Clearing stale references from the stack

Clearing stale references from the stack

[Ludovic Courtès]

Hi!

"Andy Wingo" <wingo@pobox.com> skribis:

> +;; Recurse through a C function that should clear any values that might
> +;; have spilled on the stack temporarily.  (The salient feature of
> +;; with-continuation-barrier is that currently it is implemented as a C
> +;; function that recursively calls the VM.)
> +;;
> +(define* (clear-stale-stack-references #:optional (n 10))
> +  (if (positive? n)
> +      (with-continuation-barrier
> +       (lambda ()
> +         (clear-stale-stack-references (1- n))))))
> +
>  ;;; Call THUNK with a given locale
>  (define (with-locale* nloc thunk)
>    (let ((loc #f))
> diff --git a/test-suite/tests/gc.test b/test-suite/tests/gc.test
> index 97eeb19..1afcea3 100644
> --- a/test-suite/tests/gc.test
> +++ b/test-suite/tests/gc.test
> @@ -49,13 +49,6 @@
>  ;;; 
>  ;;;
>  
> -(define (stack-cleanup depth)
> -  ;; Clean up stack space for DEPTH words.  This is defined here so that
> -  ;; `peval' doesn't inline it.
> -  (let cleanup ((i depth))
> -    (and (> i 0)
> -         (begin (cleanup (1- i)) i))))
> -

Note that ‘1-’ here is a subr call (because ‘stack-cleanup’ is
interpreted), so both procedures may have a similar effect, no?

Thanks,
Ludo’.

Re: Clearing stale references from the stack

[Andy Wingo]

Hello :-)

On Tue 31 Jan 2012 19:02, ludo@gnu.org (Ludovic Courtès) writes:

> "Andy Wingo" <wingo@pobox.com> skribis:
>
>> +;; Recurse through a C function that should clear any values that might
>> +;; have spilled on the stack temporarily.  (The salient feature of
>> +;; with-continuation-barrier is that currently it is implemented as a C
>> +;; function that recursively calls the VM.)
>> +;;
>> +(define* (clear-stale-stack-references #:optional (n 10))
>> +  (if (positive? n)
>> +      (with-continuation-barrier
>> +       (lambda ()
>> +         (clear-stale-stack-references (1- n))))))
>> +
>>  ;;; Call THUNK with a given locale
>>  (define (with-locale* nloc thunk)
>>    (let ((loc #f))
>> diff --git a/test-suite/tests/gc.test b/test-suite/tests/gc.test
>> index 97eeb19..1afcea3 100644
>> --- a/test-suite/tests/gc.test
>> +++ b/test-suite/tests/gc.test
>> @@ -49,13 +49,6 @@
>>  ;;; 
>>  ;;;
>>  
>> -(define (stack-cleanup depth)
>> -  ;; Clean up stack space for DEPTH words.  This is defined here so that
>> -  ;; `peval' doesn't inline it.
>> -  (let cleanup ((i depth))
>> -    (and (> i 0)
>> -         (begin (cleanup (1- i)) i))))
>> -
>
> Note that ‘1-’ here is a subr call (because ‘stack-cleanup’ is
> interpreted), so both procedures may have a similar effect, no?

I don't think so.  The question for me is, how far up the C stack does
this get?  For `stack-cleanup' (I have to learn how to type those nice
quotes some day), there will never be more than one `1-' frame active on
the C stack.  With clear-stale-stack-references, there will be `depth'
many.

I think!

Andy
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