Date: Wed, 15 Nov 1995 12:08:47 -0500 From: "Garrett A. Wollman" <wollman@lcs.mit.edu> To: Poul-Henning Kamp <phk@critter.tfs.com> Cc: current@freebsd.org Subject: Re: cvs commit: src/sys/kern kern_sysctl.c Message-ID: <9511151708.AA26231@halloran-eldar.lcs.mit.edu> In-Reply-To: <3126.816454522@critter.tfs.com> References: <9511151641.AA26165@halloran-eldar.lcs.mit.edu> <3126.816454522@critter.tfs.com>
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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. -GAWollman -- Garrett A. Wollman | Shashish is simple, it's discreet, it's brief. ... wollman@lcs.mit.edu | Shashish is the bonding of hearts in spite of distance. Opinions not those of| It is a bond more powerful than absence. We like people MIT, LCS, ANA, or NSA| who like Shashish. - Claude McKenzie + Florent Vollant
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