NAME

MPI_Comm_get_attr - Retrieves attribute value by key

SYNOPSIS

int MPI_Comm_get_attr(MPI_Comm comm, int comm_keyval, void *attribute_val, int *flag)

INPUT PARAMETERS

comm: - communicator to which attribute is attached (handle)
comm_keyval: - key value (integer)

OUTPUT PARAMETERS

attribute_val: - attribute value, unless flag = false
flag: - true if an attribute value was extracted; false if no attribute is associated with the key

NOTES

Attributes must be extracted from the same language as they were inserted in with MPI_Comm_set_attr . The notes for C and Fortran below explain why.

NOTES FOR C

Even though the attr_value argument is declared as void * , it is really the address of a void pointer. See the rationale in the standard for more details.

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 routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

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 guarantee 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