MPI_GET_ACCUMULATE(3)

📦

version 5.0.10 · 7 versions

✨ MPI_GET_ACCUMULATE ✨

okay bestie, welcome to the MPI_GET_ACCUMULATE(3) page 💖 this is the Open MPI manual, and we're gonna talk about the two icons of the day: MPI_Get_accumulate and MPI_Rget_accumulate. what do they do?? they combine the contents of the origin buffer with that of a target buffer and hand you back the target buffer value. it's giving read-and-write-in-one-move, no cap. 🎀

🌈 SYNTAX 🌈

💻 C Syntax

#include <mpi.h>

int MPI_Get_accumulate(const void *origin_addr, int origin_count,
    MPI_Datatype origin_datatype, void *result_addr,
    int result_count, MPI_Datatype result_datatype,
    int target_rank, MPI_Aint target_disp, int target_count,
    MPI_Datatype target_datatype, MPI_Op op, MPI_Win win)

int MPI_Rget_accumulate(const void *origin_addr, int origin_count,
    MPI_Datatype origin_datatype, void *result_addr,
    int result_count, MPI_Datatype result_datatype,
    int target_rank, MPI_Aint target_disp, int target_count,
    MPI_Datatype target_datatype, MPI_Op op, MPI_Win win,
    MPI_Request *request)

🧚 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_GET_ACCUMULATE(ORIGIN_ADDR, ORIGIN_COUNT, ORIGIN_DATATYPE, RESULT_ADDR,
        RESULT_COUNT, RESULT_DATATYPE, TARGET_RANK, TARGET_DISP, TARGET_COUNT,
        TARGET_DATATYPE, OP, WIN, IERROR)
    <type> ORIGIN_ADDR, RESULT_ADDR(*)
    INTEGER(KIND=MPI_ADDRESS_KIND) TARGET_DISP
    INTEGER ORIGIN_COUNT, ORIGIN_DATATYPE, TARGET_COUNT, TARGET_DATATYPE,
        TARGET_RANK, TARGET_COUNT, TARGET_DATATYPE, OP, WIN, IERROR

MPI_RGET_ACCUMULATE(ORIGIN_ADDR, ORIGIN_COUNT, ORIGIN_DATATYPE, RESULT_ADDR,
        RESULT_COUNT, RESULT_DATATYPE, TARGET_RANK, TARGET_DISP, TARGET_COUNT,
        TARGET_DATATYPE, OP, WIN, REQUEST, IERROR)
    <type> ORIGIN_ADDR, RESULT_ADDR(*)
    INTEGER(KIND=MPI_ADDRESS_KIND) TARGET_DISP
    INTEGER ORIGIN_COUNT, ORIGIN_DATATYPE, TARGET_COUNT, TARGET_DATATYPE,
        TARGET_RANK, TARGET_COUNT, TARGET_DATATYPE, OP, WIN, REQUEST, IERROR

🦋 Fortran 2008 Syntax

USE mpi_f08

MPI_Get_accumulate(origin_addr, origin_count, origin_datatype, result_addr,
        result_count, result_datatype, target_rank, target_disp,
        target_count, target_datatype, op, win, ierror)
    TYPE(*), DIMENSION(..), INTENT(IN) :: origin_addr
    TYPE(*), DIMENSION(..) :: result_addr
    INTEGER, INTENT(IN) :: origin_count, result_count, target_rank, target_count
    TYPE(MPI_Datatype), INTENT(IN) :: origin_datatype, target_datatype, result_datatype
    INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: target_dist
    TYPE(MPI_Op), INTENT(IN) :: op
    TYPE(MPI_Win), INTENT(IN) :: win
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

MPI_Rget_accumulate(origin_addr, origin_count, origin_datatype,
        result_addr, result_count, result_datatype, target_rank,
        target_disp, target_count, target_datatype, op, win, request,
        ierror)
    TYPE(*), DIMENSION(..), INTENT(IN) :: origin_addr
    TYPE(*), DIMENSION(..) :: result_addr
    INTEGER, INTENT(IN) :: origin_count, result_count, target_rank, target_count
    TYPE(MPI_Datatype), INTENT(IN) :: origin_datatype, target_datatype, result_datatype
    INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: target_dist
    TYPE(MPI_Op), INTENT(IN) :: op
    TYPE(MPI_Win), INTENT(IN) :: win
    TYPE(MPI_Request), INTENT(OUT) :: request
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

