Date: Thu, 22 Dec 2011 17:59:13 +0100 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: John Baldwin <jhb@freebsd.org> Cc: Poul-Henning Kamp <phk@phk.freebsd.dk>, freebsd-threads@freebsd.org, freebsd-arch@freebsd.org Subject: Re: [Patch] C1X threading support Message-ID: <86zkeksftq.fsf@ds4.des.no> In-Reply-To: <201112211028.26780.jhb@freebsd.org> (John Baldwin's message of "Wed, 21 Dec 2011 10:28:26 -0500") References: <73233.1324389741@critter.freebsd.dk> <86hb0ut1hq.fsf@ds4.des.no> <201112211028.26780.jhb@freebsd.org>
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John Baldwin <jhb@freebsd.org> writes: > Dag-Erling Sm=C3=B8rgrav <des@des.no> writes: > > Poul-Henning Kamp <phk@phk.freebsd.dk> writes: > > > mtx_unlock(l) > > > { > > > assert(l->id =3D=3D thread_id); > > > l->id =3D NULL; > > > atomic_magic_unlock(l->lock_field) > > > } > > susceptible to race conditions > How so? I should have specified "if called from a thread that does not own the mutex" > > > mtx_assert_held(l) > > > { > > > assert(l->lock-field !=3D 0); > > > assert(l->id =3D=3D thread_id); > > > } > > susceptible to race conditions > How so? I was going to point out that the state of the mutex can change between the two asserts, but as you say, at least one of them is guaranteed to fail... *if* you assume that these fields can be read atomically, which was one of my objections. DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no
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