From owner-cvs-src@FreeBSD.ORG Tue Mar 13 15:32:43 2007 Return-Path: X-Original-To: cvs-src@freebsd.org Delivered-To: cvs-src@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 6CB7216A400; Tue, 13 Mar 2007 15:32:43 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from server.baldwin.cx (66-23-211-162.clients.speedfactory.net [66.23.211.162]) by mx1.freebsd.org (Postfix) with ESMTP id E5C0613C48C; Tue, 13 Mar 2007 15:32:42 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from localhost.corp.yahoo.com (john@localhost [127.0.0.1]) (authenticated bits=0) by server.baldwin.cx (8.13.8/8.13.8) with ESMTP id l2DFWbE6071321; Tue, 13 Mar 2007 10:32:37 -0500 (EST) (envelope-from jhb@freebsd.org) From: John Baldwin To: Julian Elischer Date: Tue, 13 Mar 2007 10:02:06 -0400 User-Agent: KMail/1.9.1 References: <200703092241.l29Mf2Ds062856@repoman.freebsd.org> <200703121618.41084.jhb@freebsd.org> <45F5E1F9.5090806@elischer.org> In-Reply-To: <45F5E1F9.5090806@elischer.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200703131002.07180.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH authentication, not delayed by milter-greylist-2.0.2 (server.baldwin.cx [127.0.0.1]); Tue, 13 Mar 2007 10:32:37 -0500 (EST) X-Virus-Scanned: ClamAV 0.88.3/2833/Tue Mar 13 08:55:31 2007 on server.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-4.4 required=4.2 tests=ALL_TRUSTED,BAYES_00 autolearn=ham version=3.1.3 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on server.baldwin.cx Cc: Attilio Rao , cvs-src@freebsd.org, src-committers@freebsd.org, Pawel Jakub Dawidek , cvs-all@freebsd.org Subject: Re: cvs commit: src/share/man/man9 Makefile condvar.9 lock.9 mi_switch.9 mtx_pool.9 mutex.9 rwlock.9 sleep.9 sleepqueue.9 sx.9 thread_exit.9 src/sys/kern kern_synch.c src/sys/sys mutex.h rwlock.h sleepqueue.h sx.h systm.h X-BeenThere: cvs-src@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: CVS commit messages for the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 13 Mar 2007 15:32:43 -0000 On Monday 12 March 2007 19:27, Julian Elischer wrote: > John Baldwin wrote: > > On Monday 12 March 2007 16:03, Pawel Jakub Dawidek wrote: > >> On Mon, Mar 12, 2007 at 03:35:21PM -0400, John Baldwin wrote: > >>> On Monday 12 March 2007 14:56, Pawel Jakub Dawidek wrote: > >>>> On Mon, Mar 12, 2007 at 11:16:23AM -0400, John Baldwin wrote: > >>>>> On Saturday 10 March 2007 15:52, Pawel Jakub Dawidek wrote: > >>>>>> What about something like this: > >>>>>> > >>>>>> #define cv_wait(cv, lock) do { > >>>>>> switch (LO_CLASSINDEX((struct lock_object *)(lock))) { > >>>>> The problem with a cast is you use type checking. Might as well do > > this: > >>>>> #define cv_wait(cv, lock) _cv_wait((cv), (struct lock_object *)(lock)) > >>>> This will skip type checking and my version only cast to provide type > >>>> checking, so when you pass some random variable it will give you an > >>>> error. > >>> Not really, you may pass some garbage and the LO_CLASSINDEX turns out to > > be a > >>> mutex. :) You only get a runtime error, not a compile-time one. > >>> Type-checking by the compiler is nice because you get compile-time errors. > >> I'll get compile-time error, because cv_wait_mtx() takes > >> 'struct condvar *' and 'struct mtx *' as arguments. So even if some > >> garbage returns 1, which turns out to be a mutex, call to cv_wait_mtx() > >> will generate compile-time error. > > > > Err, no, actually, yours will always give compile errors actually. Keep in > > mind that LO_CLASSINDEX() is a run-time check. This: > > > > #define cv_wait(cv, lock) do { > > switch (LO_CLASSINDEX((struct lock_object *)(lock))) { > > case 1: > > cv_wait_mtx(cv, lock); > > break; > > case 2: > > cv_wait_sx(cv, lock); > > break; > > case 3: > > cv_wait_rw(cv, lock); > > break; > > default: > > panic("Invalid lock."); > > } > > } while (0) > > > > Will try to pass 'lock' to three different functions, at least 2 of which will > > trigger compile errors. :) The kernel won't choose which one to run until > > runtime though. The key is that I want a compile error, not a panic(). :) > > I've been asking for awhile that for example spin and sleep mutexes should > be different types so that we could catch those problems at compile time. That is on my todo list actually. Stephan and I talked at BSDCan 06 about various alternative strategies for spin locks. -- John Baldwin