Date: Sat, 22 Mar 2003 12:48:39 -0700 From: "Justin T. Gibbs" <gibbs@scsiguy.com> To: Poul-Henning Kamp <phk@phk.freebsd.dk>, Bakul Shah <bakul@bitblocks.com> Cc: arch@freebsd.org Subject: Re: memcpy() with specified direction of copying ? Message-ID: <8980000.1048362518@aslan.btc.adaptec.com> In-Reply-To: <9531.1047848405@critter.freebsd.dk> References: <9531.1047848405@critter.freebsd.dk>
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> Well, in my case it is a matter of shared memory where the order in > which I snapshot a data structure is critical for detecting integrity > issues. Without memory barriers, the order is undefined on many cpus irrespective of the direction of copy. So, for a data structure like this: start_tag some data ... end_tag A client knows that the data is stable if start_tag and end_tag are equal only if the data is written as: start_tag = new_tag; mb(); Fill the middle in whatever order is convenient; mb(); end_tag = new_tag; -- Justin To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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