Date: Thu, 28 Mar 2002 00:02:40 -0500 From: Bosko Milekic <bmilekic@unixdaemons.com> To: Julian Elischer <julian@elischer.org> Cc: arch@FreeBSD.ORG Subject: Re: SMP safe reference counting Message-ID: <20020328000240.A94897@unixdaemons.com> In-Reply-To: <Pine.BSF.4.21.0203271150430.47944-100000@InterJet.elischer.org>; from julian@elischer.org on Wed, Mar 27, 2002 at 12:10:36PM -0800 References: <Pine.BSF.4.21.0203271150430.47944-100000@InterJet.elischer.org>
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I don't think we really need a ref. count API, per-se. I can think of
several places that may need to do ref. counting but wouldn't want to
do it with a bus-locked instruction because their reference counter(s)
are already protected by an existing mutex.
-Bosko
On Wed, Mar 27, 2002 at 12:10:36PM -0800, Julian Elischer wrote:
>
> [please remove -smp from your reply]
>
> Once again on the SMP list a lock is being used to make a reference count
> safe. I'd like to re-raise the issue of a safe reference counting
> fascility.
>
> what would be the semantics?
>
> typedef volatile u_int ref_cnt;
> typedef void ref_free(void *);
>
> reference_add(ref_cnt *);
> reference_drop(ref_cnt *, ref_free *, void *);
>
>
>
>
>
> __inline void
> reference_add(ref_cnt *cnt) {
> atomic_inc(cnt);
> }
>
> /* Note I use the non-existing "atomic_inc()". I think
> we should have this as its SO COMMONLY used. */
>
> __inline void
> reference_drop(ref_cnt *cnt, ref_free *fn. void * arg) {
> int newcount;
> int oldcount;
>
> do {
> newcount = (oldcount = *cnt) - 1;
> } while (atomic_cmp_and_set(cnt, oldcount, newcount) == ACS_FAILED);
> }
> /* I can't remember off the top of my head the cmp-and-set command */
>
>
>
>
>
>
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>
--
Bosko Milekic
bmilekic@unixdaemons.com
bmilekic@FreeBSD.org
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