MPI_Fetch_and_op(3) Combines the contents of the origin buffer with that of a target buffer and returns the target buffer value.

SYNTAX

C Syntax

#include <mpi.h>
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)

Fortran Syntax (see FORTRAN 77 NOTES)

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

INPUT PARAMETERS

origin_addr
Initial address of 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).
op
Reduce operation (handle).
win
Window object (handle).

OUTPUT PARAMETER

IERROR
Fortran only: Error status (integer).

DESCRIPTION

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 contents of the target buffer before the accumulation.

The origin and result buffers (origin_addr and result_addr) must be disjoint. Any of the predefined operations for MPI_Rreduce, 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. The operation is executed atomically.

A new predefined operation, MPI_REPLACE, is defined. It corresponds to the associative function f(a, b) =b; that is, the current value in the target memory is replaced by the value supplied by the origin.

A new predefined operation, MPI_NO_OP, is defined. It corresponds to the assiciative function f(a, b) = a; that is the current value in the target memory is returned in the result buffer at the origin and no operation is performed on the target buffer.

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_Fetch_and_op 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.

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