MPI_Comm_create_keyval(3)

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

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