Python線程建立和終止執行個體代碼，python線程終止執行個體

Python線程建立和終止執行個體代碼，python線程終止執行個體

python主要是通過thread和threading這兩個模組來實現多線程支援。

python的thread模組是比較底層的模組，python的threading模組是對thread做了一些封裝，能夠更加方便的被使用。可是python（cpython）因為GIL的存在無法使用threading充分利用CPU資源，假設想充分發揮多核CPU的計算能力須要使用multiprocessing模組(Windows下使用會有諸多問題)。

假設在對線程應用有較高的要求時能夠考慮使用Stackless Python來完畢。Stackless Python是Python的一個改動版本號碼，對多線程編程有更好的支援，提供了對微線程的支援。微線程是輕量級的線程，在多個線程間切換所需的時間很多其它，佔用資源也更少。

通過threading模組建立新的線程有兩種方法：一種是通過threading.Thread(Target=executable Method)-即傳遞給Thread對象一個可運行方法（或對象）;另外一種是繼承threading.Thread定義子類並重寫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__()必需要在函數第一行調用，否則會觸發錯誤“AssertionError: Thread.__init__() not called”

Python threading模組不同於其它語言之處在於它沒有提供線程的終止方法，通過Python threading.Thread()啟動的線程彼此是獨立的。若線上程A中啟動了線程B，那麼A、B是彼此獨立執行的線程。若想終止線程A的同一時候強力終止線程B。一個簡單的方法是通過線上程A中調用B.setDaemon(True)實現。

但這樣帶來的問題是：線程B中的資源（開啟的檔案、傳輸資料等）可能會沒有正確的釋放。所以setDaemon()並不是一個好方法,更為妥當的方式是通過Event機制。以下這段程式體現了setDaemon()和Event機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() 

執行結果是：

-------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

以上就是本文關於Python線程建立和終止執行個體代碼的全部內容，希望對大家有所協助。感興趣的朋友可以繼續參閱本站其他相關專題，如有不足之處，歡迎留言指出。感謝朋友們對本站的支援！