The Python thread creates and terminates the instance code

python is mainly through thread and threading modules to achieve multithreading support.

The thread module of python is the underlying module, while the threading module of python is some encapsulation of thread, which can be used more conveniently. However, python (cpython) cannot make full use of CPU resources due to the existence of GIL, so it is assumed that the full use of multi-core CPU computing power requires the use of multiprocessing module (there will be many problems under Windows).

Suppose you can consider using Stackless Python when you have high requirements for threaded applications. Stackless Python is a modified version of Python with better support for multithreaded programming and support for tasklets. Tasklets are lightweight threads that take a lot more time to switch between threads and consume less resources.

There are two ways to create a new thread through the threading module: one is via ES29en. Thread(Target=executable Method) -- that is, pass a runnable method (or object) to the Thread object; The other is to inherit the threading.Thread definition subclass and override the run() method. Of the other method, the only method with which 1 must be overridden is run(), and can be rewritten as needed. It's worth noting that, to rewrite ___ 40en__ (), the parent class of ___ must be called at line 1 of the function, otherwise the error "AssertionError: Thread. 44en__ () not called" will be triggered.

The Python threading module is different from other languages in that it does not provide a method for terminating threads, and threads started through Python ES52en.Thread () are independent of each other. If thread B is started in thread A, then A and B are threads executing independently of each other. Force terminates thread B at the same time as you want to terminate thread A. An easy way to do this is by calling B.setDaemon (True) from thread A.

The problem with this is that the resources in thread B (open files, transferred data, etc.) may not be released correctly. Therefore, setDaemon() is not a good method, and a more appropriate way is through the Event mechanism. The following program illustrates the difference between the setDaemon() and Event mechanisms for terminating child threads.

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() 

The execution results are:

-------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() 

conclusion

That's it for the Python thread creation and termination instance code. Interested friends can continue to refer to other related topics in this site, if there is any deficiency, welcome to comment out. Thank you for your support!