name 'aLOCK' is not defined When I add aLOCK = threading.RLock() behind if __name__ == "__main__"

[MRAB]

On 2018-08-09 16:16, xuanwu348 wrote:
> Hi team
> 
> Good day
> The problem I meet when I add "aLOCK = threading.RLock()" to PositionB, the program will report error "name 'aLOCK' is not defined ",
> but when I change this code to PositionA, it can run normally, is there any difference for the code between 'if __name__ == "__main__:"', can you help me, thanks!
> 
> The file I was attached, please change the extend ".pyx" to ".py", thanks, code as below, tried python2.7 and python3.4:
> 
> import threading
> import time
> from multiprocessing import Process
> 
> #PositionA
> aLOCK = threading.RLock()
> 
> def Save_runnedCMD(filename, strings):
>      aLOCK.acquire()
>      with open(filename, "at") as f:
>          f.write(str(strings) + "\n\r")
>      aLOCK.release()
> 
> def runCMD(filename):
>      time.sleep(1)
>      cmd = "testtest"
>      Save_runnedCMD(filename, cmd)
> 
> 
> def Thr_run(filename):
>      t = []
>      for i in range(2):
>          tt = threading.Thread(target = runCMD, args=(filename,))
>          tt.start()
>          t.append(tt)
>      for tt in t:
>          tt.join()
> 
> if __name__ == "__main__":
>      filename = "./testaaaaa.log"
> 
>      #PositionB
>      #aLOCK = threading.RLock()
> 
>      while 1:
>          t1 = Process(target=Thr_run, args=(filename, ))
>          t1.start()
>          t1.join()
> 
> Error info as below:
> D:\Appppp>python testa.py
> Exception in thread Thread-1:
> Traceback (most recent call last):
>    File "C:\Python34\lib\threading.py", line 921, in _bootstrap_inner
>      self.run()
>    File "C:\Python34\lib\threading.py", line 869, in run
>      self._target(*self._args, **self._kwargs)
>    File "D:\Appppp\testa.py", line 15, in runCMD
>      Save_runnedCMD(filename, cmd)
>    File "D:\Appppp\testa.py", line 7, in Save_runnedCMD
>      aLOCK.acquire()
> NameError: name 'aLOCK' is not defined
> 
> Exception in thread Thread-2:
> Traceback (most recent call last):
>    File "C:\Python34\lib\threading.py", line 921, in _bootstrap_inner
>      self.run()
>    File "C:\Python34\lib\threading.py", line 869, in run
>      self._target(*self._args, **self._kwargs)
>    File "D:\Appppp\testa.py", line 15, in runCMD
>      Save_runnedCMD(filename, cmd)
>    File "D:\Appppp\testa.py", line 7, in Save_runnedCMD
>      aLOCK.acquire()
> NameError: name 'aLOCK' is not defined
> 
When you run the script, __name__ will be "__main__".

When script uses the multiprocessing module to run the function 
"Thr_run" in another process, it actually starts another instance of 
itself, and in that other instance, name _won't_ be "__main__".

Here's a simple example:


from multiprocessing import Process

def test_func():
     print('test_func')

print('__name__ is {!a}'.format(__name__))

if __name__ == "__main__":
     p = Process(target=test_func)
     p.start()
     p.join()


When run, it prints:


__name__ is '__main__'
__name__ is '__mp_main__'
test_func


So, if you put the lock at PositionB, it won't be created by the subprocess.