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 *compare_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.