From owner-freebsd-hackers@FreeBSD.ORG  Fri Oct 10 00:46:03 2003
Return-Path: <owner-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 08EAD16A4B3
	for <freebsd-hackers@freebsd.org>;
	Fri, 10 Oct 2003 00:46:03 -0700 (PDT)
Received: from kientzle.com (h-66-166-149-50.SNVACAID.covad.net
	[66.166.149.50])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 65DE343FEC
	for <freebsd-hackers@freebsd.org>;
	Fri, 10 Oct 2003 00:45:56 -0700 (PDT)
	(envelope-from kientzle@acm.org)
Received: from acm.org ([66.166.149.54])
	by kientzle.com (8.12.9/8.12.9) with ESMTP id h9A7jlkX044947;
	Fri, 10 Oct 2003 00:45:47 -0700 (PDT)
	(envelope-from kientzle@acm.org)
Message-ID: <3F8663AA.4010707@acm.org>
Date: Fri, 10 Oct 2003 00:45:46 -0700
From: Tim Kientzle <kientzle@acm.org>
User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.4) Gecko/20031006
X-Accept-Language: en-us, en
MIME-Version: 1.0
To: Harti Brandt <brandt@fokus.fraunhofer.de>
References: <20031009194644.50B9116A4BF@hub.freebsd.org>
	<20031010091003.Q95881@beagle.fokus.fraunhofer.de>
In-Reply-To: <20031010091003.Q95881@beagle.fokus.fraunhofer.de>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
cc: freebsd-hackers@freebsd.org
Subject: Re: Dynamic reads without locking.
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
Reply-To: kientzle@acm.org
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 10 Oct 2003 07:46:03 -0000

Harti Brandt wrote:
> Yes. When I read the C standard
> 	foo = data & mask;
> wouldn't also help, because there is no sequence point in this statement
> except at the ;.

Before anyone takes this particular line of reasoning seriously,
I feel compelled to point out that sequence points have nothing to
do with this.

a) Sequence points are an "as if" requirement.  The
    program must produce the same results "as if" it
    strictly obeyed sequence points.  It doesn't have
    to really operate that way.  (And, in fact, well-optimized
    programs running on modern processors rarely do.)

b) Sequence points say NOTHING about how multiple
    threads or processors interact.

Sorry, but the C standard doesn't help here.  The
C standard does not address multi-threading at all.

Tim Kientzle