From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@gnu.org>
Subject: Re: [PATCH] utils: Handle errors in worker threads.
Date: Wed, 05 Feb 2020 16:08:48 +0100
Message-ID: <87mu9xnkan.fsf@gnu.org>
References: <20200203192027.7944-1-mail@cbaines.net>
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In-Reply-To: <20200203192027.7944-1-mail@cbaines.net> (Christopher Baines's
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To: Christopher Baines <mail@cbaines.net>
Cc: guix-devel@gnu.org

Hi,

Christopher Baines <mail@cbaines.net> skribis:

> Previously, if an error occurred, the worker fiber simply never sends a
> reply. In the case of HTTP requests to Cuirass, where an exception occurs=
 when
> performing a database query, the fiber handling the request blocks as it =
never
> gets a response. I think that this has the potential to cause the process=
 to
> hit file descriptor limits, as the connections are never responded to.
>
> This is fixed by responding with the details of the exception, and then
> throwing it within the fiber that made the call.
>
> * src/cuirass/utils.scm (make-worker-thread-channel): Catch exceptions wh=
en
> calling proc.
> (call-with-worker-thread): Handle receiving exceptions from the worker th=
read.

Good catch!

> +                     (put-message reply
> +                                  (catch
> +                                    #t

Please put #t on the same line as =E2=80=98catch=E2=80=99.  :-)

> +                                    (lambda ()
> +                                      (apply proc args))
> +                                    (lambda (key . args)
> +                                      (cons* 'worker-thread-error key ar=
gs))))))

As discussed with others at the Guix Days, it=E2=80=99s probably a good ide=
a to
distinguish =E2=80=9Cremote=E2=80=9D exceptions from local exceptions like =
you did (and
unlike what =E2=80=98inferior-eval=E2=80=99 does).

LGTM!

Ludo=E2=80=99.