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bug#63190: [Shepherd] Nested calls lead to a hang
From: |
Ludovic Courtès |
Subject: |
bug#63190: [Shepherd] Nested calls lead to a hang |
Date: |
Sat, 13 May 2023 11:45:51 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) |
Brian Cully <bjc@spork.org> skribis:
> Ludovic Courtès <ludo@gnu.org> writes:
>
>> (Whether that leads to a deadlock depends; at first sight, I’d say
>> there’s no reason for this to deadlock in general, but you can of
>> course
>> end up with a logic bug like A starts B, which spawns a client to
>> start
>> A, which doesn’t start because it’s waiting for B.)
>
> It's been a while since I looked at this, but my rough recollection is
> the deadlock occurs because shepherd can only process one request over
> its socket at a time.
That’s not the case in 0.9: it can process several requests
concurrently. However, as I wrote in a followup message, the client
socket created by (gnu services herd) lacks SOCK_NONBLOCK, which can
thus block the process on reads and writes.
Ludo’.