MPI_Compare_and_swap(3)

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)
USE MPI
! or the older form: 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

Fortran 2008 Syntax
USE mpi_f08
MPI_Compare_and_swap(origin_addr, compare_addr, result_addr, datatype,
		target_rank, target_disp, win, ierror)
	TYPE(*), DIMENSION(..), INTENT(IN) :: origin_addr, compare_addr
	TYPE(*), DIMENSION(..) :: result_addr
	TYPE(MPI_Datatype), INTENT(IN) :: datatype
	INTEGER, INTENT(IN) :: target_rank
	INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: target_disp
	TYPE(MPI_Win), INTENT(IN) :: win
	INTEGER, OPTIONAL, INTENT(OUT) :: 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.