Dear Howard, SUBROUTINE MPI_TYPE_COMMIT(DATATYPE, IERR) INTEGER :: IERR ! some module USE to include the definition of TYPE(MPI_Datatype) TYPE(MPI_Datatype) :: DATATYPE CALL MPI_X_TYPE_COMMIT(DATATYPE%IMPI_VAL, IERR) RETURN END I do not know how to handle the optional ierr, but here is the way you should handle the datatype handle. Best regards Rolf ----- Original Message -----

From: "Main MPI Forum mailing list" <[email protected]> To: "Main MPI Forum mailing list" <[email protected]> Cc: "Pritchard" <[email protected]> Sent: Tuesday, August 24, 2021 10:19:27 PM Subject: [Mpi-forum] An f2c question

Hi All,

In porting an MPI application written mainly in Fortran and a little c to using mpi_f08 rather than mpi, I’ve hit an issue.

Namely, how would I write example 19.11 in the MPI 4 standard if the app uses type(MPI_Type) rather than integer?

Note I’m working with an application, so the MPI_Type structure is opaque, or at least I thought we’re supposed to treat it as opaque.

Here’s the example:

Example 19.11 The example below illustrates how the Fortran MPI function

MPI_TYPE_COMMIT can be implemented by wrapping the C MPI function

MPI_Type_commit with a C wrapper to do handle conversions. In this example a Fortran-C

interface is assumed where a Fortran function is all upper case when referred to from C and

arguments are passed by addresses.

! FORTRAN PROCEDURE

SUBROUTINE MPI_TYPE_COMMIT(DATATYPE, IERR)

INTEGER :: DATATYPE, IERR

CALL MPI_X_TYPE_COMMIT(DATATYPE, IERR)

RETURN

END

/* C wrapper */

void MPI_X_TYPE_COMMIT(MPI_Fint *f_handle, MPI_Fint *ierr)

{

MPI_Datatype datatype;

datatype = MPI_Type_f2c(*f_handle);

*ierr = (MPI_Fint)MPI_Type_commit(&datatype);

*f_handle = MPI_Type_c2f(datatype);

return;

}

Now I suspect that most of the time if one has some old ‘c’ code assuming a pointer to a 4 byte fortran integer argument for the datatype is just going to work, but I’d rather not just try to be lucky.

Anyway, there are fortran gurus on this project and they’d be sure to want a better solution.

Thanks for any help/ideas,

Howard

—

Howard Pritchard

Research Scientist

HPC-ENV

Los Alamos National Laboratory

[email protected]

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-- Dr. Rolf Rabenseifner . . . . . . . . . .. email [email protected] . 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) .