Re: The Shepherd on Fibers

[Ludovic Courtès]

Maxime Devos <maximedevos@telenet.be> skribis:

> 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?

The short answer is that I want to get that done and not rely on an
unreleased version of Fibers.  The hack above uses the public interface;
it’s not pretty, but I think it’s okay.

Longer-term, maybe we could change Fibers’ ‘sleep’ as you suggest.
Whether it’s a good idea is debatable: one could argue that Fibers’
‘sleep’ is meant to be called from a fiber (suspendable).

Ludo’.