# 17.2.440. MPI_Win_fence

MPI_Win_fence — Synchronizes RMA calls on a window.

## 17.2.440.1. SYNTAX

### 17.2.440.1.1. C Syntax

    #include <mpi.h>

    int MPI_Win_fence(int assert, MPI_Win win)

### 17.2.440.1.2. Fortran Syntax

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

### 17.2.440.1.3. 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

## 17.2.440.2. INPUT PARAMETERS

- `assert`: Program assertion (integer).

- `win`: Window object (handle).

## 17.2.440.3. OUTPUT PARAMETER

- `ierror`: Fortran only: Error status (integer).

## 17.2.440.4. 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.

## 17.2.440.5. NOTE

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

## 17.2.440.6. 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_thread, after 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 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_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 was called on that communicator. If called on a window or file, acts as if 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 then MPI_Comm_set_errhandler

- MPI_File_create_errhandler then MPI_File_set_errhandler

- MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

- MPI_Win_create_errhandler then MPI_Win_set_errhandler

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

See the MPI man page for a full list of MPI error codes.

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

See also

- MPI_Win_create

- MPI_Win_start

- MPI_Win_post

- MPI_Win_complete

- MPI_Win_wait