Proper way to kill child processes

[Jean Brouwers]

Another issue *might* be that the TERM signal is passed to the Pyton
process but ignored on Solaris.  Try using a different signal like
SIGQUIT or maybe even SIGKILL.  The shell process and all its child
processes should be terminated, by convention on *nix.  Also on RedHat
Linux it works.

There may be secondary issue with killing processes created by
popen2.Popen3().  The exit status of the child processes should be
checked to avoid zombies.  After killing a child process do call the
wait() or poll() method.  The wait() methods will wait forever and may
cause the parent process to hang.  To avoid that use poll() in a loop
until the return value is non-negative.  The sample code below may
help.

In any case, do use the list format for the cmd.  That is better if
there is no compelling need for the intermediate shell process.

/Jean Brouwers
 ProphICy Semiconductor, Inc.

PS) Sample code to avoid zombie (on *nix):

<pre>
  p = self.popen
  os.kill(p.pid, signal.SIGTERM)
  t = 2.5  # max wait time in secs
  while p.poll() < 0:
      if t > 0.5:
          t -= 0.25
          os.sleep(0.25)
      else:  # still there, force kill
          os.kill(p.pid, signal.SIGKILL)
          os.sleep(0.5)
          p.poll() # final try
          break
</pre>



In article <mailman.10.1087331713.21521.python-list at python.org>, Bob
Swerdlow <rswerdlow at transpose.com> wrote:

> My application starts up a number of processes for various purposes using:
>     self.popen = popen2.Popen3("/usr/local/bin/python -O "myscript.py")
> and then shuts them down when appropriate with
>     os.kill(self.popen.pid, signal.SIGTERM)
> Everything works fine on MacOSX.  However, I'm doing a port to Solaris (so I
> can run it on my web site) and find that the child processes are not
> stopping!  Solaris is creating TWO new processes: one for the SHELL and then
> another started by the shell to run my Python script.  The os.kill() is
> killing the shell process, not the one running my Python code.
> 
> Actually, I really want to kill both of these processes, but I only have the
> pid for the shell process.  I cannot kill the whole process group because
> that kills the main process, too (I tried it).
> 
> So, what is the best way to kill both the shell process (whose pid is
> available from the Popen3 object) and its child process that is running my
> Python script?  It looks like the python script process id is always one
> greater than the shell process id of the shell process,  but I'm sure I
> cannot rely on that.
> 
> Thanks,
> 
> Bob Swerdlow
> COO
> Transpose
> rswerdlow at transpose.com
> 207-781-8284
> http://www.transpose.com
> 
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