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MPI_Comm_create_keyval(3)             MPI            MPI_Comm_create_keyval(3)


NAME

       MPI_Comm_create_keyval -  Create a new attribute key


SYNOPSIS

       int MPI_Comm_create_keyval(MPI_Comm_copy_attr_function *comm_copy_attr_fn,
                                MPI_Comm_delete_attr_function *comm_delete_attr_fn,
                                int *comm_keyval, void *extra_state)


INPUT PARAMETERS

       copy_fn
              - Copy callback function for keyval

       delete_fn
              - Delete callback function for keyval

       extra_state
              - Extra state for callback functions


OUTPUT PARAMETER

       comm_keyval
              - key value for future access (integer)


NOTES

       Key values are global (available for any and all communicators).

       Default copy and delete functions are available.  These are
       MPI_COMM_NULL_COPY_FN
              - empty copy function
       MPI_COMM_NULL_DELETE_FN
              - empty delete function
       MPI_COMM_DUP_FN
              - simple dup function

              There are subtle differences between C and Fortran that require
              that the copy_fn be written in the same language from which
              MPI_Comm_create_keyval is called.  This should not be a problem
              for most users; only programers using both Fortran and C in the
              same program need to be sure that they follow this rule.


RETURN VALUE FROM ATTRIBUTE CALLBACKS

       The MPI-2 versions of the attribute callbacks should return either
       MPI_SUCCESS on success or a valid MPI error code or class on failure.
       The MPI standard is ambiguous on this point, but as MPI-2 provides the
       routines MPI_Add_error_class and MPI_Add_error_code that allow the user
       to define and use MPI error codes and classes.


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 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.


SEE ALSO

       MPI_Comm_free_keyval


LOCATION

       src/mpi/attr/comm_create_keyval.c

                                   9/20/2012         MPI_Comm_create_keyval(3)

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