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MPI_Win_fence(3OpenMPI)                                                              MPI_Win_fence(3OpenMPI)



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_NOPRE-CEDE) MPI_MODE_NOPRECEDE)
       CEDE) 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 syn-chronized synchronized
       chronized 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




Open MPI 1.2                                     March 2007                          MPI_Win_fence(3OpenMPI)