Am 03.01.2012 14:40, schrieb Adam Skutt:
On Jan 3, 7:31 am, Heiko Wundram<modeln...@modelnine.org> wrote:
Yes, it can be avoided, that's what the default SIGCHLD-handling
(keeping the process as a zombie until it's explicitly collected by a
wait*()) is for, which forces the PID not to be reused by the operating
system until the parent has acknowledged (by actively calling wait*())
that the child has terminated.
No, you still can see ESRCH when sending signals to a zombie process.
Code that sends signals to child processes via kill(2) must be
prepared for the call to fail at anytime since the process can die at
anytime. It can't handle the signal, so it's treated as if it doesn't
exist by kill(2) in this case. However, you don't have to worry about
sending the signal to the wrong process.
Getting an error on kill (which you can catch) is not about the race
that the posters were speculating about (i.e., sending the signal to the
wrong process), and that's what I was trying to put straight. The only
advice that I wanted to give is:
1) before calling wait to collect the child, call kill as much as you
like, and in case it errors, ignore that,
2) after calling wait, never, ever kill, and you don't need to, because
you already know the process is gone.
There's no race possibility in this, _except_ if you alter handling of
SIGCHLD away from the default (i.e., to autocollect children), in which
case you have the possibility of a race and shooting down unrelated
processes (which the discussion was about).
--
--- Heiko.
--
http://mail.python.org/mailman/listinfo/python-list
