From: Jonas Hahnfeld via "Developers list for Guile, the GNU extensibility library" <guile-devel@gnu.org>
To: Maxime Devos <maximedevos@telenet.be>, guile-devel@gnu.org
Subject: Re: GC + Java finalization
Date: Sat, 03 Jul 2021 19:26:00 +0200 [thread overview]
Message-ID: <665d5bf795575a076321e7de74bef00023ae9355.camel@hahnjo.de> (raw)
In-Reply-To: <ebd60b072db9b040dbb393e0b5aca2aee106187c.camel@telenet.be>
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Am Samstag, dem 03.07.2021 um 19:14 +0200 schrieb Maxime Devos:
> Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library schreef op za 03-07-2021 om 14:05 [+0200]:
> > Hi Guile devs,
> >
>
> Hi, I'm not really a Guile dev but I'll respond anyway.
>
> > I'm hacking on GNU LilyPond and recently wondered if Guile could run
> > without Java finalization that prevents collection of chains of
> > unreachable objects.
>
> Do you have an example where this is a problem?
> I.e., did you encounter ‘chains of unreachable objects’ that were
> uncollectable, and so, where?
Sorry, I should have been clearer: Chains don't become uncollectable,
but a chain of N objects takes N collections to be completely reclaimed
(because Java finalization prepares for the possibility that a free
function makes an object live again, as Guile does for guardians). This
leads to unnecessary waste on the heap, and more work for the collector
(even though I haven't been able to measure so far).
>
> > I found that the functionality is only needed once
> > the first guardian is created, so it's possible to delay enabling the
> > mode until then. This required some fixes to free functions that
> > assumed dependent objects to be freed only later (see first two
> > patches).
> > The third patch delays ensuring Java finalization to scm_make_guardian,
> > but doesn't disable it explicitly (it's on by default in bdwgc). This
> > could now be done right after GC_INIT(), but it's not clear (at least
> > to me) whether client applications actually rely it, so I think it's
> > better if that's not done in Guile itself.
> >
> > Please consider applying, the fixes potentially also to stable-2.2.
> >
> > Thanks
> > Jonas
>
> I would need to look more closely at how ‘Java-style’ finalisation
> works. Some comments anyway:
>
> (first patch)
>
> > * test-suite/standalone/test-smob-mark.c
> > (init_smob_type): Correct size of smob type.
> > (free_x): Clear smob data instead of local variable.
> > (test_scm_smob_mark): Put smobs in array to ensure marking.
> >
> > - fprintf (stderr, "FAIL: SMOB mark function called for each SMOB\n");
> > + // Print pointer so it cannot be collected before.
> > + fprintf (stderr, "FAIL: SMOB mark function called for each SMOB (smobs = %p)\n", smobs);
> > exit (EXIT_FAILURE);
>
> Normally scm_remember_upto_here is used for that.
I think I tried, but it wasn't available. Or I mistyped, not sure.
> Also, I believe "/* */"-style comments are used customarily used in Guile
> instead of "//"-style comments.
>
> > static void
> > init_smob_type ()
> > {
> > - x_tag = scm_make_smob_type ("x", sizeof (x_t));
> > + x_tag = scm_make_smob_type ("x", sizeof (x_t *));
>
> This change seems to be a fix independent of the ‘do we want Java-style finalization’
> question.
Yes, that's why it's a separate patch.
>
> (third patch)
>
> Note that guardians are used in (ice-9 popen).
> They are also used by some guile libraries (e.g. guile-fibers),
> so you can't use (ice-9 popen) or any library using guardians
> if Java-style finalization is undesirable.
Yes, I'm aware and that's why any constructed guardian force-enables
Java finalization. But applications might not use it, and at least for
LilyPond I'm sure it's not used.
Jonas
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next prev parent reply other threads:[~2021-07-03 17:26 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-03 12:05 GC + Java finalization Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-07-03 17:14 ` Maxime Devos
2021-07-03 17:26 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library [this message]
2021-07-03 18:49 ` Maxime Devos
2021-07-03 18:54 ` Maxime Devos
2021-07-15 18:44 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-10-10 16:22 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-11-19 12:18 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2022-02-22 10:14 ` Dr. Arne Babenhauserheide
2022-02-22 15:12 ` Mike Gran
2021-11-19 13:13 ` Maxime Devos
2021-11-19 13:32 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-11-19 13:35 ` Maxime Devos
2021-11-19 13:40 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-11-19 13:44 ` Maxime Devos
2021-11-19 13:53 ` Maxime Devos
2021-11-19 13:53 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-11-19 14:01 ` Maxime Devos
2021-11-19 13:48 ` Maxime Devos
2021-11-19 13:55 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-11-19 14:14 ` Maxime Devos
2021-11-19 14:52 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-11-19 18:48 ` Maxime Devos
2021-11-19 19:01 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-11-19 13:15 ` Maxime Devos
2021-11-19 13:35 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-11-19 14:21 ` Maxime Devos
2021-11-19 15:32 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-11-19 13:17 ` Maxime Devos
2021-11-19 13:38 ` Jonas Hahnfeld via Developers list for Guile, the GNU extensibility library
2021-11-20 9:19 ` Maxime Devos
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