python/57429.html">python/270780.html">python/291754.html">python/270985.html">python/284159.html">python主要是通過thread和threading這兩個模塊來實現多線程支持。
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。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模塊(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，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，在多個線程間切換所需的時間很多其它，占用資源也更少。
通過threading模塊創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對象一個可運行方法（或對象）;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()啟動的線程彼此是獨立的。若在線程A中啟動了線程B，那么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在線程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（打開的文件、傳輸數據等）可能會沒有正確的釋放。所以setDaemon()并不是一個好方法,更為妥當的方式是通過Event機制。以下這段程序體現了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()
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