The MPI F08 binding interface, defi

The MPI F08 binding interface, defined in a module named
mpi_f08, has several big improvements over its ancestors.
The most important one is that choice buffers are now declared
as assumed-type, assumed-rank dummy arguments,
that is, of type type(*), dimension(..), which is defined
in TS 29113. The actual argument for an assumed-type,
assumed-rank dummy can be of any type and can be a scalar,
an array, or an array section (i.e., subarray). The subarray
can even be noncontiguous by using Fortran subscript
triplets, for example, a(2:10:2), where a is a 1-d array and
the subarray contains a(2) to a(10) with a stride of 2.
The F08 binding further improves type safety in various
aspects. MPI handles in the F77/F90 bindings all have type
integer, making them indistinguishable to compilers. In
the F08 binding, handles are defined as Fortran bind(C) derived
types that consist of only one element, integer ::
MPI_VAL. The internal handle value is identical to the Fortran
integer value used in the F77/F90 bindings. Operators
such as == and /= are overloaded to allow the comparison
of these handles. An MPI Status variable in the F77/F90
bindings is an integer array, for example, integer :: status(MPI_STATUS_SIZE).
In the F08 binding, it has a Fortran
bind(C) derived type with three public integer components,
MPI_SOURCE, MPI_TAG and MPI_ERROR, which are identical to
the Fortran integer value used in the F77/F90 bindings. Additionally,
the F08 binding defines interfaces for MPI userdefined
callback functions. Dummy arguments that are a
procedure (similar to function pointers in C) are declared
by using Fortran’s procedure keyword. Listing 1 shows some
types defined in the F08 binding.
type , bind (C) :: MPI_Comm
integer :: MPI_VAL
end type MPI_Comm
type , bind (C) :: MPI_Status
integer :: MPI_SOURCE
integer :: MPI_TAG
integer :: MPI_ERROR
... ! Implementation - dependant private components
end type MPI_Status
Listing 1: MPI F08 type examples
The F08 binding also declares the ierror argument in
all Fortran subroutines except user-defined and predefined
callbacks as optional, so that a programmer can omit that
argument. Additionally, choice buffers in nonblocking communications
now have an asynchronous attribute. In Fortran
2003/2008, this attribute could be used only to protect
buffers of Fortran asynchronous I/O. With TS 29113, this
attribute now also covers asynchronous communication occurring
within library routines.