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

4.1.6                                             Sep 30, 2023                         MPI_Comm_create_keyval(3)