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       MPI_Win_start -  Start an RMA access epoch for MPI


       int MPI_Win_start(MPI_Group group, int assert, MPI_Win win)


       group  - group of target processes (handle)
       assert - Used to optimize this call; zero may be used as a default.  See notes. (integer)
       win    - window object (handle)


       The  assert  argument  is  used  to  indicate  special  conditions  for  the fence that an
       implementation may use to optimize the MPI_Win_start operation.  The value zero is  always
       correct.   Other  assertion  values  may  be or'ed together.  Assertions tha are valid for
       MPI_Win_start are:

              - the matching calls to MPI_WIN_POST have already completed on all target processes
              when  the  call to MPI_WIN_START is made.  The nocheck option can be specified in a
              start call if and only if it is specified in  each  matching  post  call.  This  is
              similar  to  the  optimization  of  ready-send  that  may save a handshake when the
              handshake is implicit in the code. (However, ready-send is  matched  by  a  regular
              receive, whereas both start and post must specify the nocheck option.)


       This  routine is thread-safe.  This means that this routine may be safely used by multiple
       threads without the need for any user-provided thread locks.  However, the routine is  not
       interrupt  safe.   Typically, this is due to the use of memory allocation routines such as
       malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.


       All MPI routines in Fortran (except for MPI_WTIME  and  MPI_WTICK  )  have  an  additional
       argument  ierr  at  the  end  of  the  argument list.  ierr is an integer and has the same
       meaning as the  return  value  of  the  routine  in  C.   In  Fortran,  MPI  routines  are
       subroutines, and are invoked with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.


       All  MPI  routines  (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as
       the value of the function and Fortran routines in the last argument.  Before the value  is
       returned,  the current MPI error handler is called.  By default, this error handler aborts
       the MPI  job.   The  error  handler  may  be  changed  with  MPI_Comm_set_errhandler  (for
       communicators),  MPI_File_set_errhandler  (for files), and MPI_Win_set_errhandler (for RMA
       windows).  The MPI-1 routine MPI_Errhandler_set may be used but  its  use  is  deprecated.
       The  predefined  error  handler  MPI_ERRORS_RETURN may be used to cause error values to be
       returned.  Note that MPI does not guarentee that an  MPI  program  can  continue  past  an
       error; however, MPI implementations will attempt to continue whenever possible.

              - No error; MPI routine completed successfully.
              - Invalid MPI window object
              - Other error; use MPI_Error_string to get more information about this error code.

                                            11/21/2018                           MPI_Win_start(3)