Re: The Shepherd on Fibers

[Maxime Devos]

Ludovic Courtès schreef op wo 23-03-2022 om 23:36 [+0100]:
Thoughts?

From service.scm:

> +  (define (sleep* n)
> +    ;; In general we want to use (@ (fibers) sleep) to yield to the 
> scheduler.
> +    ;; However, this code might be non-suspendable--e.g., if the user calls
> +    ;; the 'start' method right from their config file, which is loaded with
> +    ;; 'primitive-load', which is a continuation barrier.  Thus, this variant
> +    ;; checks whether it can suspend and picks the right 'sleep'.
> +    (if (yield-current-task)
> +        (begin
> +          (set! sleep* (@ (fibers) sleep))
> +          (sleep n))
> +        (begin
> +          (set! sleep* (@ (guile) sleep))
> +          ((@ (guile) sleep) n))))

Instead of working around this limitation of Fiber's 'sleep',
why not modify Fiber's sleep to detect if it is from a suspendable
context or not, and depending on that, use Guile's sleep/usleep or
the perform-operation+sleep-operation?

Additionally, the set! can be avoided here in favour of a loop variable:

(define start ...)
(define (sleep n)
  ;; In general [...]
  (if (yield-current-task)
      (begin ((@ (fibers) sleep) n) ((@ (fibers) sleep) n))
      (begin ((@ (guile) sleep) n) ((@ (guile) sleep) n))))
(let loop ((sleep sleep))
  (define (try-again)
     ...
     
     (loop (sleep 1)))
  (catch ...))

FWIW, the delay can be decreased here, if Guile's sleep is replaced
by an appropriate use of 'usleep'.

Greetings,
Maxime.

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