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Subject: |
Unbounded heap growth when combining dynamic states & delimited continuation |
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Date: |
Fri, 04 Nov 2022 19:24:50 +0100 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.1 (gnu/linux) |
(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:
--8<---------------cut here---------------start------------->8---
;; 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))
--8<---------------cut here---------------end--------------->8---
On Guile 3.0.8, this program exhibits seemingly unbounded heap growth.
Uncommenting the local ‘with-dynamic-state’ definition fixes the
problem.
Ludo’.
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--- Begin Message ---
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Subject: |
Re: bug#59021: Unbounded heap growth when combining dynamic states & delimited continuation |
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Date: |
Sun, 20 Nov 2022 18:28:13 +0100 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) |
Hi,
Ludovic Courtès <ludo@gnu.org> skribis:
> Ludovic Courtès <ludo@gnu.org> skribis:
>
>> 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.
>
> This is fixed by the patch below (tested against the test case above and
> the Fibers and Shepherd test cases mentioned before):
Pushed as e47a153317c046ea5d335940412999e7dc604c33.
> Using a simple heap profiler (more on that later), I noticed that the
> stacks allocated at ‘p->stack_bottom’ would be partly retained,
> explaining the heap growth.
>
> I couldn’t pinpoint what exactly is keeping a pointer to the stack, but
> what I can tell is that the trick above makes that impossible (because
> we disable interior pointer tracing), hence the difference.
>
> Also, why changing the SCM_DYNSTACK_TYPE_DYNAMIC_STATE entry to an
> SCM_DYNSTACK_TYPE_UNWINDER entry would make a difference remains a
> mystery to me.
>
> I’m interested in theories that would explain all this in more detail!
> I’ll go ahead with the fix above if there are no objections.
I still am. :-)
Ludo’.
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