Date: Tue, 12 Dec 2000 22:01:42 -0600 (CST) From: Jonathan Lemon <jlemon@flugsvamp.com> To: wollman@khavrinen.lcs.mit.edu, net@freebsd.org Subject: Re: MEXT_IS_REF broken. Message-ID: <200012130401.eBD41gc95284@prism.flugsvamp.com> In-Reply-To: <local.mail.freebsd-net/200012130250.VAA55319@khavrinen.lcs.mit.edu> References: <local.mail.freebsd-net/20001211014837.W16205@fw.wintelcom.net> <local.mail.freebsd-net/Pine.BSF.4.21.0012111223350.21769-100000@jehovah.technokratis.com> <local.mail.freebsd-net/20001212014429.Y16205@fw.wintelcom.net> <local.mail.freebsd-net/20001212015059.Z16205@fw.wintelcom.net> <local.mail.freebsd-net/20001212143214.H2312@canonware.com> <local.mail.freebsd-net/20001212175937.M16205@fw.wintelcom.net>
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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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