From mboxrd@z Thu Jan  1 00:00:00 1970
From: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Subject: bug#34033: Offloading sometimes hangs
Date: Fri, 21 Feb 2020 23:37:06 -0500
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In-Reply-To: <87fttuq2mz.fsf@gnu.org> ("Ludovic
 \=\?utf-8\?Q\?Court\=C3\=A8s\=22'\?\=
 \=\?utf-8\?Q\?s\?\= message of "Mon, 14 Jan 2019 23:45:56 +0100")
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To: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Cc: 34033@debbugs.gnu.org

Hello Ludovic,

Ludovic Court=C3=A8s <ludo@gnu.org> writes:

> Hello,
>
> Ludovic Court=C3=A8s <ludo@gnu.org> skribis:
>
>> A simple thing would be to somehow get libssh to pass POLLIN | POLLRDHUP
>> instead of just POLLIN.
>
> Reported here:
>
>   https://www.libssh.org/archive/libssh/2019-01/0000000.html
>
> A fix has been proposed by upstream and should be committed shortly.
>
>> Additionally, we could change Guile-SSH so that we can specify a timeout
>> when reading from a channel.
>
> Turns out we can set a per-session timeout, which we already do (see
> #:timeout in =E2=80=98open-ssh-session=E2=80=99 in (guix scripts offload)=
) but
> =E2=80=98ssh_channel_read=E2=80=99 would ignore it and instead pass an in=
finite timeout
> to poll(2):
>
>   https://www.libssh.org/archive/libssh/2019-01/0000001.html
>
> This issue happens to be fixed in libssh 0.8.x, so I upgraded our libssh
> package in commit a8b0556ea1e439c89dc1ba33c8864e8b9b811f08.
>
> (That still doesn=E2=80=99t tell us why our =E2=80=98guix offload=E2=80=
=99 processes would
> occasionally be stuck but at least it ensures the build farm keeps
> making progress even when that happens.)
>
> Ludo=E2=80=99.

Seems the patch in the response at the URL you linked is awaiting some
feedback/review.  Is this the reason 'guix substitute' hangs for so long
when the substitute server is down? (like 1 minute or so).

Maxim