑒價(jià)值，需要的朋友可以參考下

python主要是通過thread和threading這兩個(gè)模塊來實(shí)現(xiàn)多線程支持。

python的thread模塊是比較底層的模塊，python的threading模塊是對thread做了一些封裝，能夠更加方便的被使用?？墒莗ython（cpython）因?yàn)镚IL的存在無法使用threading充分利用CPU資源，假設(shè)想充分發(fā)揮多核CPU的計(jì)算能力須要使用multiprocessing模塊(Windows下使用會有諸多問題)。

假設(shè)在對線程應(yīng)用有較高的要求時(shí)能夠考慮使用Stackless Python來完畢。Stackless Python是Python的一個(gè)改動(dòng)版本號，對多線程編程有更好的支持，提供了對微線程的支持。微線程是輕量級的線程，在多個(gè)線程間切換所需的時(shí)間很多其它，占用資源也更少。

通過threading模塊創(chuàng)建新的線程有兩種方法：一種是通過threading.Thread(Target=executable Method)-即傳遞給Thread對象一個(gè)可運(yùn)行方法（或?qū)ο螅?另外一種是繼承threading.Thread定義子類并重寫run()方法。另外一種方法中，唯一必須重寫的方法是run()，可依據(jù)需要決定是否重寫__init__()。值得注意的是，若要重寫__init__()，父類的__init__()必需要在函數(shù)第一行調(diào)用，否則會觸發(fā)錯(cuò)誤“AssertionError: Thread.__init__() not called”

Python threading模塊不同于其它語言之處在于它沒有提供線程的終止方法，通過Python threading.Thread()啟動(dòng)的線程彼此是獨(dú)立的。若在線程A中啟動(dòng)了線程B，那么A、B是彼此獨(dú)立執(zhí)行的線程。若想終止線程A的同一時(shí)候強(qiáng)力終止線程B。一個(gè)簡單的方法是通過在線程A中調(diào)用B.setDaemon(True)實(shí)現(xiàn)。

但這樣帶來的問題是：線程B中的資源（打開的文件、傳輸數(shù)據(jù)等）可能會沒有正確的釋放。所以setDaemon()并不是一個(gè)好方法,更為妥當(dāng)?shù)姆绞绞峭ㄟ^Event機(jī)制。以下這段程序體現(xiàn)了setDaemon()和Event機(jī)制終止子線程的差別。

import threading 
import time 
class mythread(threading.Thread): 
 def __init__(self,stopevt = None,File=None,name = 'subthread',Type ='event'): 
  threading.Thread.__init__(self) 
  self.stopevt = stopevt 
  self.name = name 
  self.File = File 
  self.Type = Type 
   
     
 def Eventrun(self): 
  while not self.stopevt.isSet(): 
   print self.name +' alive\n' 
   time.sleep(2) 
  if self.File: 
   print 'close opened file in '+self.name+'\n' 
   self.File.close() 
  print self.name +' stoped\n' 
  
 def Daemonrun(self): 
  D = mythreadDaemon(self.File) 
  D.setDaemon(True) 
  while not self.stopevt.isSet(): 
   print self.name +' alive\n' 
   time.sleep(2) 
  print self.name +' stoped\n' 
 def run(self): 
  if self.Type == 'event': self.Eventrun() 
  else: self.Daemonrun() 
class mythreadDaemon(threading.Thread): 
 def __init__(self,File=None,name = 'Daemonthread'): 
  threading.Thread.__init__(self) 
  self.name = name 
  self.File = File 
 def run(self): 
  while True: 
   print self.name +' alive\n' 
   time.sleep(2) 
  if self.File: 
   print 'close opened file in '+self.name+'\n' 
   self.File.close() 
  print self.name +' stoped\n' 
   
def evtstop(): 
 stopevt = threading.Event() 
 FileA = open('testA.txt','w') 
 FileB = open('testB.txt','w') 
 A = mythread(stopevt,FileA,'subthreadA') 
 B = mythread(stopevt,FileB,'subthreadB') 
 print repr(threading.currentThread())+'alive\n' 
 print FileA.name + ' closed?
 '+repr(FileA.closed)+'\n' 
 print FileB.name + ' closed? '+repr(FileB.closed)+'\n' 
 A.start() 
 B.start() 
 time.sleep(1) 
 print repr(threading.currentThread())+'send stop signal\n' 
 stopevt.set() 
 A.join() 
 B.join() 
 print repr(threading.currentThread())+'stoped\n' 
 print 'after A stoped, '+FileA.name + ' closed? '+repr(FileA.closed)+'\n' 
 print 'after A stoped, '+FileB.name + ' closed?

 '+repr(FileB.closed)+'\n' 
def daemonstop(): 
 stopevt = threading.Event() 
 FileA = open('testA.txt','r') 
 A = mythread(stopevt,FileA,'subthreadA',Type = 'Daemon') 
 print repr(threading.currentThread())+'alive\n' 
 print FileA.name + ' closed?

 '+repr(FileA.closed)+'\n' 
 A.start() 
 time.sleep(1) 
 stopevt.set() 
 A.join() 
 print repr(threading.currentThread())+'stoped\n' 
 print 'after A stoped, '+FileA.name + ' closed? '+repr(FileA.closed)+'\n' 
 if not FileA.closed: 
  print 'You see the differents, the resource in subthread may not released with setDaemon()' 
  FileA.close() 
if __name__ =='__main__': 
 print '-------stop subthread example with Event:----------\n' 
 evtstop() 
 print '-------Daemon stop subthread example :----------\n' 
 daemonstop()

執(zhí)行結(jié)果是：

-------stop subthread example with Event:---------- 
<_MainThread(MainThread, started 2436)>alive 
testA.txt closed?
 False 
testB.txt closed? False 
subthreadA alive 
subthreadB alive 
 
<_MainThread(MainThread, started 2436)>send stop signal 
close opened file in subthreadA 
close opened file in subthreadB 
 
subthreadA stoped 
subthreadB stoped 
 
<_MainThread(MainThread, started 2436)>stoped 
after A stoped, testA.txt closed? True 
after A stoped, testB.txt closed?

 True 
-------Daemon stop subthread example :---------- 
<_MainThread(MainThread, started 2436)>alive 
testA.txt closed?

 False 
subthreadA alive 
subthreadA stoped 
<_MainThread(MainThread, started 2436)>stoped 
after A stoped, testA.txt closed? False 
You see the differents, the resource in subthread may not released with setDaemon()

總結(jié)

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