Provided by: openmpi-doc_5.0.7-1_all 
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
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 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 two 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);
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 two
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
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
ERRORS
Almost all MPI routines return an error value; C routines as the return result of the function and
Fortran routines in the last argument.
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 MPI_Init/MPI_Init_thread, after
MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler.
The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/‐
MPI_Comm_spawn_multiple. 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.
Open MPI includes three predefined error handlers that can be used:
• MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.
• MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a
window or file, acts as if MPI_Abort 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.
• MPI_ERRORS_RETURN Returns an error code to the application.
MPI applications can also implement their own error handlers by calling:
• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler
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 the Error Handling section of the MPI-3.1 standard for more information.
SEE ALSO:
• MPI_Comm_free_keyval
COPYRIGHT
2003-2025, The Open MPI Community
Feb 17, 2025 MPI_COMM_CREATE_KEYVAL(3)