MPI_COMM_SET_ATTR(3)				     Open MPI				      MPI_COMM_SET_ATTR(3)

MPI_Comm_set_attr — Stores attribute value associated with a key.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Comm_set_attr(MPI_Comm comm, int comm_keyval, void *attribute_val)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_COMM_SET_ATTR(COMM, COMM_KEYVAL, ATTRIBUTE_VAL, IERROR)
	       INTEGER COMM, COMM_KEYVAL, IERROR
	       INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE_VAL

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Comm_set_attr(comm, comm_keyval, attribute_val, ierror)
	       TYPE(MPI_Comm), INTENT(IN) :: comm
	       INTEGER, INTENT(IN) :: comm_keyval
	       INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: attribute_val
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT/OUTPUT PARAMETER
       • comm: Communicator from which attribute will be attached (handle).

INPUT PARAMETERS
       • comm_keyval: Key value (integer).

       • attribute_val: Attribute value.

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

DESCRIPTION
       MPI_Comm_set_attr  stores  the  stipulated  attribute  value  attribute_val  for	 subsequent  retrieval	by
       MPI_Comm_get_attr <#mpi-comm-get-attr>. If the value  is	 already  present,  then  the  outcome	is  as	if
       MPI_Comm_delete_attr  <#mpi-comm-delete-attr>  was  first  called  to  delete  the  previous value (and the
       callback function delete_fn was executed), and a new value was next stored. The call is erroneous if  there
       is no key with value comm_keyval; in particular MPI_KEYVAL_INVALID is an erroneous key value. The call will
       fail if the delete_fn function returned an error code other than MPI_SUCCESS.

       This  function  replaces	 MPI_Attr_put  <#mpi-attr-put>,	 the  use of which is deprecated. The C binding is
       identical. The Fortran binding differs in that attribute_val is an address-sized integer.

NOTES
       Values of the permanent attributes  MPI_TAG_UB,	MPI_HOST,  MPI_IO,  and	 MPI_WTIME_IS_GLOBAL  may  not	be
       changed.

       The  type of the attribute value depends on whether C or Fortran is being used. In C, an attribute value is
       a pointer (void *); in Fortran, it is a single, address-size integer system for which a	pointer	 does  not
       fit in an integer.

       If  an  attribute  is  already  present,	 the  delete function (specified when the corresponding keyval was
       created) will be called.

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.

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				      MPI_COMM_SET_ATTR(3)
