MPI_FETCH_AND_OP(3) Open MPI MPI_FETCH_AND_OP(3)
MPI_Fetch_and_op -- 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
o origin_addr: Initial address of buffer (choice).
o result_addr: Initial address of result buffer (choice).
o datatype: Data type of the entry in origin, result, and target
buffers (handle).
o target_rank: Rank of target (nonnegative integer).
o target_disp: Displacement from start of window to beginning of target
buffer (nonnegative integer).
o op: Reduce operation (handle).
o win: Window object (handle).
OUTPUT PARAMETER
o 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 MPI_Fetch_and_op function.
ERRORS
Almost all MPI routines return an error value; C routines as the return
result of the function and Fortran routines in the last argument.
Before the error value is returned, the current MPI error handler
associated with the communication object (e.g., communicator, window,
file) is called. If no communication object is associated with the MPI
call, then the call is considered attached to MPI_COMM_SELF and will
call the associated MPI error handler. When MPI_COMM_SELF is not
initialized (i.e., before MPI_Init/MPI_Init_thread, after MPI_Finalize,
or when using the Sessions Model exclusively) the error raises the
initial error handler. The initial error handler can be changed by
calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World
model, or the mpi_initial_errhandler CLI argument to mpiexec or info
key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. If no other appropriate
error handler has been set, then the MPI_ERRORS_RETURN error handler is
called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is
called for all other MPI functions.
Open MPI includes three predefined error handlers that can be used:
o MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI
processes.
o MPI_ERRORS_ABORT An error handler that can be invoked on a
communicator, window, file, or session. When called on a
communicator, it acts as if MPI_Abort was called on that
communicator. If called on a window or file, acts as if MPI_Abort was
called on a communicator containing the group of processes in the
corresponding window or file. If called on a session, aborts only the
local process.
o MPI_ERRORS_RETURN Returns an error code to the application.
MPI applications can also implement their own error handlers by
calling:
o MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
o MPI_File_create_errhandler then MPI_File_set_errhandler
o MPI_Session_create_errhandler then MPI_Session_set_errhandler or at
MPI_Session_init
o MPI_Win_create_errhandler then MPI_Win_set_errhandler
Note that MPI does not guarantee that an MPI program can continue past
an error.
See the MPI man page for a full list of MPI error codes.
See the Error Handling section of the MPI-3.1 standard for more
information.
SEE ALSO:
o MPI_Get_accumulate
o MPI_Reduce
COPYRIGHT
2003-2025, The Open MPI Community
February 14, 2025 MPI_FETCH_AND_OP(3)