From owner-sc22wg5@open-std.org Sat Jan 24 12:59:09 2009 Return-Path: X-Original-To: sc22wg5-dom7 Delivered-To: sc22wg5-dom7@www2.open-std.org Received: by www2.open-std.org (Postfix, from userid 521) id 8F902CA3432; Sat, 24 Jan 2009 12:59:09 +0100 (CET) X-Original-To: sc22wg5@open-std.org Delivered-To: sc22wg5@open-std.org Received: from ppsw-1.csi.cam.ac.uk (ppsw-1.csi.cam.ac.uk [131.111.8.131]) by www2.open-std.org (Postfix) with ESMTP id EFDE8C56CFB for ; Sat, 24 Jan 2009 12:59:07 +0100 (CET) X-Cam-AntiVirus: no malware found X-Cam-SpamDetails: not scanned X-Cam-ScannerInfo: http://www.cam.ac.uk/cs/email/scanner/ Received: from hermes-2.csi.cam.ac.uk ([131.111.8.54]:59528) by ppsw-1.csi.cam.ac.uk (smtp.hermes.cam.ac.uk [131.111.8.151]:25) with esmtpa (EXTERNAL:nmm1) id 1LQhAH-0008M6-4L (Exim 4.70) (return-path ); Sat, 24 Jan 2009 11:59:05 +0000 Received: from prayer by hermes-2.csi.cam.ac.uk (hermes.cam.ac.uk) with local (PRAYER:nmm1) id 1LQhAH-0001mY-Ao (Exim 4.67) (return-path ); Sat, 24 Jan 2009 11:59:05 +0000 Received: from [83.67.89.123] by webmail.hermes.cam.ac.uk with HTTP (Prayer-1.3.1); 24 Jan 2009 11:59:05 +0000 Date: 24 Jan 2009 11:59:05 +0000 From: "N.M. Maclaren" To: MPI-3 Fortran working group , WG5 Subject: Re: [ukfortran] (SC22WG5.3920) [MPI3 Fortran] (j3.2006) (SC22WG5.3917) (SC22WG5.3909) [MPI3 Fortran] MPI non-blocking transfers Message-ID: In-Reply-To: <20090123233233.B4917CA5FED@www2.open-std.org> References: <49776DF7.1040900@cray.com> <20090121211748.130A5C178D9@www2.open-std.org> <20090121224014.6CB63C178D9@www2.open-std.org> <20090121234200.4F3BDCA3434@www2.open-std.org> <20090122000407.D5A8ECA3434@www2.open-std.org> <1232658808.15119.824.camel@math.jpl.nasa.gov> <20090123095622.CBD80CA5FED@www2.open-std.org> <20090123190515.A5B24CA5FE6@www2.open-std.org> <497A1CE5.3000708@cray.com> <20090123204209.615C8CA5FED@www2.open-std.org> <1232747203.15119.979.camel@math.jpl.nasa.gov> <497A51B9.3080304@cray.com> <20090123233233.B4917CA5FED@www2.open-std.org> X-Mailer: Prayer v1.3.1 Mime-Version: 1.0 Content-Type: text/plain; format=flowed; charset=ISO-8859-1 Sender: owner-sc22wg5@open-std.org Precedence: bulk On Jan 23 2009, Van Snyder wrote: > >> The copy-in/copy-out problem does not affect MPI_wait. There's no >> argument to copy anyway. Copy-in/copy-out is a serious problem for the >> earlier call to MPI_Isend, etc. where you do not want the copy temp >> being the buffer MPI sees, since it will get deleted when the call >> returns (which is before MPI is done with it.) This continues with any >> subsequent call to other routines that have the buffer as the argument, >> because a copy-out runs the risk of overwriting the buffer with the >> wrong values. > >The copy-in/copy-out problem appears to be pretty simple: Define the >buffer dummy argument of MPI_Isend to be ASYNCHRONOUS and assumed size. >Then if somebody hands it an assumed-shape or pointer buffer that's not >contiguous, the code falls afoul of C1239 or C1240. If the user's data >isn't contiguous, it's his responsibility to do the copying at the right >time. I agree. >I don't see the need for changes in the standard, either for the >copy-in/copy-out problem, or the code motion problem. Just define the >MPI interface properly. The only change that I think is necessary is some minor wording changes to extend the description to cover asynchronous I/O performed by a companion processor as well as Fortran asynchronous I/O. Technically, that's trivial. Regards, Nick Maclaren, University of Cambridge Computing Service, New Museums Site, Pembroke Street, Cambridge CB2 3QH, England. Email: nmm1@cam.ac.uk Tel.: +44 1223 334761 Fax: +44 1223 334679