Re: [PATCH] utils: Handle errors in worker threads.

["Ludovic Courtès" <ludo@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 when
> calling proc.
> (call-with-worker-thread): Handle receiving exceptions from the worker thread.

Good catch!

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

Please put #t on the same line as ‘catch’.  :-)

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

As discussed with others at the Guix Days, it’s probably a good idea to
distinguish “remote” exceptions from local exceptions like you did (and
unlike what ‘inferior-eval’ does).

LGTM!

Ludo’.