.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines
.\" $COPYRIGHT$
.TH MPI_Type_create_keyval 3 "May 26, 2022" "4.1.4" "Open MPI"
.SH NAME
\fBMPI_Type_create_keyval\fP \- Generates a new attribute key for caching on data types.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Type_create_keyval(MPI_Type_copy_attr_function *\fItype_copy_attr_fn\fP,
	MPI_Type_delete_attr_function *\fItype_delete_attr_fn\fP,
	int *\fItype_keyval\fP, void *\fIextra_state\fP)

.fi
.SH Fortran Syntax (see FORTRAN 77 NOTES)
.nf
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TYPE_CREATE_KEYVAL(\fITYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN,
		TYPE_KEYVAL, EXTRA_STATE, IERROR\fP)
	EXTERNAL \fITYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN\fP
	INTEGER	\fITYPE_KEYVAL, IERROR \fP
	INTEGER(KIND=MPI_ADDRESS_KIND) \fIEXTRA_STATE\fP

.fi
.SH Fortran 2008 Syntax
.nf
USE mpi_f08
MPI_Type_create_keyval(\fItype_copy_attr_fn\fP, \fItype_delete_attr_fn\fP, \fItype_keyval\fP,
		\fIextra_state\fP, \fIierror\fP)
	PROCEDURE(MPI_Type_copy_attr_function) :: \fItype_copy_attr_fn\fP
	PROCEDURE(MPI_Type_delete_attr_function) :: \fItype_delete_attr_fn\fP
	INTEGER, INTENT(OUT) :: \fItype_keyval\fP
	INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: \fIextra_state\fP
	INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP

.fi
.SH C++ Syntax
.nf
#include <mpi.h>
static int MPI::Datatype::Create_keyval(MPI::Datatype::Copy_attr_function*
	\fItype_copy_attr_fn\fP, MPI::Datatype::Delete_attr_function*
	\fItype_delete_attr_fn\fP, void* \fIextra_state\fP)

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
type_copy_attr_fn
Copy callback function for \fItype_keyval\fP (function).
.TP 1i
type_delete_attr_fn
Delete callback function for \fItype_keyval\fP (function).
.TP 1i
extra_state
Extra state for callback functions.

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
type_keyval
Key value for future access (integer).
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
MPI_Type_create_keyval generates a new attribute key for caching on data types. This routine partially replaces MPI_Keyval_create.
.sp
The argument \fItype_copy_attr_fn\fP may be specified as MPI_TYPE_NULL_COPY_FN or MPI_TYPE_DUP_FN from C, C++, or Fortran. MPI_TYPE_NULL_COPY_FN is a function that does nothing other than returning \fIflag\fP = 0 and MPI_SUCCESS. MPI_TYPE_DUP_FN is a simple-minded copy function that sets \fIflag\fP = 1, returns the value of \fIattribute_val_in\fP in \fIattribute_val_out\fP, and returns MPI_SUCCESS.
.sp
The argument \fItype_delete_attr_fn\fP may be specified as MPI_TYPE_NULL_DELETE_FN from C, C++, or Fortran. MPI_TYPE_NULL_DELETE_FN is a function that does nothing beyond returning MPI_SUCCESS.
The C callback functions are:
.sp
.nf
typedef int MPI_Type_copy_attr_function(MPI_Datatype \fIoldtype\fP,
            int \fItype_keyval\fP, void *\fIextra_state\fP, void *\fIattribute_val_in\fP,
            void *\fIattribute_val_out\fP, int *\fIflag\fP);
.fi
and
.nf
typedef int MPI_Type_delete_attr_function(MPI_Datatype \fItype\fP, int \fItype_keyval\fP,
             void *\fIattribute_val\fP, void *\fIextra_state\fP);
.fi
.sp
The Fortran callback functions are:
.sp
.nf
SUBROUTINE TYPE_COPY_ATTR_FN(\fIOLDTYPE, TYPE_KEYVAL, EXTRA_STATE,
             ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, FLAG, IERROR\fP)
    INTEGER \fIOLDTYPE, TYPE KEYVAL, IERROR\fP
    INTEGER(KIND=MPI_ADDRESS_KIND) \fIEXTRA_STATE,
        ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT\fP
    LOGICAL \fIFLAG\fP
.fi
and
.nf
SUBROUTINE TYPE_DELETE_ATTR_FN(\fITYPE, TYPE_KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE,
             IERROR\fP)
    INTEGER \fITYPE, TYPE_KEYVAL, IERROR\fP
    INTEGER(KIND=MPI_ADDRESS_KIND) \fIATTRIBUTE VAL, EXTRA_STATE\fP
.fi
.sp
The C++ callbacks are:
.sp
.nf
typedef int MPI::Datatype::Copy_attr_function(const MPI::Datatype& \fIoldtype\fP,
             int \fItype_keyval\fP, void* \fIextra_state\fP,
             const void* \fIattribute_val_in\fP, void* \fIattribute_val_out\fP,
             bool& \fIflag\fP);
.fi
and
.nf
typedef int MPI::Datatype::Delete_attr_function(MPI::Datatype& \fItype\fP,
             int \fItype_keyval\fP, void* \fIattribute_val\fP, void* \fIextra_state\fP);
.fi
.sp

.SH FORTRAN 77 NOTES
.ft R
The MPI standard prescribes portable Fortran syntax for
the \fIEXTRA_STATE\fP argument only for Fortran 90.  FORTRAN 77
users may use the non-portable syntax
.sp
.nf
     INTEGER*MPI_ADDRESS_KIND \fIEXTRA_STATE\fP
.fi
.sp
where MPI_ADDRESS_KIND is a constant defined in mpif.h
and gives the length of the declared integer in bytes.

.SH 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.
.sp
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.

.SH SEE ALSO
.ft R
.sp
MPI_Type_free_keyval