[MPIWG Fortran] Provide Fortran datatypes if Fortran bindings not provided?

[Jeff Hammond]

On Thu, Feb 18, 2016 at 1:43 PM, Rolf Rabenseifner <rabenseifner at hlrs.de>
wrote:

> > I think you have (1) and (2) backwards in this paragraph.
> Yes, I did it with the wrong numbers. I corrected it below.
>
> > I think JeffH and Jed want (1).
> > I think I want (1), too.
>
> I see the point.
> I have not a strong opinion and would like to know,
> what the other representatives in the Forum would like to see,
> because
>
> (2) MPI_DATATYPE_NULL is what they mainly have today.
> (1) "not existing" would be a real change.
>
>
Real only in the sense that things will break at compile-time instead of
run-time.  We are not breaking any working programs if we make this change.

Jeff


> Rolf
>
> ----- Original Message -----
> > From: "Jeff Squyres" <jsquyres at cisco.com>
> > To: "MPI-WG Fortran working group" <mpiwg-fortran at lists.mpi-forum.org>
> > Sent: Thursday, February 18, 2016 10:31:23 PM
> > Subject: Re: [MPIWG Fortran] Provide Fortran datatypes if Fortran
>  bindings        not provided?
>
> > On Feb 18, 2016, at 3:55 PM, Rolf Rabenseifner <rabenseifner at hlrs.de>
> wrote:
> >>
> >> I would prefer a solution where an application or middlware can check at
> >> runtime whether the Fortran MPI datatypes exist, i.e., I like mpich's
> >> solution. It is more simple than all methods that People must check
> prior
> >> to compile and must remove or Change parts of there software.
> >
> > The reason that JeffH and Jed hate this solution is because it makes it
> quite
> > difficult for an application to know whether the MPI has Fortran support
> or not
> > -- they basically have to compile an MPI application *and then run it*
> to see
> > if the datatypes are actually MPI_DATATYPE_NULL.
> >
> > Doing this inside a GNU Autoconf/configure script is very, very difficult
> > because of the huge differences in how you launch MPI applications across
> > different HPC environments.
> >
> > Their (strong) preference is that you can have a simple compilation test
> in the
> > GNU Autoconf/configure script that just tries to compile something like
> the
> > following:
> >
> > -----
> > #include <mpi.h>
> > MPI_Datatype foo = MPI_INTEGER;
> > -----
> >
> > If that compiles, then your MPI has Fortran support.
> > If it doesn't compile, your MPI doesn't have Fortran support.
> >
> >> In the moment,in the case of a missing accompanying Fortran Compiler,
> >> an application or middleware that wants to handle
> >> MPI Fortran datatypes must handle both cases
> >> (1) mpi.h does not provide a specific MPI Fortran datatype
> >> (2) mpi.h provides this MPI Fortran datatype as MPI_DATATYPE_NULL
> >>
> >> The additional case, that it is mapped to a real datatype is not
> >> an exception, because it defines some sort of accompanying Fortran
> Compiler.
> >>
> >> I would prefer that the MPI standard defines, which of the two
> >> options should be implemented.
> >
> > I think JeffH and Jed want (1).
> >
> > I think I want (1), too.
> >
>    As said at the beginning, I would prefer (2),
> >> - as mpich is doing it in general, and
> >> - OMPI is doing it partially,
>    whereas (1) was not done by mpich nor by OMPI.
> >
> >
> > --
> > Jeff Squyres
> > jsquyres at cisco.com
> > For corporate legal information go to:
> > http://www.cisco.com/web/about/doing_business/legal/cri/
> >
> > _______________________________________________
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> > mpiwg-fortran at lists.mpi-forum.org
> > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-fortran
>
> --
> Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
> High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
> University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
> Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
> Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307)
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>



-- 
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/
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