[Mpi-forum] [EXTERNAL] Re: An f2c question

[Pritchard Jr., Howard]

Hi Ralph,

Okay, not quite right, looks like both mpich and open mpi use %MPI_VAL, so I'll go with that.

Thanks,

Howard

On 8/24/21, 2:28 PM, "Rolf Rabenseifner" <rabenseifner at hlrs.de> wrote:

    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" <mpi-forum at lists.mpi-forum.org>
    > To: "Main MPI Forum mailing list" <mpi-forum at lists.mpi-forum.org>
    > Cc: "Pritchard" <howardp at lanl.gov>
    > 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
    > 
    > howardp at lanl.gov
    > 
    > 
    > 
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    > 
    > 
    > 
    > 
    > 
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    -- 
    Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de .
    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 .
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