NAME

       MPI_Comm_create_keyval - Generates a new attribute key.

SYNTAX

C Syntax

       #include <mpi.h>
       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)

Fortran Syntax (see FORTRAN 77 NOTES)

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_COMM_CREATE_KEYVAL(COMM_COPY_ATTR_FN, COMM_DELETE_ATTR_FN,
            COMM_KEYVAL, EXTRA_STATE, IERROR)

           EXTERNAL COMM_COPY_ATTR_FN, COMM_DELETE_ATTR_FN
           INTEGER COMM_KEYVAL, IERROR
           INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Comm_create_keyval(comm_copy_attr_fn, comm_delete_attr_fn, comm_keyval,
                 extra_state, ierror)
            PROCEDURE(MPI_Comm_copy_attr_function) :: comm_copy_attr_fn
            PROCEDURE(MPI_Comm_delete_attr_function) :: comm_delete_attr_fn
            INTEGER, INTENT(OUT) :: comm_keyval
            INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: extra_state
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror

C++ Syntax

       #include <mpi.h>
       static in MPI::Comm::Create_keyval(MPI::Comm::Copy_attr_function*
            comm_copy_attr_fn,
            MPI::Comm::Delete_attr_function* comm_delete_attr_fn,
            void* extra_state)

INPUT PARAMETERS

       comm_copy_attr_fn
                 Copy callback function for comm_keyval (function).

       comm_delete_attr_fn
                 Delete callback function for comm_keyval (function).

       extra_state
                 Extra state for callback functions.

OUTPUT PARAMETER

       comm_keyval
                 Key value for future access (integer).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       This function replaces MPI_Keyval_create, the use of which is deprecated. The C binding is
       identical. The Fortran binding differs in that extra_state is  an  address-sized  integer.
       Also,  the  copy  and  delete callback functions have Fortran bindings that are consistent
       with address-sized attributes.

       The  argument   comm_copy_attr_fn   may   be   specified   as   MPI_COMM_NULL_COPY_FN   or
       MPI_COMM_DUP_FN  from  C,  C++,  or Fortran. MPI_COMM_NULL_COPY_FN is a function that does
       nothing more than returning flag = 0 and MPI_SUCCESS. MPI_COMM_DUP_FN is  a  simple-minded
       copy   function   that   sets   flag  =  1,  returns  the  value  of  attribute_val_in  in
       attribute_val_out, and returns MPI_SUCCESS. These replace the MPI-1  predefined  callbacks
       MPI_NULL_COPY_FN and MPI_DUP_FN, the use of which is deprecated.

       The C callback functions are:

       typedef int MPI_Comm_copy_attr_function(MPI_Comm oldcomm, int comm_keyval,
                    void *extra_state, void *attribute_val_in,
                    void *attribute_val_out, int *flag);
       and
       typedef int MPI_Comm_delete_attr_function(MPI_Comm comm, int comm_keyval,
                    void *attribute_val, void *extra_state);

       which are the same as the MPI-1.1 calls but with a new name. The old names are deprecated.

       The Fortran callback functions are:

       SUBROUTINE COMM_COPY_ATTR_FN(OLDCOMM, COMM_KEYVAL, EXTRA_STATE,
                    ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, FLAG, IERROR)
           INTEGER OLDCOMM, COMM_KEYVAL, IERROR
           INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE, ATTRIBUTE_VAL_IN,
               ATTRIBUTE_VAL_OUT
           LOGICAL FLAG
       and
       SUBROUTINE COMM_DELETE_ATTR_FN(COMM, COMM_KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE,
                    IERROR)
           INTEGER COMM, COMM_KEYVAL, IERROR
           INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE_VAL, EXTRA_STATE

       The C++ callbacks are:

       typedef int MPI::Comm::Copy_attr_function(const MPI::Comm& oldcomm,
                    int comm_keyval, void* extra_state, void* attribute_val_in,
                    void* attribute_val_out, bool& flag);
       and
       typedef int MPI::Comm::Delete_attr_function(MPI::Comm& comm,
                    int comm_keyval, void* attribute_val, void* extra_state);

FORTRAN 77 NOTES

       The  MPI standard prescribes portable Fortran syntax for the EXTRA_STATE argument only for
       Fortran 90. FORTRAN 77 users may use the non-portable syntax

            INTEGER*MPI_ADDRESS_KIND EXTRA_STATE

       where MPI_ADDRESS_KIND is a constant defined  in  mpif.h  and  gives  the  length  of  the
       declared integer in bytes.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran routines in the last argument. C++ functions do not return errors. If the  default
       error  handler  is  set  to  MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception
       mechanism will be used to throw an MPI::Exception object.

       Before the error value is returned, the current MPI error handler is called.  By  default,
       this  error  handler aborts the MPI job, except for I/O function errors. The error handler
       may   be   changed   with   MPI_Comm_set_errhandler;   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.

       See the MPI man page for a full list of MPI error codes.

SEE ALSO