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

[Chris Vine <vine35792468@gmail.com>]

On Wed, 22 Jul 2020 12:54:20 +0100
Chris Vine <vine35792468@gmail.com> wrote:
> 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.

On further reflection I am not sure if it did used to work with
guile-2.2.  I think it may be a bug in the manual after all.  This works
OK:

  (display (run-fibers
            (lambda ()
              (let ((channel (make-channel)))
                (spawn-fiber
                 (lambda ()
                   (sleep 1) ;; do some work
                   (put-message channel "hello world")))
                (simple-format #t "~a~%" (get-message channel))
                "finished\n"))))

The point about:

  (run-fibers
   (lambda () (spawn-fiber
               (lambda ()
                 (set! v "Set")
                 (display "hey!\n")))))

is that spawn-fiber, and so init-thunk, will return straigntaway with a
new fiber object.

So I suspect setting #:drain? to #t will resolve your problem.

It might be worth reporting the bug in the manual as an issue on the
github repository (assuming the above is correct).