NAME

       MPI_Compare_and_swap - Perform RMA compare-and-swap

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Compare_and_swap(const void *origin_addr, const void *compar_addr,
            void *result_addr, MPI_Datatype datatype, int target_rank,
            MPI_Aint target_disp, MPI_Win win)

Fortran Syntax (see FORTRAN 77 NOTES)

       INCLUDE 'mpif.h'
       MPI_COMPARE_AND_SWAP(ORIGIN_ADDR, COMPARE_ADDR, RESULT_ADDR, DATATYPE, TARGET_RANK,
            TARGET_DISP, WIN, IERROR)
            <type> ORIGIN_ADDR, COMPARE_ADDR, RESULT_ADDR(*)
            INTEGER(KIND=MPI_ADDRESS_KIND) TARGET_DISP
            INTEGER DATATYPE, TARGET_RANK, WIN, IERROR

INPUT PARAMETERS

       origin_addr
                 Initial address of buffer (choice).

       compare_addr
                 Initial address of compare buffer (choice).

       result_addr
                 Initial address of result buffer (choice).

       datatype  Data type of the entry in origin, result, and target buffers (handle).

       target_rank
                 Rank of target (nonnegative integer).

       target_disp
                 Displacement  from  start  of  window to beginning of target buffer (nonnegative
                 integer).

       win       Window object (handle).

OUTPUT PARAMETER

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       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. 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 MPI-3 § 5.9.2 on page 176.

       The origin and result buffers (origin_addr and result_addr) must be disjoint.

FORTRAN 77 NOTES

       The MPI standard prescribes portable Fortran syntax for the TARGET_DISP argument only  for
       Fortran 90.  FORTRAN 77 users may use the non-portable syntax

            INTEGER*MPI_ADDRESS_KIND TARGET_DISP

       where  MPI_ADDRESS_KIND  is  a  constant  defined  in  mpif.h  and gives the length of the
       declared integer in bytes.

NOTES

       It is the user's responsibility to guarantee that, when using  the  accumulate  functions,
       the  target displacement argument is such that accesses to the window are properly aligned
       according to the data type arguments in the call to the MPI_Compare_and_swap function.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran routines in the last argument.

       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.