MPI_TYPE_CREATE_KEYVAL(3)			     Open MPI				 MPI_TYPE_CREATE_KEYVAL(3)

MPI_Type_create_keyval — Generates a new attribute key for caching on data types.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Type_create_keyval(MPI_Type_copy_attr_function *type_copy_attr_fn,
	       MPI_Type_delete_attr_function *type_delete_attr_fn,
	       int *type_keyval, void *extra_state)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_TYPE_CREATE_KEYVAL(TYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN,
		       TYPE_KEYVAL, EXTRA_STATE, IERROR)
	       EXTERNAL TYPE_COPY_ATTR_FN, TYPE_DELETE_ATTR_FN
	       INTEGER TYPE_KEYVAL, IERROR
	       INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Type_create_keyval(type_copy_attr_fn, type_delete_attr_fn, type_keyval,
		       extra_state, ierror)
	       PROCEDURE(MPI_Type_copy_attr_function) :: type_copy_attr_fn
	       PROCEDURE(MPI_Type_delete_attr_function) :: type_delete_attr_fn
	       INTEGER, INTENT(OUT) :: type_keyval
	       INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: extra_state
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS
       • type_copy_attr_fn: Copy callback function for type_keyval (function).

       • type_delete_attr_fn: Delete callback function for type_keyval (function).

       • extra_state: Extra state for callback functions.

OUTPUT PARAMETERS
       • type_keyval: Key value for future access (integer).

       • ierror: Fortran only: Error status (integer).

DESCRIPTION
       MPI_Type_create_keyval  generates  a  new  attribute  key for caching on data types. This routine partially
       replaces MPI_Keyval_create <#mpi-keyval-create>.

       The argument type_copy_attr_fn may be specified as  MPI_TYPE_NULL_COPY_FN  or  MPI_TYPE_DUP_FN  from  C	or
       Fortran.	  MPI_TYPE_NULL_COPY_FN	 is  a	function  that	does  nothing  other  than  returning flag = 0 and
       MPI_SUCCESS. MPI_TYPE_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.

       The   argument  type_delete_attr_fn  may	 be  specified	as  MPI_TYPE_NULL_DELETE_FN  from  C  or  Fortran.
       MPI_TYPE_NULL_DELETE_FN is a function that does	nothing	 beyond	 returning  MPI_SUCCESS.  The  C  callback
       functions are:

	  typedef int MPI_Type_copy_attr_function(MPI_Datatype oldtype,
		      int type_keyval, void *extra_state, void *attribute_val_in,
		      void *attribute_val_out, int *flag);

	  typedef int MPI_Type_delete_attr_function(MPI_Datatype type, int type_keyval,
		       void *attribute_val, void *extra_state);

       The Fortran callback functions are:

	  SUBROUTINE TYPE_COPY_ATTR_FN(OLDTYPE, TYPE_KEYVAL, EXTRA_STATE,
		       ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, FLAG, IERROR)
	      INTEGER OLDTYPE, TYPE KEYVAL, IERROR
	      INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE,
		  ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT
	      LOGICAL FLAG

	  SUBROUTINE TYPE_DELETE_ATTR_FN(TYPE, TYPE_KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE,
		       IERROR)
	      INTEGER TYPE, TYPE_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>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#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 <#
       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>/MPI_Comm_spawn_multiple	<#
       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 <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#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	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

       See also:

	  • MPI_Type_free_keyval <#mpi-type-free-keyval>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				 MPI_TYPE_CREATE_KEYVAL(3)
