[MPI3 Fortran] Proposing changes to Fortran 2008

[Supalov, Alexander]

PPS. John apparently retired from the Rutherford Labs but remained
active. Please pass my best wishes to him next time you meet. 

-----Original Message-----
From: mpi3-fortran-bounces at lists.mpi-forum.org
[mailto:mpi3-fortran-bounces at lists.mpi-forum.org] On Behalf Of
Aleksandar Donev
Sent: Thursday, March 27, 2008 9:31 PM
To: MPI-3 Fortran working group
Subject: Re: [MPI3 Fortran] Proposing changes to Fortran 2008

Hi,

MPI_ISend has many more issues than MPI_Send. Which one are we
discussing?

For MPI_Send, I see no problem with copy in/out, in fact, I see it as 
desirable because the compiler does the work of copying things like
columns 
of arrays into contig buffers. Is there a problem with copy in/out and
the 
blocking calls?

> The C_LOC functionality is not far away from this requirement
C_LOC exactly satisfies the requirement of no copy in/out and probably
should 
be used for MPI_ISend. It requires TARGET, which should in fact be
required 
if you are retaining a pointer to an array (even if this pointer is only
in C 
and not visible to the Fortran compiler).

> the ASYNCHRONOUS attribute also avoids any copying of the actual
argument.
In the case of MPI_ISend even with C_LOC, ASYNCHRONOUS (actually
VOLATILE, to 
be exact) is necessary on the array whose values are being modified
behind 
the compiler's back. This is independent of the issue of copying.

Best,
Aleks

P.S. John Reid is still the head of the Fortran committee

-- 
Aleksandar Donev, Ph.D.
Lawrence Postdoctoral Fellow @ Lawrence Livermore National Laboratory
High Performance Computational Materials Science and Chemistry
E-mail: donev1 at llnl.gov
Phone: (925) 424-6816  Fax: (925) 423-0785
Address: P.O.Box 808, L-367, Livermore, CA 94551-9900
Web: http://cherrypit.princeton.edu/donev
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