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