[MPI3 Fortran] (j3.2006) (SC22WG5.3823) Please tell me I'm wrong

[Craig E. Rasmussen]

Jim,

Thanks for your response.  The question was not really how to get around
the problem but to ask why the problem exists in the first place.  MPI
users have been using generic MPI interfaces for years (using F77 style
implicit interfaces) so they won't be happy if they have to change their
codes in this way.

I think I have figured out the reasoning.  I can argument associate a 2D
array with a 1D dummy specified as

    real :: dimension(*) :: dummy_array

However, generic resolution can't be used to resolve a procedure calling
with a 2D actual to a 1D dummy.

Is this reasoning correct?

Thanks,
Craig



> Craig
>
> If your message is a contiguous assumed-shape, then you can solve the
> problem without Fortran committee's help by using a conversion function as
> follows
>
> function convertToRank1 (x, n) result (res)
>    real, target, intent(inout) :: x(n)
>    integer, intent(in) :: n
>
>    real, pointer :: res(:)
>
>    res => x
> end function
>
> The your subroutine can be rewritten as follows
>
> subroutine test_recv (message)
>     real, target :: message(:,:)  !<-- assume it is contiguous
>
>     real, pointer :: remappedArray(:)
>
>    remappedArray => convertToRank1(message, size(message))
>
>    call MP_Recv (remappedArray, 2, MPI_INTEGER, 1, 1, MPI_COMM_WORLD,
> MPI_STATUS_IGNORE)
>
> end subroutine
>
>
> That only solves the problem if the assumed-shape is contiguous.  In F03
> we have bounds-remapping for pointers that converts (maps) rank one target
> to multi-dimension arrays.  I think that can be used if your test_recv()
> always expects a rank-one array assumed-shape dummy. You can map that
> array into a rank-n array using data pointer assignment to match the
> interface of MPI_Recv_wrapper, then you don't have the problems with
> generic resolution issues.
>
>
> Cheers,
>
> Jim Xia
>
> RL Fortran Compiler Test
> IBM Toronto Lab at 8200 Warden Ave, Markham, On, L6G 1C7
> Phone (905) 413-3444  Tie-line 313-3444
> email: jimxia at ca.ibm.com
> D2/YF7/8200 /MKM
>
>
>
> From:
> Craig Rasmussen <crasmussen at lanl.gov>
> To:
> MPI-3 Fortran working group <mpi3-fortran at lists.mpi-forum.org>
> Cc:
> WG5 <sc22wg5 at open-std.org>
> Date:
> 12/17/2008 10:45 AM
> Subject:
> (j3.2006) (SC22WG5.3823) Please tell me I'm wrong
>
>
>
> Without help from the Fortran standard, I don't think there is anyway to
> avoid a combinatorial explosion of interfaces (made worse by the F2008
> with 15 dimensions).  Consider the simple example code snippet:
>
> ---------
>
> subroutine test_recv(message)
>  real :: message(:,:)
>
>  call MPI_Recv(message, 2, MPI_INTEGER, 1, 1, MPI_COMM_WORLD,
> MPI_STATUS_IGNORE)
>
> end subroutine
>
> ---------
>
> For interface declaration:
>
> subroutine MPI_Recv_wrapper(buf, count, datatype, source, tag, comm,
> status, err)
>  real, dimension(*), intent(out)  :: buf
>
> or:
>
> subroutine MPI_Recv_wrapper(buf, count, datatype, source, tag, comm,
> status, err)
>  real, dimension(1,1,1,1,1,1,*), intent(out)  :: buf
>
> This give the following error with the Intel compiler:
>
> fortcom: Error: test_recv_call.f90, line 15: There is no matching specific
> subroutine for this generic subroutine call.   [MPI_RECV]
>  call MPI_Recv(message, 2, MPI_INTEGER, dest, 1, MPI_COMM_WORLD,
> MPI_STATUS_IGNORE)
> --------^
>
> On the other hand, if we use the interface:
>
> subroutine MPI_Recv_wrapper(buf, count, datatype, source, tag, comm,
> status, err)
>  type(C_PTR) :: buf
>
> There is still a problem as assumed shape arrays are not interoperable.
>>From gfortran:
>
>  call MPI_Recv(C_LOC(message), 2, MPI_INTEGER, dest, 1, MPI_COMM_WORLD,
> requ
>                                           1
> Error: Assumed-shape array 'message' at (1) cannot be an argument to the
> procedure 'c_loc because it is not C interoperable
>
>
> So there doesn't seem to be anyway to currently do multi-dimensional
> interfaces for assumed-shape actuals without a combinatorial explosion of
> interfaces.  This also seems to be the case for assumed-size actuals as
> well.
>
> Comments?
>
> Cheers,
> Craig
>
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