From owner-freebsd-hackers@FreeBSD.ORG Fri Jan 13 10:20:50 2006 Return-Path: X-Original-To: freebsd-hackers@freebsd.org Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id A4DFE16A41F for ; Fri, 13 Jan 2006 10:20:50 +0000 (GMT) (envelope-from guomingyan@gmail.com) Received: from xproxy.gmail.com (xproxy.gmail.com [66.249.82.203]) by mx1.FreeBSD.org (Postfix) with ESMTP id 347CD43D48 for ; Fri, 13 Jan 2006 10:20:49 +0000 (GMT) (envelope-from guomingyan@gmail.com) Received: by xproxy.gmail.com with SMTP id t12so451481wxc for ; Fri, 13 Jan 2006 02:20:48 -0800 (PST) DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:references; b=Jx91Gov+Gv2MgpWkukhQyZWY3aWWFf8cOiFnSV2blyqKR6MMHD+S/4wNDTUCFed5UJOHcIOajLZmGQwj9RxJT6TYQZrcPx51hi5KDvoSfAXwapbpiIERbSzBrkCh/ZS5ZTY9Y08vE4N8DKEAZ/QEzV2c4X+Tz3+eR3yUTxND8jI= Received: by 10.70.52.9 with SMTP id z9mr2920564wxz; Fri, 13 Jan 2006 02:20:44 -0800 (PST) Received: by 10.70.39.18 with HTTP; Fri, 13 Jan 2006 02:20:43 -0800 (PST) Message-ID: <1fa17f810601130220h521590banff7d775a8bd4eaa6@mail.gmail.com> Date: Fri, 13 Jan 2006 18:20:43 +0800 From: prime To: "Kamal R. Prasad" In-Reply-To: MIME-Version: 1.0 References: <1fa17f810601122232l25551bc5n4e4a01ff6b7921e@mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: freebsd-hackers@freebsd.org Subject: Re: How priority propagation works on read/write lock? X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 13 Jan 2006 10:20:50 -0000 On 1/13/06, Kamal R. Prasad wrote: > > Priority need not be propagated to readers as they will not block other > readers. > Most likely, you only need to propagate to the writer to avoid priority > inversron. > > regards > -kamal > > > On 1/13/06, prime wrote: > > > Hi hackers, > > I have a question about how priority propagation works on > > read/write lock.On locks that have only one owner at a determinate > > moment,we can simply propagate the priority to the owner of lock,but > > read/write lock may have many owners at some time,so how can we know > > who are the owners? > > I browse the OpenSolaris' read/write lock implementation,and find > > that, it simply treats the owner of the lock as NULL when readers own > > the read/write lock.In this way,we can not propagate our priority to > > all threads that block us. > > > > Thanks very much. > > -- > > Three passions, simple but overwhelmingly strong, have governed my life= : > > > > the longing for love, the search for knowledge, and unbearable pity for > > the suffering of mankind. > > ---------Bertrand Russell > > _______________________________________________ > > freebsd-hackers@freebsd.org mailing list > > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.o= rg > > " > > > > Thanks your reply. But readers may block writers, aren't they? For example, there are three threads,A,B and C, and a read/write lock rwlock1 ,and a mutex mtx1. 1.A lock mtx1, 2.B get the read lock of rwlock1 and then want to get mtx1,but mtx1 is locked by A,so B has to wait on mtx1. 3.C want to get the write lock of rwlock1 and it has to wait,because rwlock1 is read locked by B. Now if C's priority < A's priority(in numerical), then we get priority inversion. How can avoid this priority inversion? Thanks. -- Three passions, simple but overwhelmingly strong, have governed my life: the longing for love, the search for knowledge, and unbearable pity for the suffering of mankind. ---------Bertrand Russell