Not only that, I think that there are some cases where tools *need* to intercept the Fortran call, not the C call. In OMPI, for example, we have a few corner cases where the Fortran MPI subroutine does *not* call the corresponding C MPI API function. Instead, it calls a back-end OMPI routine. One obvious case that jumps to mind is anything involving a callback. If you have integer handles in C, they might be able to get away with not swizzling/de-swizzling the arguments to the callback to the proper language. But this is not always the case. On Mar 20, 2013, at 12:29 PM, Hubert Ritzdorf <[email protected]> wrote:

Hi,

I think that Bill's proposal kills the Fortran Profiling Interface.

If the user defines a

subroutine MPI_Test (....)

do something

call PMPI _Test()

do something

end subroutine MPI_Test

then this function will never be executed because the Fortrran compiler may have already inlined the MPI_Test subroutine in the original code or the module version of MPI_Test is used.

Hubert ________________________________________ From: [email protected] [[email protected]] on behalf of Rolf Rabenseifner [[email protected]] Sent: Wednesday, March 20, 2013 6:09 PM To: [email protected]; MPI-3 Fortran working group Cc: Martin Schulz Subject: Re: [MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008 interface - issue with the LOGICAL kind

This mail contains a proposal how we can solve the current Fortran problems and possibly making the tools people also happy.

I need at least answers for - mpich (Bill Long), - OpenMPI (Jeff or Craig), - some tools people.

Let me summarize what I've learnt so far for mpi_f08:

- #364 about LOGICAL correction is a must. - MPI-3.0 allows BIND(C) and non-BIND(C), with the new restrictions in #364 - BIND(C) needs TR29113, therefore any implementation now should use non-BIND(C) for all non-TR29113 compilers. - Most (or all) try to use the non-BIND(C) interface. - Best way to do this are thin wrappers in Fortran that internally call - the oficial MPI-3.0 C binding (here, the tools people have a problem because they expect to wrap the Fortran interface and may therefore double-wrap), or - or an internal MPI-3.0 C routine (which is half-perfect for the tools folk, because they have to handle the implementation-dependant Fortran names with underscores). - And at least Bill wants to include the Fortran MPI library routines itselves in the mpi_f08 module. This is in conflict with the current MPI-3.0 linker naming rules.

Implications and proposal: - We should rewrite the linker names section MPI-3.0 17.1.5 with following goals: - Allow additionally to define that the PMPI is provided only on the MPI C interface and the Fortran MPI routines internally call the C interface; again, a macro definition in mpi.h tells whether this is chosen. Question: Would this cause a problem when linking a C or Fortran user application with some own MPI_Test etc. profiling routines that internally call PMPI_Test? - If Fortran profiling is done through the MPI C binding then there are no rules about the Fortran linker names needed, and therefore, one may put the thin Fortran wrappers into a Fortran module. - We can define BIND(C) for MPI routine groups as a future option that is currently not used. This would reduce the current effort for the tools people. Is there anybody who wants to implement one of the Fortran routine groups with BIND(C)?

I would expect, that this is the best to solve the problem that #364 prohibits BIND(C) for some routines and implementors want to do the same method for all routines.

Don't forget that BIND(C) and TR29113 is still important for implementing these thin wrappers internally.

Without using BIND(C) on the official mpi_f08 and mpi module interface, some features of TR29113 are not used: - the extension for interoperabple CHARACTER(LEN=*), - the extension for OPTIONAL dummy arguments.

Other TR29113 features are heavily used: - The DIMENSION(..), TYPE(*) is needed for some internal C-written MPI_Isend_desc. - The ASYNCHRONOUS usage for communication buffers.

Should we go in this direction?

Best regards Rolf

----- Original Message -----

...

From: "Bill Long" <[email protected]> To: "Jeff Squyres (jsquyres)" <[email protected]> Cc: "Martin Schulz" <[email protected]>, "MPI-3 Fortran working group" <[email protected]> Sent: Wednesday, March 20, 2013 4:01:52 PM Subject: Re: [MPI3 Fortran] [Mpi-comments] MPI 3.0: Fortran 2008 interface - issue with the LOGICAL kind On 3/20/13 8:26 AM, Jeff Squyres (jsquyres) wrote:

...

On Mar 20, 2013, at 6:25 AM, Bill Long <[email protected]> wrote:

...

interface !--> MPI_Test

! int MPI_Test(MPI_Request *request, int *flag, MPI_Status *status);

Function MPI_Test_C( request, flag, status) & BIND(C, name="MPI_Test") RESULT (res) import :: C_request, c_int, MPI_Status_C integer(C_request) :: request

This is not correct. You cannot assume that MPI handles are integers (they're pointers in Open MPI).

This is correct for mpich. OpenMPI would evidently have a different version. But the concept is still the same - make a correct interface to the C library routine, however it is defined by the implementation, and then call that from a thin Fortran wrapper that takes care of the issues related to LOGICAL, the use of default INTEGER, and OPTIONAL arguments.

Cheers, Bill

...

-- Bill Long [email protected] Fortran Technical Support & voice: 651-605-9024 Bioinformatics Software Development fax: 651-605-9142 Cray Inc./Cray Plaza, Suite 210/380 Jackson St./St. Paul, MN 55101

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