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       MPI_Compare_and_swap -  Perform one-sided atomic compare-and-swap.


       int MPI_Compare_and_swap(const void *origin_addr, const void *compare_addr,
               void *result_addr, MPI_Datatype datatype, int target_rank,
               MPI_Aint target_disp, MPI_Win win)

       This  function  compares  one  element of type datatype in the compare buffer compare_addr
       with the buffer at offset target_disp in the target window specified  by  target_rank  and
       win  and  replaces the value at the target with the value in the origin buffer origin_addr
       if the compare buffer and the target buffer are  identical.  The  original  value  at  the
       target is returned in the buffer result_addr.


              - initial address of buffer (choice)
              - initial address of compare buffer (choice)
              - initial address of result buffer (choice)
              - datatype of the entry in origin, result, and target buffers (handle)
              - rank of target (nonnegative integer)
              -  displacement  from  start  of window to beginning of target buffer (non-negative
       win    - window object (handle)


       This operation is atomic with respect to other "accumulate" operations.

       The parameter datatype must belong to  one  of  the  following  categories  of  predefined
       datatypes: C integer, Fortran integer, Logical, Multi-language types, or Byte as specified
       in Section 5.9.2 on page 176. The origin and result buffers (origin_addr and  result_addr)
       must be disjoint.


       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 argument.  Some argument is invalid and is not identified by  a  specific
              error class (e.g., MPI_ERR_RANK ).
              - Invalid count argument.  Count arguments must be non-negative; a count of zero is
              often valid.
              - Invalid operation.  MPI operations (objects of type MPI_Op ) must either  be  one
              of the predefined operations (e.g., MPI_SUM ) or created with MPI_Op_create .

              -  Invalid  source or destination rank.  Ranks must be between zero and the size of
              the  communicator  minus  one;  ranks  in  a  receive  (  MPI_Recv  ,  MPI_Irecv  ,
              MPI_Sendrecv , etc.) may also be MPI_ANY_SOURCE .

              -  Invalid datatype argument.  Additionally, this error can occur if an uncommitted
              MPI_Datatype (see MPI_Type_commit ) is used in a communication call.
              - Invalid MPI window object

                                            11/9/2015                     MPI_Compare_and_swap(3)