[MPI3 Fortran] What to do with mpif.h in MPI-3?

Torsten Hoefler htor at cs.indiana.edu
Sun Jan 24 17:38:52 CST 2010

> It seems that there is a spectrum of 4 options:
> 1. Deprecate mpif.h and MPI's implicit Fortran interfaces.  This is NOT removing mpif.h support from the spec or any implementation -- deprecating just states that the standard *MAY* remove them sometime in the future.  If we went this route, I'm sure that it would be a LOOOOONG time before mpif.h is removed from the spec because of the millions of lines of existing MPI codes out there that use it.
> 2. Don't deprecate mpif.h, but do not include any new MPI-3 functionality in it.  This is really only a minor distinction from deprecating; it's just a slightly less-strong statement meant to assure Fortran programmers that we are NOT abandoning mpif.h.  However, the road to all new MPI-3 functionality is via the proposed MPI-3 explicit bindings (i.e., "use mpi3").
> 3. Include all new MPI-3 functionality in mpif.h *except* for the "large count" functionality.  This allows mpif.h-using applications to get most of the MPI-3 goodness, with the exception that only INTEGER counts will be supported.  If your app needs larger counts than that, you must "use mpi3".
> 4. Include all new MPI-3 functionality in mpif.h, including "large count" functionality.
> What is everyone's opinion on which (1-4) the Forum should go with?
It seems like the route to go with the C-bindings (and also the general
bindings) is not clear yet and this would decide the outcome. Because if
we decide to take the "64-bit" (tm) approach and double the number of
function symbols, then the issue would be much simpler. However, if we
decide to take the int -> MPI_Count approach, then I don't see how we
can "extend" F77 in a standard-conforming and portable manner (but I
might miss something).

So depending on the outcome, I would vote:

- if we choose the extra function symbol for long types: option 4
- if we choose the MPI_Count approach: option 3

All the Best,

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Torsten Hoefler       | Postdoctoral Fellow
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