MPI_Win_fence(3)                   Open MPI                   MPI_Win_fence(3)



NAME
       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
       INCLUDE 'mpif.h'
       MPI_WIN_FENCE(ASSERT, WIN, IERROR)
            INTEGER ASSERT, WIN, IERROR


C++ Syntax
       #include <mpi.h>
       void MPI::Win::Fence(int assert) const


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.

       A fence call usually entails a barrier synchronization: a process
       completes a call to MPI_Win_fence only after all other processes in the
       group have entered their matching call. However, a call to
       MPI_Win_fence that is known not to end any epoch (in particular, a call
       with assert = MPI_MODE_NOPRECEDE) does not necessarily act as a
       barrier.


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 value
       of the function and Fortran routines in the last argument. C++
       functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before the error value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed with
       MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
       may be used to cause error values to be returned. Note that MPI does
       not guarantee that an MPI program can continue past an error.


SEE ALSO
       MPI_Win_create MPI_Win_start MPI_Win_post MPI_Win_complete MPI_Win_wait




1.4.1                            Jan 14, 2010                 MPI_Win_fence(3)
