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Date: Tue, 12 Dec 2000 22:01:42 -0600 (CST)
From: Jonathan Lemon <jlemon@flugsvamp.com>
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To: wollman@khavrinen.lcs.mit.edu, net@freebsd.org
Subject: Re: MEXT_IS_REF broken.
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In article <local.mail.freebsd-net/200012130250.VAA55319@khavrinen.lcs.mit.edu> you write:
><<On Tue, 12 Dec 2000 17:59:37 -0800, Alfred Perlstein
><bright@wintelcom.net> said:
>
>> Actually, in truth I think you can get the code right like so:
>
>> long x = _mmm->m_ext.ref_cnt->refcnt;
>> while (!atomic_cmpset_long(&_mmm->m_ext.ref_cnt->refcnt, x - 1, x))
>> 	;
>
>Cool!  You've just (almost) reinvented non-blocking parallel
>reference-counts.  Of course, what you really need is:
>
>long
>atomic_decrement_long(long *where)
>{
>	long oldval;
>
>	do {
>		oldval = *where;
>	} while (compare_exchange(where, &oldval, oldval - 1) != FAILURE);

Gee, this looks suspiciously like jhb's refcount patch:

	+static __inline int
	+refcount_release(refcount_t *count)
	+{
	+       int value;
	+
	+       do {
	+               value = *count - 1;
	+       } while (!atomic_cmpset_rel_int(count, value + 1, value));
	+       return (value == 0);
	+}

Sure you haven't been peeking at it?  :-) :-) :-)
--
Jonathan


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