Date: Thu, 16 Nov 1995 10:08:48 +0100 From: Poul-Henning Kamp <phk@critter.tfs.com> To: "Garrett A. Wollman" <wollman@lcs.mit.edu> Cc: current@freebsd.org Subject: Re: cvs commit: src/sys/kern kern_sysctl.c Message-ID: <4453.816512928@critter.tfs.com> In-Reply-To: Your message of "Wed, 15 Nov 1995 12:08:47 EST." <9511151708.AA26231@halloran-eldar.lcs.mit.edu>
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> <<On Wed, 15 Nov 1995 17:55:22 +0100, Poul-Henning Kamp <phk@critter.tfs.com> said: > > >> The purpose of this is to prevent race conditions even in a > >> uniprocessor system. > > > what race-conditions ? > > Say process 1 and process 2 are both trying to change some variable. > Process 1 gets the old value, but blocks before the new value is > changed. Process 2 then gets the old value, sets the new value, and > returns success. Process 1 then wakes up, and sets its new value, > thereby obliterating what process 2 had done, with neither process 1 > nor process 2 aware of what happened (unless they go back and check > again), because they will see the same `old' result. Ok, I guess that means we need it for that case at least... -- Poul-Henning Kamp | phk@FreeBSD.ORG FreeBSD Core-team. http://www.freebsd.org/~phk | phk@login.dknet.dk Private mailbox. whois: [PHK] | phk@ref.tfs.com TRW Financial Systems, Inc. Future will arrive by its own means, progress not so.
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