[MPIWG Fortran] An implementation problem of F08 binding

[Junchao Zhang]

It came to my mind too. It should be easy for compilers to realize it is
the only specific procedure of the generic.
But it looks gcc does not do so.

--Junchao Zhang


On Thu, May 1, 2014 at 2:20 PM, William Gropp <wgropp at illinois.edu> wrote:

> The first problem is a quality of Fortran compiler implementation issue -
> there's no technical reason why the compiler can't tell you that "there is
> no subprogram MPI_SEND with a real for the second argument", for example.
>
> Bill
>
> William Gropp
> Director, Parallel Computing Institute
> Thomas M. Siebel Chair in Computer Science
> University of Illinois Urbana-Champaign
>
>
>
>
>
> On May 1, 2014, at 1:34 PM, Junchao Zhang wrote:
>
> Hello,
>    I met a problem when implementing F08 binding in MPICH.  I have a file
> mpi_f08.F90, which contains all interfaces
>
> module mpi_f08
> ..
> interface MPI_Send
>     subroutine MPI_Send_f08ts(buf, count, datatype, dest, tag, comm,
> ierror)
>         use :: mpi_f08_types, only : MPI_Datatype, MPI_Comm
>         implicit none
>         type(*), dimension(..), intent(in) :: buf
>         integer, intent(in) :: count, dest, tag
>         type(MPI_Datatype), intent(in) :: datatype
>         type(MPI_Comm), intent(in) :: comm
>         integer, optional, intent(out) :: ierror
>     end subroutine MPI_Send_f08ts
> end interface MPI_Send
> ..
> end module mpi_f08
>
> Then for each subroutine, I create a separate file which implement the
> wrapper function in Fortran.  For example, send_f08ts.F90 has
>
> subroutine MPI_Send_f08ts(buf, count, datatype, dest, tag, comm, ierror)
>     use :: mpi_f08, only : MPI_Datatype, MPI_Comm
>     use, intrinsic :: iso_c_binding, only : c_int
>     use :: mpi_c_interface, only : c_Datatype, c_Comm
>     use :: mpi_c_interface, only : MPIR_Send_cdesc
>
>     implicit none
>     ..
> end subroutine MPI_Send_f08ts
>
> Bill Long pointed out problems of the implementation. 1) When users supply
> a bad argument to MPI_Send(), the compiler complains "No specific match
> can be found for the generic subprogram call MPI_SEND", instead of
> pointing out the offending arg. 2) The wrapper is not in a module, which eliminates
> many of the advantages of using modern Fortran.
> I met the first problem in my testing. I was wondering if it is possible
> to fix that, so I ask Fortran expert here for advices.
> Thank you very much.
>
> --Junchao Zhang
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