MPI Subroutine Reference

MPI_ATTR_PUT, MPI_Attr_put

Purpose

Stores an attribute value in a communicator.

C synopsis

#include <mpi.h>
int MPI_Attr_put(MPI_Comm comm,int keyval,void* attribute_val);

FORTRAN synopsis

include 'mpif.h' or use mpi
MPI_ATTR_PUT(INTEGER COMM,INTEGER KEYVAL,INTEGER ATTRIBUTE_VAL,
	     INTEGER IERROR)

Parameters

comm

is the communicator to which attribute will be attached (handle) (IN)

keyval

is the key value as returned by MPI_KEYVAL_CREATE (integer) (IN)

attribute_val

is the attribute value (IN)

IERROR

is the FORTRAN return code. It is always the last argument.

Description

This subroutine stores the attribute value for retrieval by MPI_ATTR_GET. Any previous value is deleted with the attribute delete_fn being called and the new value is stored. If there is no key with value keyval, the call is erroneous.

Notes

MPI_COMM_SET_ATTR supersedes MPI_ATTR_PUT.

MPI_ATTR_PUT does not interoperate with MPI_COMM_SET_ATTR. The FORTRAN bindings for MPI-1 caching functions presume that an attribute is an INTEGER. The MPI-2 caching bindings use INTEGER (KIND=MPI_ADDRESS_KIND). In an MPI implementation that uses 64-bit addresses and 32-bit INTEGERS, the two formats would be incompatible.

The implementation of MPI_ATTR_PUT and MPI_ATTR_GET involves saving a single word of information in the communicator. The languages C and FORTRAN have different approaches to using this capability:

In C: As the programmer, you normally define a struct that holds arbitrary "attribute" information. Before calling MPI_ATTR_PUT, you allocate some storage for the attribute structure and then call MPI_ATTR_PUT to record the address of this structure. You must make sure that the structure remains intact as long as it may be useful. As the programmer, you will also declare a variable of type "pointer to attribute structure" and pass the address of this variable when calling MPI_ATTR_GET. Both MPI_ATTR_PUT and MPI_ATTR_GET take a void* parameter, but this does not imply that the same parameter is passed to either one.

In FORTRAN: MPI_ATTR_PUT records an INTEGER*4 and MPI_ATTR_GET returns the INTEGER*4. As the programmer, you can choose to encode all attribute information in this integer or maintain some kind of database in which the integer can index. Either of these approaches will port to other MPI implementations.

XL FORTRAN has an additional feature that will allow some of the same functions a C programmer would use. This is the POINTER type, which is described in the IBM XL FORTRAN Compiler for AIX Language Reference. Use of this feature will impact the program's portability.

Errors

A delete_fn did not return MPI_SUCCESS

Invalid communicator

Invalid keyval

keyval is undefined

Predefined keyval

cannot modify predefined attributes

MPI not initialized

MPI already finalized

Related information

MPI_COMM_COPY_ATTR_FUNCTION

MPI_COMM_CREATE_KEYVAL

MPI_COMM_DELETE_ATTR

MPI_COMM_DELETE_ATTR_FUNCTION

MPI_COMM_GET_ATTR