--- name: "MPI_Win_fence" section: "3" platform: "linux" package: "openmpi" version: "5.0.11-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/MPI_Win_fence" --- # MPI\_Win\_fence(3) *MPI\_Win\_fence* — Synchronizes RMA calls on a window. ## SYNTAX ### C Syntax ``` #include 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 accumulate 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\_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* ## COPYRIGHT 2003-2026, The Open MPI Community