bug#59021: Unbounded heap growth when combining dynamic states & delimited continuation

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hi Ludovic,

Ludovic Courtès <ludo@gnu.org> writes:

> (This is a followup to <https://github.com/wingo/fibers/issues/65>,
> itself a followup to <https://issues.guix.gnu.org/58631>.)
>
> Consider this code:
>
> ;; https://issues.guix.gnu.org/58631
> ;; https://github.com/wingo/fibers/issues/65
>
> (define loss
>   (make-vector 1000000))
>
> (let ((tag (make-prompt-tag "my prompt")))
>   (define handler
>     (lambda (k i)
>       (when (zero? (modulo i 2000000))
>         (pk 'heap-size (assoc-ref (gc-stats) 'heap-size)))
>
>       (call-with-prompt tag
>         (lambda ()
>           (k (modulo (+ 1 i) 10000000)))
>         handler)))
>
>   (call-with-prompt tag
>     (let ((state (current-dynamic-state)))
>       (lambda ()
>         ;; (define (with-dynamic-state state thunk)
>         ;;   (let ((previous #f))
>         ;;     (dynamic-wind
>         ;;       (lambda () (set! previous (set-current-dynamic-state state)))
>         ;;       thunk
>         ;;       (lambda () (set-current-dynamic-state previous)))))
>         (with-dynamic-state state
>                             (lambda ()
>                               (let loop ((i 0))
>                                 (loop (abort-to-prompt tag i)))))))
>     handler))
>
> On Guile 3.0.8, this program exhibits seemingly unbounded heap growth.
> Uncommenting the local ‘with-dynamic-state’ definition fixes the
> problem.

I've tested both 3.0.8 from Guix on multiple machines (including Berlin)
and 2.2 from Debian 10, and ran the above snippet; it grows initially
but stabilize quickly and then doesn't budge.  I've let it run for more
than an hour.

So there's a problem there (?), but it doesn't seem like an unbound leak
from my experiments.  Perhaps the reproducer needs to be tweaked to
mimic better what is happening in Shepherd?

-- 
Thanks,
Maxim