Re: GOOPS and fibers - need help understanding what's wrong, bug in fibers/guile?

[Chris Vine]

On Wed, 22 Jul 2020 01:56:53 +0200
Jan Wielkiewicz <tona_kosmicznego_smiecia@interia.pl> wrote:
> Hello,
> 
> I started writing my project in Guile with GOOPS and fibers (I'll
> release it once it stops being a shame and starts working!), but I
> encountered a problem:
> 
> The example from fibers' manual doesn't work:
> 
> (lambda ()
>  (spawn-fiber (lambda () (display "hey!\n")))))
> 
> It doesn't print "hey" as documented in the manual.
> I use guile 3.0.4 and fibers 1.0.0 (from Guix).

(You are missing '(run-fibers' at the beginnng.  Presumably this was
just a pasting error on your part.)

With that omission corrected, it used to work with guile-2.2.  Something
seems to have changed with guile-3.0, because it only works for me with
guile-3.0 if you set #:drain? to #t in the call to run-fibers.  Without
that, run-fibers appears to return before init-thunk returns.

So it seems that there is either a bug in the manual or in the fibers
implementation, probably the latter.

> I also tried making a simple proof of concept, but it doesn't seem to
> do anything. I would like to understand what's wrong with my code or
> report a bug, if this is the case. No errors, warnings, syntax errors,
> just silence.
> 
> My code:
> 
> (define-module (blocks block)
>   #:use-module (fibers)
>   #:use-module (fibers channels)
>   #:use-module (oop goops)
>   #:use-module (srfi srfi-9) ;; records
>   #:export (<peer>
>             connect-peers
>             send-message
>             handle-message
>             start-listening))
> 
> (define-class <peer> ()
>   (input #:init-form '() #:getter get-input
>          #:setter set-input #:init-keyword #:input)
>   (output #:init-form '() #:getter get-output
>           #:setter set-output #:init-keyword #:output))
> 
> ;; Only connection, no messaging started.
> (define-method (connect-peers (p1 <peer>) (p2 <peer>))
>   (let ((p1-p2 (make-channel)) ;; p1 to p2
>         (p2-p1 (make-channel))) ;; p2 to p1
>     (set-input p1 p2-p1)
>     (set-output p1 p1-p2)
>     (set-input p2 p1-p2)
>     (set-output p2 p2-p1)))
> 
> (define-method (send-message (p <peer>) msg)
>   (put-message (get-output p) msg))
> 
> (define-method (handle-message (p <peer>))
>   (let loop ()
>     (define msg (get-message (get-input p)))
>     (match (pk msg)
>            ('ping (send-message p 'pong)))
>     (loop)))
> 
> (define-method (start-listening (p1 <peer>) (p2 <peer>))
>   (run-fibers
>    (lambda ()
>      (spawn-fiber
>       (lambda ()
>         (connect-peers p1 p2)
>         (handle-message p1)
>         (send-message p1 'ping)
>         (handle-message p2))))))
> 
> I run this in repl:
> 
> (define p1 (make <peer>))
> (define p2 (make <peer>))
> 
> (start-listening p1 p2)

TL;DR, and I do not either like or use GOOPS, so I am not sure what you
are doing anyway. But try setting #:drain? to #t.

Chris