int MPI_Attr_get(
  MPI_Comm comm,
  int keyval,
  void *attr_value,
  int *flag
);

Parameters

comm

[in] communicator to which attribute is attached (handle)

keyval

[in] key value (integer)

attr_value

[out] attribute value, unless flag = false

flag

[out] true if an attribute value was extracted; false if no attribute is associated with the key

Remarks

Retrieves attribute value by key. The call is erroneous if there is no key with value keyval. On the other hand, the call is correct if the key value exists, but no attribute is attached on comm for that key; in such case, the call returns flag = false. In particular MPI_KEYVAL_INVALID is an erroneous key value.

Advice to users.

The call to MPI_Attr_put passes in attribute_val the value of the attribute; the call to MPI_Attr_get passes in attribute_val the address of the the location where the attribute value is to be returned. Thus, if the attribute value itself is a pointer of type void*, the the actual attribute_val parameter to MPI_Attr_put will be of type void* and the actual attribute_val parameter to MPI_Attr_put will be of type void**.

Notes for C

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.

Deprecated Function

Notes for Fortran

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

The attr_value in Fortran is a pointer to a Fortran integer, not a pointer to a void *.

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

See Also

Example Code

The following sample code illustrates MPI_Attr_get.

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

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_Keyval_create( 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_Attr_put( comm, key[2], &attrval[2] );
    MPI_Attr_put( comm, key[1], &attrval[1] );
    MPI_Attr_put( comm, key[0], &attrval[0] );

    errs += checkAttrs( comm, 3, key, attrval );

    MPI_Attr_delete( comm, key[0] );
    MPI_Attr_delete( comm, key[1] );
    MPI_Attr_delete( comm, key[2] );

    errs += checkNoAttrs( comm, 3, key );

    MPI_Attr_put( comm, key[1], &attrval[1] );
    MPI_Attr_put( comm, key[2], &attrval[2] );
    MPI_Attr_put( comm, key[0], &attrval[0] );

    errs += checkAttrs( comm, 3, key, attrval );

    MPI_Attr_delete( comm, key[2] );
    MPI_Attr_delete( comm, key[1] );
    MPI_Attr_delete( comm, key[0] );

    errs += checkNoAttrs( comm, 3, key );

    MPI_Attr_put( comm, key[0], &attrval[0] );
    MPI_Attr_put( comm, key[1], &attrval[1] );
    MPI_Attr_put( comm, key[2], &attrval[2] );

    errs += checkAttrs( comm, 3, key, attrval );

    MPI_Attr_delete( comm, key[1] );
    MPI_Attr_delete( comm, key[2] );
    MPI_Attr_delete( comm, key[0] );

    errs += checkNoAttrs( comm, 3, key );

    for (i=0; i<3; i++) {
        MPI_Keyval_free( &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_Attr_get( 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_Attr_get( 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;
}