Date: Wed, 27 Mar 2002 12:10:36 -0800 (PST) From: Julian Elischer <julian@elischer.org> To: arch@freebsd.org Cc: smp@freeBSD.org Subject: SMP safe reference counting Message-ID: <Pine.BSF.4.21.0203271150430.47944-100000@InterJet.elischer.org>
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[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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