GNU bug report logs - #27553
[PATCH shepherd] Register SIGCHLD handler after primitive fork

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: ludo <at> gnu.org (Ludovic Courtès)
Cc: tracker <at> debbugs.gnu.org
Subject: bug#27553: closed ([PATCH shepherd] Register SIGCHLD handler
 after primitive fork)
Date: Thu, 07 Sep 2017 14:50:02 +0000

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Your message dated Thu, 07 Sep 2017 16:49:36 +0200
with message-id <87o9qmtvgf.fsf <at> gnu.org>
and subject line Re: [bug#27553] [PATCH shepherd] Register SIGCHLD handler after primitive fork
has caused the debbugs.gnu.org bug report #27553,
regarding [PATCH shepherd] Register SIGCHLD handler after primitive fork
to be marked as done.

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help-debbugs <at> gnu.org.)


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From: Jelle Licht <jlicht <at> fsfe.org>
To: guix-patches <at> gnu.org
Subject: [PATCH shepherd] Register SIGCHLD handler after primitive fork
Date: Sun, 2 Jul 2017 03:11:01 +0200

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Hi all,

I am not sure if this is also the proper ML for the GNU Shepherd, but
looking in the archives lead me to believe it actually is. If not, I
suggest the gnu.org page for shepherd be updated with the correct info.

I recently starting playing around with user shepherd, and found out that
when running a shepherd 0.3.2 daemonized as non-init process (via "(action
'shepherd 'daemonize)"), zombie processes are created whenever you start
and subsequently stop any service.

Thinking I did something wrong, I asked lfam on #guix to share his (very
helpful) init.scm for user shepherd, yet I still noticed the same behaviour.

I believe commit `efa2f45c5f7dc735407381b7b8a83d6c37f828db' inadvertently
introduced an ordering issue, where the SIGCHLD handler is registered
/before/ shepherd has the chance to daemonize. I believe the following
trivial patch addresses this snafu.

Regards,
Jelle

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[0001-Register-SIGCHLD-handler-after-primitive-fork.patch (text/x-patch, attachment)]

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From: ludo <at> gnu.org (Ludovic Courtès)
To: Jelle Licht <jlicht <at> fsfe.org>
Cc: 27553-done <at> debbugs.gnu.org
Subject: Re: [bug#27553] [PATCH shepherd] Register SIGCHLD handler after
 primitive fork
Date: Thu, 07 Sep 2017 16:49:36 +0200

Heya!

Jelle Licht <jlicht <at> fsfe.org> skribis:

> I just tested what Ludo' proposed, and it seems to work like a charm.
> Seeing as we might be seeing more non-init shepherd instances w.r.t.
>  user services and the possible service extension to `guix environment',
> I think it would be a good call to fix this bug :-).

Indeed, thanks for the reminder.

> From db942182224dfc0accad94897dd2122b128eef07 Mon Sep 17 00:00:00 2001
> From: Jelle Licht <jlicht <at> fsfe.org>
> Date: Thu, 7 Sep 2017 00:52:49 +0200
> Subject: [PATCH] Lazily register SIGCHLD hander on first call to
>  'fork+exec-command'.
>
> * modules/shepherd.scm (main): Move unconditional top-level call to 'sigaction' to...
> * modules/shepherd/service.scm (fork+exec-command): here. Use new variable.
> (%sigchld-handler-installed?): New variable.

LGTM, applied!

Ludo’.

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