MPI_WIN_FENCE(3)				     Open MPI					  MPI_WIN_FENCE(3)

MPI_Win_fence — Synchronizes RMA calls on a window.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Win_fence(int assert, MPI_Win win)

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

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Win_fence(assert, win, ierror)
	       INTEGER, INTENT(IN) :: assert
	       TYPE(MPI_Win), INTENT(IN) :: win
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS
       • assert: Program assertion (integer).

       • win: Window object (handle).

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

DESCRIPTION
       MPI_Win_fence synchronizes RMA calls on win. The call is collective on the group of win. All RMA operations
       on  win	originating  at	 a  given  process and started before the fence call will complete at that process
       before the fence call returns. They will be completed at their target before the fence call returns at  the
       target.	RMA  operations	 on win started by a process after the fence call returns will access their target
       window only after MPI_Win_fence has been called by the target process.

       The call completes an RMA access epoch if it was preceded by another  fence  call  and  the  local  process
       issued  RMA communication calls on win between these two calls. The call completes an RMA exposure epoch if
       it was preceded by another fence call and the local window was the target of RMA accesses between these two
       calls. The call starts an RMA access epoch if it is followed by another fence call and by RMA communication
       calls issued between these two fence calls. The call starts an exposure epoch if it is followed by  another
       fence  call  and	 the  local  window is the target of RMA accesses between these two fence calls. Thus, the
       fence call is equivalent to calls to a subset of post, start, complete, wait.

       The assert argument is used to provide assertions on the context of

       the call that may be used for various optimizations. A value of assert ^ 0 is always valid.  The	 following
       assertion value is supported:

       MPI_MODE_NOPRECEDE
	      No  local RMA calls have been issued before this fence. This assertion must be provided by all or no
	      members of the group of the window.  It  may  enable  faster  fence  call	 by  avoiding  unnecessary
	      synchronization.

       MPI_MODE_NOSTORE
	      Informs that the local window was not updated by local stores or get calls in the preceding epoch.

       MPI_MODE_NOPUT
	      Informs  that  the  local	 window will not be updated by any put or accummulate calls in the ensuing
	      epoch (until next fence call).

       MPI_MODE_NOSUCCEED
	      No local RMA calls will be issued after this fence. This assertion must be provided  by  all  or	no
	      members  of  the	group  of  the	window.	 It  may  enable faster fence call by avoiding unnecessary
	      synchronization.

NOTE
       Calls to MPI_Win_fence should both precede and follow calls to put, get or accumulate that are synchronized
       with fence calls.

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_Win_create <#mpi-win-create>

	  • MPI_Win_start <#mpi-win-start>

	  • MPI_Win_post <#mpi-win-post>

	  • MPI_Win_complete <#mpi-win-complete>

	  • MPI_Win_wait <#mpi-win-wait>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					  MPI_WIN_FENCE(3)
