[Mpi3-bwcompat] Stealing the working group

[Jeff Squyres]

On Jan 7, 2010, at 3:24 PM, Solt, David George wrote:

> Thanks for the suggestions.  I'm reworking the last proposals a bit.  My goal is to come up with something that allows for most interfaces (all but f77) to have a way to do large counts, leave f77 alone, and still have some consistency across languages and across what we already do.  
> 
> 1) Function overloading as available in Fortran90 and newer right?

I'd vote for the F2003 MPI bindings and later.  I don't really want to touch either the F77 or F90 bindings.

> 2) One concern I have with going to MPI_Count is that I think that MPI_Send(buf, 10, ....) should always be legal.   If we introduce a type that is up to the implementation, then that may not be legal any longer?  Do we specify in the standard that MPI_Count MUST be defined by the implementation to be something that can be cast to/from an integer constant?

Can you give an example where it won't be legal?

> 3) Another concern with introducing MPI_Count TYPE in Fortran90/newer is that it is inconsistent with the way other types are handled (MPI_Comm, MPI_Request, MPI_Info, etc.)   It seems a bit strange to me that we are going to pick out this one thing and make it a TYPE in all newer Fortrans even though everything else is declared as an INTEGER.

In the F2003 bindings, we have opaque types for all the MPI handles -- they're no longer integers.

:-)

That being said, there were some technical issues raised at the Portland meeting -- I can't remember many of them now, but one sticks out: what about functions that take a count as an OUT argument?  Those can't just seamlessly be recompiled (unless MPI_Count === int).


-- 
Jeff Squyres
jsquyres_at_[hidden]