[Mpi-forum] Big Fortran hole in MPI-4.0 Embiggening

[Rolf Rabenseifner]

Dear MPI-Forum members,

MPI-3.1 and MPI-4.0 includes the following rule on top of the 2nd page
of the Language Binding chapter:

| MPI implementations providing a Fortran interface must provide 
| one or both of the following:
| - The USE mpi_f08 Fortran support method.
| - The USE mpi and INCLUDE 'mpif.h' Fortran support methods.

The embiggening was included only in the C and mpi_f08 bindings.

Most implementors nowadays provide all three MPI Fortran support methods,
i.e., the mpi_f08 and the mpi module and mpif.h.

For all MPI-3.1 libraries that provide all three MPI Fortran support methods,
the most easiest and fastest way to provide MPI-4.0 for C and Fortran is,
 - to implement the embiggening for C,
 - and to remove the mpi_f08 module,
 - and maybe months or years later, to provide mpi_f08 again, now embiggened. 

This implementation path (by removing mpi_f08 from MPI-3.1 and to name 
it MPI-4.0 without Fortran embiggening) was of course never intended,
when we decided to require the embiggened routines only for mpi_f08.
The goal was 
 - to not require additional work from the implementors for the old mpi module
 - convince the users that it is a good idea to make a transition
   to mpi_f08.

The most simplest way to resolve this problem would be to require
mpi_f08 for MPI-4.0, i.e., to change the text to

| MPI implementations providing a Fortran interface 
| - must provide the USE mpi_f08 Fortran support method,
| - and additionally may provide both,
|   the USE mpi and INCLUDE 'mpif.h' Fortran support methods.

What is your opinion?

I expect that we should discuss this next Wednesday at our MPI Forum telcon.

Best regards
Rolf 

-- 
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) .