From owner-sc22wg5+sc22wg5-dom8=www.open-std.org@open-std.org Fri Apr 5 22:23:57 2013 Return-Path: X-Original-To: sc22wg5-dom8 Delivered-To: sc22wg5-dom8@www.open-std.org Received: by www.open-std.org (Postfix, from userid 521) id 418693565D7; Fri, 5 Apr 2013 22:23:51 +0200 (CEST) Delivered-To: sc22wg5@open-std.org Received: from exprod6og104.obsmtp.com (exprod6og104.obsmtp.com [64.18.1.187]) by www.open-std.org (Postfix) with ESMTP id A20963565D7 for ; Fri, 5 Apr 2013 22:23:43 +0200 (CEST) Received: from CFWEX01.americas.cray.com ([136.162.34.11]) (using TLSv1) by exprod6ob104.postini.com ([64.18.5.12]) with SMTP ID DSNKUV8yzZRAedfVrT5uSSGcXOuK4AqVPhJT@postini.com; Fri, 05 Apr 2013 13:23:47 PDT Received: from fortran.us.cray.com (172.31.19.200) by CFWEX01.americas.cray.com (172.30.88.25) with Microsoft SMTP Server id 14.2.342.3; Fri, 5 Apr 2013 15:16:31 -0500 Message-ID: <515F31A4.5060707@cray.com> Date: Fri, 5 Apr 2013 15:18:44 -0500 From: Bill Long Reply-To: Organization: Cray Inc. User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:17.0) Gecko/20130328 Thunderbird/17.0.5 MIME-Version: 1.0 To: sc22wg5 Subject: Re: (j3.2006) (SC22WG5.4964) [ukfortran] AW: Thoughts on Reinhold's thoughts References: <20130331013557.06C46356DD4@www.open-std.org> <20130401124437.69138356A01@www.open-std.org> <20130401140345.39966356D69@www.open-std.org> In-Reply-To: <20130401140345.39966356D69@www.open-std.org> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-sc22wg5@open-std.org Precedence: bulk On 4/1/13 9:03 AM, N.M. Maclaren wrote: > On Apr 1 2013, Bill Long wrote: >> >> Separate synchronizations of subteams is what SYNC TEAM does. If >> that's the model that best fits a particular program, then maybe the >> programmer should consider using SYNC TEAM instead of CHANGE TEAM. > > The use scenario being considered is the following: > > Most of the time, images run in the main team or without needing any > synchronisation. Every so often, SOME of them need to collaborate as > a subteam for a period, and then will rejoin the main team. The images > that are not part of the subteam are not involved in that collaboration > and have no obvious please to synchronise with it. This sounds like a good use of CHANGE TEAM with two subteams, SOME and REST. This guards against SOME starting to execute in its environment while the images in REST are still executing as part of the parent team. If that were not prevented, then 1) An image in REST (actually still in parent) could define or reference variables on an image in SOME -> havoc with the memory model. 2) The images of REST (actually still in parent) could execute SYNC ALL or allocate a coarray and hang until the images in SOME finish their subteam work and hit the END TEAM barrier. Meanwhile, images in SOME execute SYNC ALL or allocate coarrays without the REST images being aware. Seems ripe for more memory model havoc. If all of the images just stay in the parent team and selectively use SYNC TEAM for localized synchronization, you will have some confidence about the memory model (which in that context is unchanged from F08). Cheers, Bill > > Regards, > Nick Maclaren. > > _______________________________________________ > J3 mailing list > J3@mailman.j3-fortran.org > http://mailman.j3-fortran.org/mailman/listinfo/j3 > -- Bill Long longb@cray.com Fortran Technical Support & voice: 651-605-9024 Bioinformatics Software Development fax: 651-605-9142 Cray Inc./Cray Plaza, Suite 210/380 Jackson St./St. Paul, MN 55101