From: ludo@gnu.org (Ludovic Courtès)
To: Carlo Zancanaro <carlo@zancanaro.id.au>
Cc: 30637@debbugs.gnu.org
Subject: [bug#30637] [WIP] shepherd: Poll every 0.5s to find dead forked services
Date: Wed, 28 Feb 2018 23:06:06 +0100 [thread overview]
Message-ID: <87y3jcu5v5.fsf@gnu.org> (raw)
In-Reply-To: <878tbe9jvx.fsf@zancanaro.id.au> (Carlo Zancanaro's message of "Wed, 28 Feb 2018 08:56:34 +1100")
Hi Carlo,
Carlo Zancanaro <carlo@zancanaro.id.au> skribis:
> Another patch for shepherd!
Always welcome! :-)
> The problem is that shepherd, when run as a user process, can "lose"
> services which fork away. Shepherd can still kill them, but a SIGCHLD
> won't be delivered if they die, so shepherd can't restart/disable
> them. My prime example is emacs, which I run with --daemon. If I then
> kill emacs, shepherd will still think that it is running.
There are two issues here, I think.
1. shepherd cannot lose SIGCHLD: if a process dies immediately once
it’s been spawned, as is the case with “emacs --daemon” or any
other daemon-style program, it should receive SIGCHLD and process
it.
However, there could be a race condition: if SIGCHLD is handled
before the ‘running’ value has been set, then we’ll still get the
non-#f ‘running’ value even though the process died in the
meantime.
The code tries to prevent that (see (shepherd service) around line
320), but looking more closely, I think the race is still there.
Namely, the whole ‘let’ block, including the call to ‘start’,
should be in ‘call-with-blocked-asyncs’, I think. Could you check
if that helps for you?
2. shepherd currently can’t do much with real daemons. So what we do
in GuixSD is to either start programs in non-daemon mode, when
that’s an option, or pass #:pid-file to retrieve the forked process
PID. I think you should do one of these as well.
WDYT?
Thanks,
Ludo’.
next prev parent reply other threads:[~2018-02-28 22:07 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-27 21:56 [bug#30637] [WIP] shepherd: Poll every 0.5s to find dead forked services Carlo Zancanaro
2018-02-28 22:06 ` Ludovic Courtès [this message]
2018-03-01 22:37 ` Carlo Zancanaro
2018-03-02 9:44 ` Ludovic Courtès
2018-03-02 10:13 ` Carlo Zancanaro
2018-03-02 12:42 ` Ludovic Courtès
2018-03-03 7:58 ` Carlo Zancanaro
2018-03-03 15:21 ` Ludovic Courtès
2018-03-03 20:49 ` Carlo Zancanaro
2018-03-04 22:11 ` Ludovic Courtès
2018-03-04 22:35 ` Carlo Zancanaro
2018-03-04 22:49 ` Ludovic Courtès
2018-03-04 23:08 ` Carlo Zancanaro
2018-03-05 14:15 ` bug#30637: " Ludovic Courtès
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