Path: csiph.com!x330-a1.tempe.blueboxinc.net!feeder3.hal-mli.net!nx02.iad01.newshosting.com!209.197.12.242.MISMATCH!nx01.iad01.newshosting.com!newshosting.com!news2.euro.net!feeder.news-service.com!85.214.198.2.MISMATCH!eternal-september.org!feeder.eternal-september.org!.POSTED!not-for-mail
From: Alexander Terekhov <terekhov@web.de>
Newsgroups: comp.programming.threads
Subject: Re: questions about memory_order_seq_cst fence
Date: Thu, 16 Jun 2011 12:03:23 +0200
Organization: A noiseless patient Spider
Lines: 30
Message-ID: <4DF9D4EB.81CDF399@web.de>
References: <43eb372b-6517-4914-b647-860f1f7136ba@k15g2000pri.googlegroups.com> <it5sht$i7j$1@node2.news.atman.pl> <b7657dae-d49f-4859-8020-b5d76bfae2cd@p9g2000prh.googlegroups.com> <itbb7k$uhh$1@node2.news.atman.pl>
Reply-To: terekhov@web.de
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Injection-Info: mx04.eternal-september.org; posting-host="MCbSEzW5qwGLFMNXJh39IQ"; logging-data="24206"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/2eMmfi4FrTAXFgqryIXt8s/ljkAlpCVg="
X-Mailer: Mozilla 4.77 [en] (Windows NT 5.0; U)
X-Accept-Language: en
Cancel-Lock: sha1:+4ZxgNNmU0uLfObkfw3p2FVtzG0=
Xref: x330-a1.tempe.blueboxinc.net comp.programming.threads:289


Edek wrote:
[...]
> As a side note, I compiled all ops on x86_64, and atomic<int>::load
> is mfence/load/mfence even for relaxed. I'd need some time to analyse
> the thing from perspective of other ops implementations in all
> orderings, and this leads me to the not so subtle question:
> 
> I understand people _should definitely_ use the default.
> I assume the goal, or the official word for it is 'rationale', was
> to let people 'who understand' write code that would be both portable
> and more efficient than the default. I am somehow beginning to doubt
> both my capabilities and whether this will be at all possible - I mean
> the efficiency, not portability (the latter can be simply done right).
> Though maybe the bottom line is that at least the precise implementation
> will have at least a couple of fences less than the default, at the
> price of - I think no one argues about that - complexity.

Try

http://www.decadent.org.uk/pipermail/cpp-threads/2008-December/001933.html
(Brief tentative example x86 Implementation for C/C++ Memory Model)

and

http://portal.acm.org/citation.cfm?id=1926394
(Mathematizing C++ concurrency)

regards,
alexander.