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

[Jim Xia]

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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