Perform one-sided read-modify-write.


int MPI_Fetch_and_op(const void *origin_addr, void *result_addr,
        MPI_Datatype datatype, int target_rank, MPI_Aint target_disp,
        MPI_Op op, MPI_Win win)

Accumulate one element of type datatype from the origin buffer (origin_addr) to the buffer at offset target_disp, in the target window specified by target_rank and win, using the operation op and return in the result buffer result_addr the content of the target buffer before the accumulation.

Input Parameters

initial address of 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)
reduce operation (handle)
window object (handle)


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

The generic functionality of MPI_Get_accumulate might limit the performance of fetch-and-increment or fetch-and-add calls that might be supported by special hardware operations. MPI_Fetch_and_op thus allows for a fast implementation of a commonly used subset of the functionality of MPI_Get_accumulate.

The origin and result buffers (origin_addr and result_addr) must be disjoint. Any of the predefined operations for MPI_Reduce, as well as MPI_NO_OP or MPI_REPLACE, can be specified as op; user-defined functions cannot be used. The datatype argument must be a predefined datatype.

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

See Also MPI_Get_accumulate