Date: Tue, 4 Dec 2007 08:58:53 +0000 (GMT) From: Jan Grant <jan.grant@bristol.ac.uk> To: Alfred Perlstein <alfred@freebsd.org> Cc: Karsten Behrmann <BearPerson@gmx.net>, freebsd-arch@freebsd.org Subject: Re: Code review request: small optimization to localtime.c Message-ID: <20071204085502.N83722@tribble.ilrt.bris.ac.uk> In-Reply-To: <20071204014614.GE76623@elvis.mu.org> References: <20071128.151021.709401576.imp@bsdimp.com> <20071203235929.685d3674@Karsten.Behrmanns.Kasten> <20071204014614.GE76623@elvis.mu.org>
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On Mon, 3 Dec 2007, Alfred Perlstein wrote: [on the double-checked locking idiom] > Karsten, _typically_ (but not always) an "unlock" operation > requires that writes prior to the unlock be globally visible. > > This is why it works almost everywhere. Perhaps, but if you use it you should probably mark the code with /* XXX not guaranteed to be correct by POSIX */ Double-checked locking is broken without an appropriate barrier. "Correctness over speed" should surely be our watchword :-) Cheers, jan -- jan grant, ISYS, University of Bristol. http://www.bris.ac.uk/ Tel +44 (0)117 3317661 http://ioctl.org/jan/ Hang on, wasn't he holding a wooden parrot? No! It was a porcelain owl.
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