Date: Thu, 05 Jul 2001 16:28:40 -0600 From: "Justin T. Gibbs" <gibbs@scsiguy.com> To: John Baldwin <jhb@FreeBSD.org> Cc: Alfred Perlstein <bright@sneakerz.org>, Jake Burkholder <jake@FreeBSD.org>, cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org, Matt Dillon <dillon@earth.backplane.com>, Matthew Jacob <mjacob@feral.com>, Doug Rabson <dfr@nlsystems.com> Subject: Re: cvs commit: src/sys/sys systm.h condvar.h src/sys/kern kern_ Message-ID: <200107052228.f65MSeU64741@aslan.scsiguy.com> In-Reply-To: Your message of "Thu, 05 Jul 2001 12:37:47 PDT." <XFMail.010705123747.jhb@FreeBSD.org>
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>It happens with SMP, too, not just preemption. The calls are an optimization >to avoid problems with releasing the lock after the wakeup. The contention >can be avoided if we release the lock before calling wakeup(), but doing that >leaves a window open for another CPU to alter the data that the lock protects >possibly invalidating the wakeup that then gets sent. This window exists anyway. The locked mutex it not passed to the woken up thread, so there will always be a race between the woken up thread acquiring the mutex and some other thread on some other CPU acquiring it first and making the wakeup invalid. -- Justin To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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