NAME

       MPI_Keyval_create - Generates a new attribute key -- use of this routine is deprecated.

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Keyval_create(MPI_Copy_function *copy_fn,
            MPI_Delete_function *delete_fn, int *keyval, void *extra_state)

Fortran Syntax

       INCLUDE 'mpif.h'
       MPI_KEYVAL_CREATE(COPY_FN, DELETE_FN, KEYVAL, EXTRA_STATE, IERROR)
            EXTERNAL  COPY_FN, DELETE_FN
            INTEGER   KEYVAL, EXTRA_STATE, IERROR

INPUT PARAMETERS

       copy_fn   Copy callback function for keyval.

       delete_fn Delete callback function for keyval.

       extra_state
                 Extra state for callback functions.

OUTPUT PARAMETERS

       keyval    Key value for future access (integer).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       Note that use of this routine is deprecated as of MPI-2. Please use MPI_Comm_create_keyval instead.

       This deprecated routine is not available in C++.

       Generates  a  new attribute key. Keys are locally unique in a process and opaque to the user, though they
       are explicitly stored in integers. Once allocated, the key value can be used to associate attributes  and
       access them on any locally defined communicator.

       The  copy_fn  function is invoked when a communicator is duplicated by MPI_COMM_DUP. copy_fn should be of
       type MPI_Copy_function, which is defined as follows:

         typedef int MPI_Copy_function(MPI_Comm oldcomm, int keyval,
                                       void *extra_state, void *attribute_val_in,
                                       void *attribute_val_out, int *flag)

       A Fortran declaration for such a function is as follows:

         SUBROUTINE COPY_FUNCTION(OLDCOMM, KEYVAL, EXTRA_STATE, ATTRIBUTE_VAL_IN,
                     ATTRIBUTE_VAL_OUT, FLAG, IERR)
         INTEGER OLDCOMM, KEYVAL, EXTRA_STATE,
         ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, IERR
         LOGICAL FLAG

       The copy callback function is invoked for each key value in oldcomm in arbitrary order. Each call to  the
       copy  callback is made with a key value and its corresponding attribute. If it returns flag = 0, then the
       attribute is deleted in the duplicated communicator. Otherwise ( flag = 1), the new  attribute  value  is
       set  to the value returned in attribute_val_out. The function returns MPI_SUCCESS on success and an error
       code on failure (in which case MPI_Comm_dup will fail).

       copy_fn may be specified as MPI_NULL_COPY_FN or MPI_DUP_FN from either C or Fortran; MPI_NULL_COPY_FN  is
       a  function  that does nothing other than return flag = 0, and MPI_SUCCESS. MPI_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.

NOTES

       Key values are global (available for any and all communicators).

       There are subtle differences between C and Fortran that require that the copy_fn be written in  the  same
       language  that  MPI_Keyval_create  is  called  from.  This  should  not be a problem for most users; only
       programmers using both Fortran and C in the same program need to be sure that they follow this rule.

       Even though both formal arguments attribute_val_in and attribute_val_out are of type void*,  their  usage
       differs.  The  C  copy  function  is passed by MPI in attribute_val_in the value of the attribute, and in
       attribute_val_out the address of the attribute, so as to allow the function to return the (new) attribute
       value. The use of type void* for both is to avoid messy type casts.

       A valid copy function is one that completely duplicates the information by making a full  duplicate  copy
       of  the  data  structures implied by an attribute; another might just make another reference to that data
       structure, while using a reference-count mechanism. Other types of attributes might not copy at all (they
       might be specific to oldcomm only).

       Analogous to copy_fn is a callback deletion function, defined  as  follows.  The  delete_fn  function  is
       invoked  when  a  communicator  is  deleted  by  MPI_Comm_free  or  when  a  call  is  made explicitly to
       MPI_Attr_delete. delete_fn should be of type MPI_Delete_function, which is defined as follows:

         typedef int MPI_Delete_function(MPI_Comm comm, int keyval,
             void *attribute_val, void *extra_state);

       A Fortran declaration for such a function is as follows:

         SUBROUTINE DELETE_FUNCTION(COMM, KEYVAL,ATTRIBUTE_VAL, EXTRA_STATE, IERR)
             INTEGER COMM, KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE, IERR

       This function is called by MPI_Comm_free, MPI_Attr_delete, and MPI_Attr_put to do whatever is  needed  to
       remove  an  attribute. The function returns MPI_SUCCESS on success and an error code on failure (in which
       case MPI_COMM_FREE will fail).

       delete_fn may be specified as MPI_NULL_DELETE_FN from  either  C  or  FORTRAN;  MPI_NULL_DELETE_FN  is  a
       function that does nothing, other than returning MPI_SUCCESS.

       The  special  key  value  MPI_KEYVAL_INVALID is never returned by MPI_Keyval_create. Therefore, it can be
       used for static initialization of key values.

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 ALSO

       MPI_Keyval_free
       MPI_Comm_create_keyval

4.1.6                                             Sep 30, 2023                              MPI_Keyval_create(3)