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NAME

MPI_Attr_get - Retrieve an attribute attached to a keyval for a communicator

SYNOPSIS

#include <mpi.h> int MPI_Attr_get(MPI_Comm comm , int keyval , void *attr , int *flag );

#include <pmpi.h> int PMPI_Attr_get(MPI_Comm comm , int keyval , void *attr , int *flag );

INCLUDE 'mpif.h' MPI_ATTR_GET(comm , keyval , attr , flag , ierr ) INTEGER comm , keyval , attr , flag , ierr

INPUT PARAMETERS

comm - communicator (handle)

keyval - key value (handle)

OUTPUT PARAMETERS

attr - attribute (void pointer in C, integer in FORTRAN)

flag - did the attribute exist (boolean)

DESCRIPTION

The MPI_Attr_get() function is used to retrieve an attribute, attr attached to a keyval for a given communicator, comm . The attribute can be set with the MPI_Attr_put() function, and deleted with the MPI_Attr_delete() function.

If there was an attribute attached, then flag is set to one. Otherwise, it is set to zero.

Note that even though the attr parameter's type in C is void *, it should be viewed as a void **. The other type is chosen to ease use of this functions and avoid excess type casting. In FORTRAN, the attribute is an integer, and will return the bottom 32 bits of a C attribute void pointer if there was one attached.

The behaviour of attributes under the copying or deleting of communicators is defined by the keyval in MPI_Keyval_create().

PMPI_Attr_get() is the profiling version of this function.

ERRORS

All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.

In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.

MPI_SUCCESS - No error;

MPI_ERR_PENDING - Pending exception;

MPI_ERR_COMM - Invalid communicator;

MPI_ERR_KEYVAL - Invalid keyval.

SEE ALSO

MPI_Keyval_create (3) MPI_Keyval_free (3) MPI_Attr_put (3) MPI_Attr_delete (3)

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