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

       comm_copy_attr_fn
              - Copy callback function for keyval

       comm_delete_attr_fn
              - Delete callback function for keyval

       extra_state
              - Extra state for callback functions

OUTPUT PARAMETERS

       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 programmers 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

                                            11/9/2015                   MPI_Comm_create_keyval(3)