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So I have a python script that runs a loop in which it calls a program A through subprocess.Popen waits for its output, then saves the output and then calls it again and so on. (This keeps happening for a number of runs I set as an input)

The thing is that I have a timer so that whenever the program A takes more than a particular threshold_time, the script kills the process with process.kill() and moves on to the next iteration.

The problem is that even though everything seems to work fine even for 300 runs, sometimes I get this error: 

    File "C:\Python27\lib\subprocess.py", line 1002, in terminate
    _subprocess.TerminateProcess(self._handle, 1)
    WindowsError: [Error 5] Access is denied

and then the script dies.

The referred script part:

timeout = TIME_CONST
for run in runs:
    killed = False
    start = time.clock()
    p = subprocess.Popen("SOME.CMD", cwd=r"some_dir") 
    # Monitor process. If it hits threshold, kill it and go to the next run
    while p.poll() is None:
        time.sleep(20) 
        secs_passed = time.clock() - start

        ### the following was my initial buggy line ###
        #if secs_passed >= timeout: 

        ### corrected line after jedislight's answer ###
        #if the time is over the threshold and process is still running, kill it
        if secs_passed >= timeout and p.poll is None: 
            p.kill()
            killed = True  
            break
    if killed: continue

Do you have any suggestions what the problem might be?

EDIT: Accepted answer and fixed the code. Thanks @jedislight for your feedback!

Galois
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  • Can you post the smallest Python script that can reproduce this behavior? – Sridhar Ratnakumar Apr 07 '11 at 00:13
  • @Sridhar I added the code you asked for. – Galois Apr 08 '11 at 03:11
  • I tried it with "SOME.CMD" being just "cmd" and it worked. What is your process you are trying to kill? – Fenikso Apr 13 '11 at 07:27
  • This can happen if the process is doing something with elevated privileges. Assuming your local administrator account is called Admin, `subprocess.Popen("runas /user:Admin cmd.exe")` will probably raise the same exception if you provide the password before the script tries to kill it. – robots.jpg Jun 01 '11 at 20:47

1 Answers1

8

You are seperating your p.poll() and your p.kill() by 20 seconds. By then the process could have finished. I would suggest moving the time.sleep(20) call around so that you poll and kill happen in the same time frame, to avoid killing a dead process. Below is an example run in iPython showing a similar error when killing a completed process:

In [2]: import subprocess

In [3]: p = subprocess.Popen("dir")

In [4]: p.poll()
Out[4]: 0

In [5]: p.kill()
---------------------------------------------------------------------------
WindowsError                              Traceback (most recent call last)

C:\Users\---\<ipython console> in <module>()

C:\Python26\lib\subprocess.pyc in terminate(self)
    947             """Terminates the process
    948             """
--> 949             _subprocess.TerminateProcess(self._handle, 1)
    950
    951         kill = terminate

WindowsError: [Error 5] Access is denied

Even if you kill directly after a poll that shows the processes is running it can finish before the next line is executed. I would also suggest adding a try-catch block for this exception and if it occurs poll again to see if the process actually completed.

jedislight
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