From owner-freebsd-arch@FreeBSD.ORG Sat Nov 24 16:25:45 2007 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 19CA616A420; Sat, 24 Nov 2007 16:25:45 +0000 (UTC) (envelope-from rwatson@FreeBSD.org) Received: from cyrus.watson.org (cyrus.watson.org [209.31.154.42]) by mx1.freebsd.org (Postfix) with ESMTP id E51DC13C458; Sat, 24 Nov 2007 16:25:44 +0000 (UTC) (envelope-from rwatson@FreeBSD.org) Received: from fledge.watson.org (fledge.watson.org [209.31.154.41]) by cyrus.watson.org (Postfix) with ESMTP id E027446CF9; Sat, 24 Nov 2007 11:28:45 -0500 (EST) Date: Sat, 24 Nov 2007 16:25:22 +0000 (GMT) From: Robert Watson X-X-Sender: robert@fledge.watson.org To: Attilio Rao In-Reply-To: <3bbf2fe10711240553k1eb35a5au23cae8af08f5864c@mail.gmail.com> Message-ID: <20071124162322.V14018@fledge.watson.org> References: <20071121222319.GX44563@elvis.mu.org> <3bbf2fe10711220753u435ff4cbxa94d5b682292b970@mail.gmail.com> <200711221726.27108.max@love2party.net> <20071123082339.GN44563@elvis.mu.org> <47469328.8020404@freebsd.org> <20071123092415.GP44563@elvis.mu.org> <4746F858.4070301@freebsd.org> <20071123235346.E14018@fledge.watson.org> <3bbf2fe10711231930m459dc800wbbb894b9fd50ca13@mail.gmail.com> <20071124103231.A14018@fledge.watson.org> <3bbf2fe10711240553k1eb35a5au23cae8af08f5864c@mail.gmail.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Stephan Uphoff , Max Laier , Alfred Perlstein , freebsd-arch@freebsd.org Subject: Re: rwlocks, correctness over speed. X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 24 Nov 2007 16:25:45 -0000 On Sat, 24 Nov 2007, Attilio Rao wrote: >> I must have missed recursion arriving then -- I'll modify uipc_usrreq.c to >> set the recursion flag on the rwlock in UNIX domain sockets rather than >> doing the nasty hack that was previously required. At the time, the hack >> was added because it seemed recursion was not going to be added to rwlocks, >> but sonewconn() behavior for listen sockets really ended up requiring it. > > attilio 2007-06-26 21:31:56 UTC > > FreeBSD src repository > > Modified files: > sys/kern kern_rwlock.c > sys/sys _rwlock.h rwlock.h > Log: > Introduce a new rwlocks initialization function: rw_init_flags. > This is very similar to sx_init_flags: it initializes the rwlock using > special flags passed as third argument (RW_DUPOK, RW_NOPROFILE, > RW_NOWITNESS, RW_QUIET, RW_RECURSE). > Among these, the most important new feature is probabilly that rwlocks > can be acquired recursively now (for both shared and exclusive paths). Yes, that was four months after I added rw_wowned(9) to work around the lack of recursion support. :-) However, it looks like the man page was never updated? It contains the following rather explicit language: Another important property is that shared holders of rwlock can recurse, but exclusive locks are not allowed to recurse. Robert N M Watson Computer Laboratory University of Cambridge