From owner-freebsd-hackers Thu Dec 10 14:21:39 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id OAA28407 for freebsd-hackers-outgoing; Thu, 10 Dec 1998 14:21:39 -0800 (PST) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from alive.znep.com (sense-sea-MegaSub-1-222.oz.net [216.39.144.222]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id OAA28394 for ; Thu, 10 Dec 1998 14:21:36 -0800 (PST) (envelope-from marcs@znep.com) Received: from localhost (marcs@localhost) by alive.znep.com (8.9.1/8.9.1) with ESMTP id OAA12834; Thu, 10 Dec 1998 14:20:22 -0800 (PST) (envelope-from marcs@znep.com) Date: Thu, 10 Dec 1998 14:20:22 -0800 (PST) From: Marc Slemko To: "Richard Seaman, Jr." cc: "hackers@freebsd.org" Subject: Re: pread/pwrite In-Reply-To: <199812102156.PAA27450@ns.tar.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Thu, 10 Dec 1998, Richard Seaman, Jr. wrote: > I don't know if there is any interest in X/Open pread, pwrite > calls. Essentially, they implement atomic seek/write and > atomic seek/read calls. They are more useful in threaded > apps where you would need a file lock between a seek/write > or seek/read, but even in single threaded apps can allow > you to avoid a syscall. > > Attached is an implementation. If there is interest, and > if the implementation meets with approval, I'll submit > a PR. Or, perhaps someone would want to commit it directly. > > I welcome any comments. (not necessarily addressed specifically at pread/pwrite, but it does apply to it because of how it is used...) Where is the locking if multiple threads are reading and/or writing from or to the same descriptor at the same time? If you have x threads reading from a descriptor opened from a file on disk, do x-1 of them have to wait until the first one finishes before they can do anything? What about with mixed reading/writing? To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message