Date: Thu, 16 Sep 2004 21:52:41 -0400 From: John Baldwin <jhb@FreeBSD.org> To: "M. Warner Losh" <imp@bsdimp.com> Cc: nate@root.org Subject: Re: cvs commit: src/sys/dev/md md.c Message-ID: <200409162152.41670.jhb@FreeBSD.org> In-Reply-To: <20040916.185915.35504747.imp@bsdimp.com> References: <20040916204321.GE30151@darkness.comp.waw.pl> <414A109E.4080601@samsco.org> <20040916.185915.35504747.imp@bsdimp.com>
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On Thursday 16 September 2004 08:59 pm, M. Warner Losh wrote: > In message: <414A109E.4080601@samsco.org> > > Scott Long <scottl@samsco.org> writes: > : Or just use a semaphore. > > Or a condition variable. That doesn't help, a condition variable doesn't have state like a semaphore. The correct fix is to do this: thread A ---------- mtx_lock(); adjust_state(); mtx_unlock(); wakeup(); thread B --------- mtx_lock(); while (state_still_needs_sleep()) msleep(...) mtx_unlock() Proving that there is no race is left as an exercise to the reader. :) -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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