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MPI_Fetch_and_op.3.rst

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MPI_Fetch_and_op

:ref:`MPI_Fetch_and_op` |mdash| 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

USE MPI
! or the older form: 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

Fortran 2008 Syntax

USE mpi_f08
MPI_Fetch_and_op(origin_addr, result_addr, datatype, target_rank,
             target_disp, op, win, ierror)
     TYPE(*), DIMENSION(..), INTENT(IN) :: origin_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_Op), INTENET(IN) :: op
     TYPE(MPI_Win), INTENT(IN) :: win
     INTEGER, OPTIONAL, INTENT(OUT) :: 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.

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 :ref:`MPI_Fetch_and_op` function.

ERRORS

.. seealso::
   * :ref:`MPI_Get_accumulate`
   * :ref:`MPI_Reduce`