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.

Input Parameters

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 integer)
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.

Notes for Fortran

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