Re: GC + Java finalization

[Maxime Devos <maximedevos@telenet.be>]

Jonas Hahnfeld schreef op do 15-07-2021 om 20:44 [+0200]:
> From 33af6a98c6801e7b4880d1d3f78f7e2097c2174e Mon Sep 17 00:00:00
> 2001
> From: Jonas Hahnfeld <hahnjo@hahnjo.de>
> Date: Fri, 2 Jul 2021 23:03:17 +0200
> Subject: [PATCH 2/3] Avoid matching calls of scm_gc_free
> 
> There is no point in registering memory with the garbage collector
> if it doesn't need to do its job. In fact, calling scm_gc_free in
> a free function is wrong because it relies on Java finalization.
> 
> * libguile/random.c (scm_c_random_bignum): Replace matching calls of
>   scm_gc_calloc and scm_gc_free.
> * libguile/regex-posix.c (scm_make_regexp, regex_free): Avoid call
>   of scm_gc_free in free function.
> * test-suite/standalone/test-smob-mark.c (make_x, free_x): Avoid
>   call of scm_gc_free in free function.
> ---
>  THANKS                                 | 1 +
>  libguile/random.c                      | 8 ++------
>  libguile/regex-posix.c                 | 6 +++---
>  test-suite/standalone/test-smob-mark.c | 4 ++--
>  4 files changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/THANKS b/THANKS
> index aa4877e95..786b65d1a 100644
> --- a/THANKS
> +++ b/THANKS
> @@ -13,6 +13,7 @@ Contributors since the last release:
>           Volker Grabsch
>           Julian Graham
>          Michael Gran
> +          Jonas Hahnfeld
>           Daniel Hartwig
>               No Itisnt
>             Neil Jerram
> diff --git a/libguile/random.c b/libguile/random.c
> index 63da7f5d6..ac400a9fd 100644
> --- a/libguile/random.c
> +++ b/libguile/random.c
> @@ -324,9 +324,7 @@ scm_c_random_bignum (scm_t_rstate *state, SCM m)
>    /* we know the result will be this big */
>    mpz_realloc2 (SCM_I_BIG_MPZ (result), m_bits);
>  
> -  random_chunks =
> -    (uint32_t *) scm_gc_calloc (num_chunks * sizeof (uint32_t),
> -                                     "random bignum chunks");
> +  random_chunks = (uint32_t *) scm_calloc (num_chunks * sizeof
> (uint32_t));
>  
>    do
>      {
> @@ -363,9 +361,7 @@ scm_c_random_bignum (scm_t_rstate *state, SCM m)
>        /* if result >= m, regenerate it (it is important to
> regenerate
>  	 all bits in order not to get a distorted distribution) */
>      } while (mpz_cmp (SCM_I_BIG_MPZ (result), SCM_I_BIG_MPZ (m)) >=
> 0);
> -  scm_gc_free (random_chunks,
> -               num_chunks * sizeof (uint32_t),
> -               "random bignum chunks");
> +  free (random_chunks);

From the manual (about scm_gc_calloc & friends):

‘Memory blocks allocated this way may
be released explicitly; however, this is not strictly needed, and we
recommend _not_ calling ‘scm_gc_free’.  All memory allocated with
‘scm_gc_malloc’ or ‘scm_gc_malloc_pointerless’ is automatically
reclaimed when the garbage collector no longer sees any live reference
to it(1).’

As such, I'd recommend simply dropping the scm_gc_free
(here and in other places), if the scm_gc_free was problematic
because of Java finalization reasons.


>    return scm_i_normbig (result);
>  }
>  
> diff --git a/libguile/regex-posix.c b/libguile/regex-posix.c
> index a08da02db..36bb639e0 100644
> --- a/libguile/regex-posix.c
> +++ b/libguile/regex-posix.c
> @@ -67,7 +67,7 @@ static size_t
>  regex_free (SCM obj)
>  {
>    regfree (SCM_RGX (obj));
> -  scm_gc_free (SCM_RGX (obj), sizeof(regex_t), "regex");
> +  free (SCM_RGX (obj));
>    return 0;
>  }
>  
> @@ -164,7 +164,7 @@ SCM_DEFINE (scm_make_regexp, "make-regexp", 1, 0,
> 1,
>        flag = SCM_CDR (flag);
>      }
>  
> -  rx = scm_gc_malloc_pointerless (sizeof (regex_t), "regex");
> +  rx = scm_malloc (sizeof (regex_t));

If the regex why scm_gc_malloc_pointerless -> scm_malloc?
Is rx not pointerless? You coud simply ...


> -      scm_gc_free (rx, sizeof(regex_t), "regex");
> +      free (rx);

drop the scm_gc_free AFAIK.

Greetings,
Maxime