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，可以更加方便的被使用。但是python（cpython）由於GIL的存在無法使用threading充分利用CPU資源，如果想充分發揮多核CPU的計算能力需要使用multiprocessing模塊(Windows下使用會有諸多問題)。
如果在對線程應用有較高的要求時可以考慮使用Stackless Python來完成。Stackless Python是Python的一個修改版本，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更多，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對象一個可執行方法（或對象）;第二種是繼承threading.Thread定義子類並重寫run()方法。第二種方法中，唯一必須重寫的方法是run()，可根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__()必須要在函數第一行調用，否則會觸發錯誤“AssertionError: Thread.__init__() not called”
Python threading模塊不同於其他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，若在線程A中啟動了線程B，那麼A、B是彼此獨立運行的線程。若想終止線程A的同時強力終止線程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、數據傳輸等）可能會沒有正確的釋放。所以setDaemon()並非一個好方法,更為妥當的方式是通過Event機制。下面這段程序體現了setDaemon()和Event機制終止子線程的區別。
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()
運行結果是：
-------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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