bug#31925: 'guix substitutes' sometimes hangs on glibc 2.27

[Andy Wingo <wingo@igalia.com>]

On Thu 05 Jul 2018 14:27, ludo@gnu.org (Ludovic Courtès) writes:

> Hello,
>
> Andy Wingo <wingo@igalia.com> skribis:
>
>> The signal thread is a possibility though in that case you'd get a
>> warning; the signal-handling thread appears in scm_all_threads.  Do you
>> see a warning?  If you do, that is a problem :)
>
> I don’t see a warning.
>
> But as a Guile user, I shouldn’t see a warning just because there’s a
> signal thread anyway; it’s not a thread I spawned myself.

I understand but it's how it works.  If we want to change this, probably
we need a similar interface as we have with finalization.

> The weird thing is that the signal thread always exists, and it’s
> surprising IMO that it shows up in ‘scm_all_threads’ because it’s not a
> “user thread”.  The other surprise is that the warning isn’t triggered:
>
> $ guile
> GNU Guile 2.2.4
> Copyright (C) 1995-2017 Free Software Foundation, Inc.
>
> Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
> This program is free software, and you are welcome to redistribute it
> under certain conditions; type `,show c' for details.
>
> Enter `,help' for help.
> scheme@(guile-user)> (all-threads)
> $1 = (#<thread 140488743438080 (1b06c40)> #<thread 140488815434624 (1b06e00)>)
> scheme@(guile-user)> (when (zero? (primitive-fork)) (primitive-_exit 0))
> ;; no warning

Are you certain that this is the signal-handling thread and not the
finalizer thread?  I suspect it is the finalizer thread, and that it
gets properly shut down before the fork.

Regarding seeing the warning: do you do make some other binding for the
default warning port in Guix?

Andy