10.2.4. Extended Fortran Support

Implementations with Extended Fortran support must provide:

1. An mpi module
2. A new set of functions to provide additional support for Fortran intrinsic numeric types, including parameterized types: MPI_SIZEOF, MPI_TYPE_MATCH_SIZE, MPI_TYPE_CREATE_F90_INTEGER, MPI_TYPE_CREATE_F90_REAL and MPI_TYPE_CREATE_F90_COMPLEX. Parameterized types are Fortran intrinsic types which are specified using KIND type parameters. These routines are described in detail in Section Additional Support for Fortran Numeric Intrinsic Types .

10.2.4.1. The mpi Module

An MPI implementation must provide a module named mpi that can be USEd in a Fortran 90 program. This module must:

• Define all named MPI constants
• Declare MPI functions that return a value.

• Provide interfaces for all or for a subset of MPI routines.
• Provide INTENT information in these interface blocks.

The appropriate INTENT may be different from what is given in the MPI generic interface. Implementations must choose INTENT so that the function adheres to the MPI standard. ( End of advice to implementors.)

Rationale.

The intent given by the MPI generic interface is not precisely defined and does not in all cases correspond to the correct Fortran INTENT. For instance, receiving into a buffer specified by a datatype with absolute addresses may require associating MPI_BOTTOM with a dummy OUT argument. Moreover, ``constants'' such as MPI_BOTTOM and MPI_STATUS_IGNORE are not constants as defined by Fortran, but ``special addresses'' used in a nonstandard way. Finally, the MPI-1 generic intent is changed in several places by MPI-2. For instance, MPI_IN_PLACE changes the sense of an OUT argument to be INOUT. ( End of rationale.)

Applications may use either the mpi module or the mpif.h include file. An implementation may require use of the module to prevent type mismatch errors (see below).
Advice to users.

It is recommended to use the mpi module even if it is not necessary to use it to avoid type mismatch errors on a particular system. Using a module provides several potential advantages over using an include file. ( End of advice to users.)
It must be possible to link together routines some of which USE mpi and others of which INCLUDE mpif.h.

10.2.4.2. No Type Mismatch Problems for Subroutines with Choice Arguments

A high quality MPI implementation should provide a mechanism to ensure that MPI choice arguments do not cause fatal compile-time or run-time errors due to type mismatch. An MPI implementation may require applications to use the mpi module, or require that it be compiled with a particular compiler flag, in order to avoid type mismatch problems.

Advice to implementors.

In the case where the compiler does not generate errors, nothing needs to be done to the existing interface. In the case where the compiler may generate errors, a set of overloaded functions may be used. See the paper of M. Hennecke [8]. Even if the compiler does not generate errors, explicit interfaces for all routines would be useful for detecting errors in the argument list. Also, explicit interfaces which give INTENT information can reduce the amount of copying for BUF(*) arguments. ( End of advice to implementors.)