Ubuntu Manpage: MPI_Win_fence - Synchronizes RMA calls on a window.

Provided by: openmpi-doc_4.1.4-3ubuntu2_all

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.