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.TH "MPI_COMM_CREATE_KEYVAL" "3" "Jul 22, 2024" "" "Open MPI"
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\fI\%MPI_Comm_create_keyval\fP — Generates a new attribute key.
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#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)
.ft P
.fi
.UNINDENT
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.SS Fortran Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq

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
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.fi
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.SS Fortran 2008 Syntax
.INDENT 0.0
.INDENT 3.5
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.nf
.ft C
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
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.fi
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.SH INPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
.INDENT 2.0
.TP
.B \fBcomm_copy_attr_fn\fP
Copy callback function for \fBcomm_keyval\fP
(function).
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.IP \(bu 2
.INDENT 2.0
.TP
.B \fBcomm_delete_attr_fn\fP
Delete callback function for
\fBcomm_keyval\fP (function).
.UNINDENT
.IP \(bu 2
\fBextra_state\fP : Extra state for callback functions.
.UNINDENT
.SH OUTPUT PARAMETER
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.IP \(bu 2
\fBcomm_keyval\fP : Key value for future access (integer).
.IP \(bu 2
\fBierror\fP : Fortran only: Error status (integer).
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.SH DESCRIPTION
.sp
This function replaces \fI\%MPI_Keyval_create\fP, the use of which is
deprecated. The C binding is identical. The Fortran binding differs in
that \fBextra_state\fP is an address\-sized integer. Also, the copy and
delete callback functions have Fortran bindings that are consistent with
address\-sized attributes. The argument \fBcomm_copy_attr_fn\fP may be
specified as \fBMPI_COMM_NULL_COPY_FN\fP or \fBMPI_COMM_DUP_FN\fP from C or
Fortran. \fBMPI_COMM_NULL_COPY_FN\fP is a function that does nothing more
than returning \fBflag = 0\fP and \fBMPI_SUCCESS\fP\&. \fBMPI_COMM_DUP_FN\fP is
a simple\-minded copy function that sets \fBflag = 1\fP, returns the value
of \fBattribute_val_in\fP in \fBattribute_val_out\fP, and returns
\fBMPI_SUCCESS\fP\&. These replace the MPI\-1 predefined callbacks
\fBMPI_NULL_COPY_FN\fP and \fBMPI_DUP_FN\fP, the use of which is deprecated.
The two C callback functions are:
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.INDENT 3.5
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.nf
.ft C
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);

typedef int MPI_Comm_delete_attr_function(MPI_Comm comm, int comm_keyval,
             void *attribute_val, void *extra_state);
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.sp
which are the same as the MPI\-1.1 calls but with a new name. The old
names are deprecated. The two Fortran callback functions are:
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.nf
.ft C
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

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
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.fi
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.SH ERRORS
.sp
Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.
.sp
Before the error value is returned, the current MPI error handler associated
with the communication object (e.g., communicator, window, file) is called.
If no communication object is associated with the MPI call, then the call is
considered attached to MPI_COMM_SELF and will call the associated MPI error
handler. When MPI_COMM_SELF is not initialized (i.e., before
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
handler is called for all other MPI functions.
.sp
Open MPI includes three predefined error handlers that can be used:
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.IP \(bu 2
\fBMPI_ERRORS_ARE_FATAL\fP
Causes the program to abort all connected MPI processes.
.IP \(bu 2
\fBMPI_ERRORS_ABORT\fP
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
called on a window or file, acts as if \fI\%MPI_Abort\fP was called
on a communicator containing the group of processes in the
corresponding window or file. If called on a session,
aborts only the local process.
.IP \(bu 2
\fBMPI_ERRORS_RETURN\fP
Returns an error code to the application.
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.sp
MPI applications can also implement their own error handlers by calling:
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.IP \(bu 2
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
.IP \(bu 2
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
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Note that MPI does not guarantee that an MPI program can continue past
an error.
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See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
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See the Error Handling section of the MPI\-3.1 standard for
more information.
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\fBSEE ALSO:\fP
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.INDENT 3.5
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.IP \(bu 2
\fI\%MPI_Comm_free_keyval\fP
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.SH COPYRIGHT
2003-2024, The Open MPI Community
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