Date: Tue, 20 Dec 2011 14:02:21 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-threads@freebsd.org, Niall Douglas <s_sourceforge@nedprod.com>, freebsd-arch@freebsd.org Subject: Re: [Patch] C1X threading support Message-ID: <73233.1324389741@critter.freebsd.dk> In-Reply-To: Your message of "Tue, 20 Dec 2011 08:22:25 EST." <201112200822.26369.jhb@freebsd.org>
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In message <201112200822.26369.jhb@freebsd.org>, John Baldwin writes:
>The reason I can think of why you might not specify
>this is if you want to support machines that have very limited support for
>atomic operations (e.g. only an exchange instruction or a single-bit test-and-
>set as opposed to a full-world test-and-set such as cmpxchg on x86 or cas on
>sparc).
There is no way this can be impossible on a platform which can
implement a mutex in the first place:
mtx_lock(l)
{
atomic_magic_lock(l->lock_field)
l->id = thread_id;
}
mtx_unlock(l)
{
assert(l->id == thread_id);
l->id = NULL;
atomic_magic_unlock(l->lock_field)
}
mtx_assert_held(l)
{
assert(l->lock-field != 0);
assert(l->id == thread_id);
}
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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