🎀 INPUT PARAMETERS 🎀

origin_addr — the initial address of the buffer (choice).
origin_count — how many entries are in that buffer (nonnegative integer).
origin_datatype — the data type of each buffer entry (handle).
result_addr — the initial address of the result buffer (choice).
result_count — number of entries in the result buffer (nonnegative) integer.
result_datatype — the data type of each result buffer entry (handle).
target_rank — the rank of the target (nonnegative integer).
target_disp — displacement from the start of the window to the beginning of the target buffer (nonnegative integer).
target_count — number of entries in the target buffer (nonnegative) integer.
target_datatype — the data type of each entry in the target buffer (handle).
op — the reduce operation (handle).
win — the window object (handle).

🫶 OUTPUT PARAMETER 🫶

MPI_Rget_accumulate — the RMA request.
ierror — Fortran only: error status (integer).

💖 DESCRIPTION 💖

so MPI_Get_accumulate is a one-sided MPI communication function, aka it does its own thing on the wire without needing the target to show up to the group chat 🫶. what it does is add the contents of the origin buffer (as defined by origin_addr, origin_count, and origin_datatype) to the buffer specified by target_count and target_datatype, at offset target_disp, in the target window specified by target_rank and win, using the operation op. and then — this is the iconic part ✨ — MPI_Get_accumulate returns in the result buffer result_addr the contents of the target buffer before the accumulation happened. it's giving receipts, bestie.

Any of the predefined operations for MPI_Reduce, as well as MPI_NO_OP, can be used. User-defined functions cannot be used. like, at all. for example, if op is MPI_SUM, each element of the origin buffer is added to the corresponding element in the target, replacing the former value in the target. math but make it flirty 💅.

Each datatype argument must be a predefined data type or a derived data type, where all basic components are of the same predefined data type. Both datatype arguments must be constructed from the same predefined data type. The operation op applies to elements of that predefined data type. The target_datatype argument must not specify overlapping entries, and the target buffer must fit in the target window. no overlapping, no sneaky window overflow, we don't do that here 🙈.

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. out with the old, in with the new, queen 👑.

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. read-only energy, and honestly? same. 🌸

MPI_Rget_accumulate is similar to MPI_Get_accumulate, except that it allocates a communication request object and associates it with the request handle (the argument request) that can be used to wait or test for completion. The completion of an MPI_Rget_accumulate operation indicates that the data is available in the result buffer and the origin buffer is free to be updated. It does not indicate that the operation has been completed at the target window. like, the origin side is done, but do not assume the target side is — fr fr, read that twice. 📌

👑 NOTES 👑

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. so if you're doing that specific little dance, MPI_Fetch_and_op is your glowed-up shortcut ⭐.

MPI_Get is a special case of MPI_Get_accumulate, with the operation MPI_NO_OP. Note, however, that MPI_Get and MPI_Get_accumulate have different constraints on concurrent updates. they're cousins, not twins, iykyk 😭.

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_Get_accumulate function. that one's on you bestie, alignment is a you problem 💀.

💀 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:

MPI_ERRORS_ARE_FATAL — Causes the program to abort all connected MPI processes. 💀
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.
MPI_ERRORS_RETURN — Returns an error code to the application.

MPI applications can also implement their own error handlers by calling:

MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
MPI_File_create_errhandler then MPI_File_set_errhandler
MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
MPI_Win_create_errhandler then MPI_Win_set_errhandler

Note that MPI does not guarantee that an MPI program can continue past an error. not me finding out the hard way 😭.

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.

📜 Copyright 📜

2003-2026, The Open MPI Community

and that's the whole page bestie, you ate it 💅✨ this was the MPI_GET_ACCUMULATE(3) manual from Open MPI, datestamped Sep 10, 2026 🎀 go forth and accumulate, but like, correctly 🦋💖

📦 where this page comes from

ubuntu stonking: openmpi-doc 5.0.10-6 · other
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-11-03: a language model's rewrite of the original, under its terms