[mpiwg-rma] [MPIWG Fortran] "small count" variants of RMA functions

[Jeff Hammond]

I created https://github.com/mpi-forum/mpi-issues/issues/528.

Normally, we would have a Fortran WG meeting during the quarterly meeting.
Is there going to be a Fortran WG session at the December meeting?

Jeff

On Sat, Nov 27, 2021 at 9:14 PM William Gropp <wgropp at illinois.edu> wrote:

> I agree with Jeff here.  This is a good enhancement; I believe the only
> reason that we hadn’t done this before is that we’ve stuck closely to the
> original Fortran look-and-feel - which was pre-Fortran 90.  We could have
> done this earlier, and now that there are explicit interfaces that are only
> available in Fortran08, there is no reason not to do this.
>
> Bill
>
> William Gropp
> Director, NCSA
> Thomas M. Siebel Chair in Computer Science
> University of Illinois Urbana-Champaign
> IEEE-CS President-Elect
>
>
>
>
> On Nov 25, 2021, at 4:42 AM, Jeff Hammond via mpiwg-fortran <
> mpiwg-fortran at lists.mpi-forum.org> wrote:
>
> RMA absolutely did the right thing with MPI_Aint size and displacement
> arguments.
>
> In C, it is no problem to pass 32b integers to these arguments when AINT
> is 64b, because C type promotion rules just work.
>
> In Fortran, I cannot do this, because an integer literal is not compatible
> with an AINT argument.  I find it tedious to have to declare a variable
> just for this, or to explicitly cast with integer(100,MPI_ADDRESS_KIND).
>
> Since Fortran does polymorphism right and can have subroutine declarations
> for both default integer and AINT integer scalar arguments, is there a good
> reason not to add the former?
>
> This proposal applies not to just MPI_Win_allocate but any RMA function
> that uses AINT scalar arguments.
>
> Thanks,
>
> Jeff
>
> % mpifort y.F90
> y.F90:20:60:
>
>    20 |   call MPI_Win_allocate(100, 1, MPI_INFO_NULL, comm, XA, WA)
>       |                                                            1
> Error: There is no specific subroutine for the generic 'mpi_win_allocate'
> at (1)
>
> % cat y.F90
> ! USE mpi_f08
> ! MPI_Win_allocate(size, disp_unit, info, comm, baseptr, win, ierror)
> !    USE, INTRINSIC :: ISO_C_BINDING, ONLY : C_PTR
> !    INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: size
> !    INTEGER, INTENT(IN) :: disp_unit
> !    TYPE(MPI_Info), INTENT(IN) :: info
> !    TYPE(MPI_Comm), INTENT(IN) :: comm
> !    TYPE(C_PTR), INTENT(OUT) :: baseptr
> !    TYPE(MPI_Win), INTENT(OUT) :: win
> !    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
> program main
>   use iso_fortran_env
>   use mpi_f08
>   implicit none
>   integer(kind=MPI_ADDRESS_KIND) :: as = 100
>   type(c_ptr) :: XA
>   type(MPI_Win) :: WA
>   TYPE(MPI_Comm) :: comm = MPI_COMM_WORLD
>   call MPI_Win_allocate(as, 1, MPI_INFO_NULL, comm, XA, WA)
>   call MPI_Win_allocate(100, 1, MPI_INFO_NULL, comm, XA, WA)
> end program main
>
> % mpicc y.c && echo SUCCESS
> SUCCESS
>
> % cat y.c
> #include <mpi.h>
> int main(void)
> {
>   MPI_Aint as = 100;
>   int * XA;
>   MPI_Win WA;
>   MPI_Win_allocate(as, 1, MPI_INFO_NULL, MPI_COMM_WORLD, XA, &WA);
>   MPI_Win_allocate(100, 1, MPI_INFO_NULL, MPI_COMM_WORLD, XA, &WA);
> }
>
>
> --
> Jeff Hammond
> jeff.science at gmail.com
> http://jeffhammond.github.io/
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>
>

-- 
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/
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