MPI_COMM_FREE_KEYVAL(3)				     Open MPI				   MPI_COMM_FREE_KEYVAL(3)

MPI_Comm_free_keyval — Frees attribute key for communicator cache attribute.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Comm_free_keyval(int *comm_keyval)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_COMM_FREE_KEYVAL(COMM_KEYVAL, IERROR)
	       INTEGER COMM_KEYVAL, IERROR

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Comm_free_keyval(comm_keyval, ierror)
	       INTEGER, INTENT(INOUT) :: comm_keyval
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT/OUTPUT PARAMETER
       • comm_keyval:

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

DESCRIPTION
       MPI_Comm_free_keyval   frees  an	 extant	 attribute  key.  This	function  sets	the  value  of	keyval	to
       MPI_KEYVAL_INVALID. Note that it is not erroneous to free an attribute key that	is  in	use,  because  the
       actual  free  does  not transpire until after all references (in other communicators on the process) to the
       key have been freed. These references need to be explicitly freed by  the  program,  either  via	 calls	to
       MPI_Comm_delete_attr <#mpi-comm-delete-attr> that free one attribute instance, or by calls to MPI_Comm_free
       <#mpi-comm-free> that free all attribute instances associated with the freed communicator.

       This  call  is  identical  to  the  call	 MPI_Keyval_free  <#mpi-keyval-free>  but  is  needed to match the
       communicator-specific creation function introduced in the MPI-2 standard. The  use  of  MPI_Keyval_free	<#
       mpi-keyval-free> is deprecated.

NOTES
       Key values are global (they can be used with any and all communicators).

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_Comm_create_keyval <#mpi-comm-create-keyval>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				   MPI_COMM_FREE_KEYVAL(3)
