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[debbugs-tracker] bug#9488: closed (23.2; `call-process' races with SIGC

From: GNU bug Tracking System
Subject: [debbugs-tracker] bug#9488: closed (23.2; `call-process' races with SIGCHLD handler)
Date: Mon, 03 Dec 2012 21:51:03 +0000

Your message dated Mon, 03 Dec 2012 13:47:59 -0800
with message-id <address@hidden>
and subject line Re: 24.3.50; Zombie process left after call-process
has caused the debbugs.gnu.org bug report #9488,
regarding 23.2; `call-process' races with SIGCHLD handler
to be marked as done.

(If you believe you have received this mail in error, please contact

9488: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=9488
GNU Bug Tracking System
Contact address@hidden with problems
--- Begin Message --- Subject: 23.2; `call-process' races with SIGCHLD handler Date: Mon, 12 Sep 2011 20:14:11 +0000 User-agent: IMAIL/1.21; Edwin/3.116; MIT-Scheme/9.1
`call-process' relies on `wait_for_termination' to block until the
SIGCHLD handler has run for the synchronous subprocess.  But this is
not the condition that `wait_for_termination' guarantees on exit.
Rather, if `wait_for_termination' returns, then either

(a) there is no process having the same pid as the child had, or
(b) a SIGCHLD has been delivered.

If the subprocess has died, but no SIGCHLD has been delivered yet,
then `wait_for_termination' may return even though the SIGCHLD handler
has yet to run.  As an aside, these conditions are not sufficient for
`wait_for_termination' to return: it may block indefinitely if the
operating system has already delivered SIGCHLD and reused the pid
before control enters `wait_for_termination'.  I have not observed
indefinite blocking behaviour in practice, but only because pids don't
get reused very fast.

What I have observed is process exit values of 0 that should have been
nonzero on

GNU Emacs 23.2.1 (i386--netbsdelf, X toolkit) of 2011-03-02.

I noticed this because `M-x grep' sometimes prompts me with `grep -nH'
and sometimes with `grep -nH -e', in turn because

(call-process "grep" nil nil nil "-e" "/dev/null")

sometimes returns 0 and sometimes returns 1 depending on who wins the

I have not tested newer versions of GNU Emacs, but a cursory glance at
the code suggests that while the relevant subprocess code has grown
more unmaintainably complicated, the problem persists.

--- End Message ---
--- Begin Message --- Subject: Re: 24.3.50; Zombie process left after call-process Date: Mon, 03 Dec 2012 13:47:59 -0800 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0
No further comment, so I installed the patch as Emacs trunk bzr 111081
and am marking bugs 9488 and 12980 as done.

--- End Message ---

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