int MPI_Comm_set_attr(
  MPI_Comm comm,
  int comm_keyval,
  void *attribute_val
);

Parameters

comm

[in] communicator to which attribute will be attached (handle)

keyval

[in] key value, as returned by MPI_Comm_create_keyval (integer)

attribute_val

[in] attribute value

Remarks

Values of the permanent attributes MPI_TAG_UB, MPI_HOST, MPI_IO, MPI_WTIME_IS_GLOBAL, MPI_UNIVERSE_SIZE, MPI_LASTUSEDCODE, and MPI_APPNUM may not be changed.

The type of the attribute value depends on whether C, C++, or Fortran is being used. In C and C++, an attribute value is a pointer (void *); in Fortran, it is an address-sized integer.

If an attribute is already present, the delete function (specified when the corresponding keyval was created) will be called.

This function replaces MPI_ATTR_PUT, whose use is deprecated. The C binding is identical. The Fortran binding differs in that attribute_val is an address-sized integer.

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

Notes for Fortran

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.

Errors

All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS

No error; MPI routine completed successfully.

MPI_ERR_COMM

Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).

MPI_ERR_KEYVAL

Invalid keyval

MPI_ERR_ARG

This error class is associated with an error code that indicates that an attempt was made to free one of the permanent keys.

See Also

Example Code

The following sample code illustrates MPI_Comm_set_attr.

#include "mpi.h"
#include <stdio.h>

/* Test creating and inserting attributes in different orders to ensure that the list management code handles all cases. */
int checkAttrs( MPI_Comm comm, int n, int key[], int attrval[] );
int checkNoAttrs( MPI_Comm comm, int n, int key[] );

int main( int argc, char *argv[] )
{
    int errs = 0;
    int key[3], attrval[3];
    int i;
    MPI_Comm comm;

    MPI_Init( &argc, &argv );
    comm = MPI_COMM_WORLD;
    /* Create key values */
    for (i=0; i<3; i++) {
        MPI_Comm_create_keyval( MPI_NULL_COPY_FN, MPI_NULL_DELETE_FN, &key[i], (void *)0 );
        attrval[i] = 1024 * i;
    }

    /* Insert attribute in several orders. Test after put with get, then delete, then confirm delete with get. */
    MPI_Comm_set_attr( comm, key[2], &attrval[2] );
    MPI_Comm_set_attr( comm, key[1], &attrval[1] );
    MPI_Comm_set_attr( comm, key[0], &attrval[0] );
    errs += checkAttrs( comm, 3, key, attrval );

    MPI_Comm_delete_attr( comm, key[0] );
    MPI_Comm_delete_attr( comm, key[1] );
    MPI_Comm_delete_attr( comm, key[2] );
    errs += checkNoAttrs( comm, 3, key );

    MPI_Comm_set_attr( comm, key[1], &attrval[1] );
    MPI_Comm_set_attr( comm, key[2], &attrval[2] );
    MPI_Comm_set_attr( comm, key[0], &attrval[0] );
    errs += checkAttrs( comm, 3, key, attrval );

    MPI_Comm_delete_attr( comm, key[2] );
    MPI_Comm_delete_attr( comm, key[1] );
    MPI_Comm_delete_attr( comm, key[0] );
    errs += checkNoAttrs( comm, 3, key );

    MPI_Comm_set_attr( comm, key[0], &attrval[0] );
    MPI_Comm_set_attr( comm, key[1], &attrval[1] );
    MPI_Comm_set_attr( comm, key[2], &attrval[2] );
    errs += checkAttrs( comm, 3, key, attrval );

    MPI_Comm_delete_attr( comm, key[1] );
    MPI_Comm_delete_attr( comm, key[2] );
    MPI_Comm_delete_attr( comm, key[0] );
    errs += checkNoAttrs( comm, 3, key );

    for (i=0; i<3; i++) {
        MPI_Comm_free_keyval( &key[i] );
    }
    MPI_Finalize();
    return 0;
}

int checkAttrs( MPI_Comm comm, int n, int key[], int attrval[] )
{
    int errs = 0;
    int i, flag, *val_p;
    for (i=0; i<n; i++) {
        MPI_Comm_get_attr( comm, key[i], &val_p, &flag );
        if (!flag) {
            errs++;
            fprintf( stderr, "Attribute for key %d not set\n", i );fflush(stderr);
        }
        else if (val_p != &attrval[i]) {
            errs++;
            fprintf( stderr, "Atribute value for key %d not correct\n", i );fflush(stderr);
        }
    }
    return errs;
}

int checkNoAttrs( MPI_Comm comm, int n, int key[] )
{
    int errs = 0;
    int i, flag, *val_p;
    for (i=0; i<n; i++) {
        MPI_Comm_get_attr( comm, key[i], &val_p, &flag );
        if (flag) {
            errs++;
            fprintf( stderr, "Attribute for key %d set but should be deleted\n", i );fflush(stderr);
        }
    }
    return errs;
}