[Mpi-22] Should all constants/types be available in all languagebindings?

[Supalov, Alexander]

Hi,

I think we should answer the following questions to decide whether and
how to define the constants:

1. When would a C MPI program call Fortran MPI subprogram? Probably,
never.
2. When would a Fortran MPI program call a C MPI subprogram? Sometimes.
3. When would a C++ MPI program call Fortran MPI program? Probably,
never.
4. When would a Fortran MPI program call a C++ MPI program? Probably,
never.

Here, "subprogram" means a part of program that relies on the MPI use or
knowledge of MPI datatypes, etc. This may or may not be a direct call
into the respective MPI library.

>From this, what is needed is to define Fortran datatypes from mpif.h in
C mpi.h. The rest does not seem relevant. Even the existing C++
definitions may just reflect C heritage.

Best regards.

Alexander

-----Original Message-----
From: mpi-22-bounces_at_[hidden]
[mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Jeff Squyres
Sent: Thursday, October 23, 2008 10:13 PM
To: MPI 2.2
Subject: [Mpi-22] Should all constants/types be available in all
languagebindings?

I notice that OMPI, MPICH2, Intel MPI, and HP MPI all do the following:

  * define Fortran datatypes in mpi.h (e.g., MPI_INTEGER, MPI_DOUBLE)
  * define Fortran datatypes in the C++ MPI namespace (e.g.,  
MPI::INTEGER, MPI::DOUBLE, etc.)
  * do *not* define C datatypes in mpif.h (e.g., MPI_INT, MPI_FLOAT,  
etc.)

Why?  AFAICT, there is no rule about what constants have to appear in  
which language bindings.  But doesn't that implicitly mean that all  
constants are supposed to appear in all language bindings?

(the argument for having MPI_DOUBLE available in C, for example, is  
that a C routine may be invoked to send or receive a message  
containing Fortran data.  Similar arguments exist for why you'd want  
MPI datatypes from other languages available in your language)

This is also related to whether the type MPI::Fint should exist or not.

I just filed a ticket about these issues
(https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/56 
) and marked it as "feedback requested", meaning that I need feedback  
from the Forum before a proposal can be made.

What do people think?


-- 
Jeff Squyres
Cisco Systems
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