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

       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

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

4.1.6                                             Sep 30, 2023                                  MPI_Win_fence(3)