[MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008 interface - issue with the LOGICAL kind

[Craig Rasmussen]

Bill Long, Jeff Squyres, and I had a phone conversation yesterday and came up with a straw man proposal.  We believe it fixes the LOGICAL argument problem while satisfying three major goals:

1. Backwards compatibility.
2. Flexibility so that efficient implementations can be produced on a variety of hardware.
3. Not dramatically increase the complexity for the tools community.
4. Ensure that the changes won't be seen by ordinary Fortran MPI users.

The straw man proposal is:

1. Remove the current binding names for MPI functions with LOGICAL dummy arguments (.  This must be done because these interfaces break the Fortran standard.
2. Replace the current binding names for MPI functions with LOGICAL dummy arguments with a different name and replacing LOGICAL type with default INTEGER arguments.  The name must be changed so as to not conflict with the current name with LOGICAL arguments.  For example, the binding name "MPI_Test_f08" will be replaced by "MPI_Test_int_f08" (exact replacement name open for discussion).  The Fortran implementation of the function MPI_Test must call MPI_Test_int_f08 as soon as possible for the tools implementers.
3. Implementation of the Fortran PMPI calling convention will be made optional (we think it already it).  If an MPI implementer doesn't provide the MPI_F08 binding names, then it must call the C MPI implementation in a thin Fortran wrapper so that the tools implementers can intercept the call in C.  An MPI implementation shall not provide/call both the MPI_F08 binding name and the C name.

Option 2 allows some MPI vendors to implement MPI functions entirely within Fortran (using the MPI_f08 binding names), if this is more efficient.

Option 3 allows some MPI implementations to place Fortran wrappers inside modules where they may be inlined by the compiler for efficiency.

Craig Rasmussen
CAS Scientific Programmer
rasmus at cas.uoregon.edu


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