From owner-freebsd-hackers Fri May 12 15:39:11 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from fw.wintelcom.net (ns1.wintelcom.net [209.1.153.20]) by hub.freebsd.org (Postfix) with ESMTP id 4C42237BBC1 for ; Fri, 12 May 2000 15:39:09 -0700 (PDT) (envelope-from bright@fw.wintelcom.net) Received: (from bright@localhost) by fw.wintelcom.net (8.10.0/8.10.0) id e4CNB7E21528; Fri, 12 May 2000 16:11:07 -0700 (PDT) Date: Fri, 12 May 2000 16:11:07 -0700 From: Alfred Perlstein To: Sergey Babkin Cc: Ville-Pertti Keinonen , FengYue , hackers@FreeBSD.ORG Subject: Re: Why this works? Message-ID: <20000512161107.A19644@fw.wintelcom.net> References: <20000511210915.A38341@Hamilton-ppp44812.sympatico.ca> <864s84cq35.fsf@not.demophon.com> <20000512005806.A29302@fw.wintelcom.net> <391C7CDA.F9B477B7@bellatlantic.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0.1i In-Reply-To: <391C7CDA.F9B477B7@bellatlantic.net>; from babkin@bellatlantic.net on Fri, May 12, 2000 at 05:51:22PM -0400 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG * Sergey Babkin [000512 15:23] wrote: > Alfred Perlstein wrote: > > > > * Ville-Pertti Keinonen [000511 22:49] wrote: > > > > > > fengyue@bluerose.windmoon.nu (FengYue) writes: > > > > > > > loop. Now, the third program reads 4K of data from /tmp/pagetest > > > > and exit if the 4K data does not contain all 'A's nor 'Z's. 3 programs > > > > run concurrently on the same machine (3.4). No lock in the code whatsoever, > > > > > > Not quite. If FreeBSD didn't perform locking, operations affecting > > > single filesystem blocks would probably be atomic (as long as the > > > userland buffer is in memory). > > > > > > However, FreeBSD does perform locking in read(2) and write(2) for > > > local files, so your third program should never fail and exit. > > > > > > Note that the system call interface does not guarantee reads or writes > > > to be atomic, this just happens to be how it is implemented at the > > > moment. > > > > Afaik several Unix standards mandate this behavior, Linux doesn't > > follow this standard though. > > Sounds like one more of these subtle weirdnesses in Linux that > annoy me so much :-( This weirdness is intentional, it's a shortcut for speed taken at the expense of real unix compatibility. > Solaris seems to be another example a system with not quite atomic > writes. The writes themselves seem to be atomic but in append mode the > positioning at the end of file is not atomic with writes. So when > appending to a log file from multiple sources the messages tend to > overlap (be written at the same position). That's why I use FreeBSD, it works. :) -- -Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org] "I have the heart of a child; I keep it in a jar on my desk." To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message