MPI_Get_accumulate(3)

👑 MPI_Get_accumulate(3) — the MPI manual, bestie edition

okay so this one lives in the MPI manual section (yeah, MPI_Get_accumulate(3), that's the whole vibe) and it is SO much. it's an atomic, one-sided read-and-accumulate operation. read. accumulate. atomically. one-sided. the way that it does ALL of that without even asking the target for permission?? iconic behavior, no cap. 💅

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✨ NAME ✨

MPI_Get_accumulate — perform an atomic, one-sided read-and-accumulate operation 🦋

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🌸 SYNOPSIS 🌸

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

two versions, because of course there are — the regular one and the _c one where the counts get to be MPI_Count instead of plain int. slay 💖

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💜 INPUT PARAMETERS 💜

• origin_addr — initial address of buffer (choice)
• origin_count — number of entries in origin buffer (non-negative integer)
• origin_datatype — datatype of each entry in origin buffer (handle)
• result_count — number of entries in result buffer (non-negative integer)
• result_datatype — datatype of each entry in result buffer (handle)
• target_rank — rank of target (non-negative integer)
• target_disp — displacement from start of window to beginning of target buffer (non-negative integer)
• target_count — number of entries in target buffer (non-negative integer)
• target_datatype — datatype of each entry in target buffer (handle)
• op — reduce operation (handle)
• win — window object (handle)

quick lil note bestie: result_addr is NOT in this list, keep scrolling 💀

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🎀 OUTPUT PARAMETERS 🎀

• result_addr — initial address of result buffer (choice)

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🔥 NOTES 🔥

this operation is atomic with respect to other "accumulate" operations. periodt.

the get and accumulate steps are executed atomically for each basic element in the datatype (see MPI 3.0 Section 11.7 for details, iykyk). and the predefined operation MPI_REPLACE provides fetch-and-set behavior. cute.

the origin and result buffers (origin_addr and result_addr) must be disjoint. not overlapping. not adjacent-and-lying-about-it. disjoint. 🫶

each datatype argument must be a predefined datatype or a derived datatype where all basic components are of the same predefined datatype. all datatype arguments must be constructed from the same predefined datatype. the operation op applies to elements of that predefined type. target_datatype must not specify overlapping entries, and the target buffer must fit in the target window or in attached memory in a dynamic window. no squeezing, bestie, it has to fit. 💅

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. sorry to the girlies who wanted to write their own function, it's giving not-allowed. 😭

a new predefined operation, MPI_NO_OP, is defined. it corresponds to the associative function f (a, b) = a; i.e., 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. MPI_NO_OP can be used only in MPI_Get_accumulate, MPI_Rget_accumulate, and MPI_Fetch_and_op. MPI_NO_OP cannot be used in MPI_Accumulate, MPI_Raccumulate, or collective reduction operations, such as MPI_Reduce and others. 🚫

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🧚 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 they are invoked with the call statement. (yes, call. we love her. 💜)

all MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran. so if you were out here typing <blue>MPI_Datatype</blue> in your .f90 file… bestie no. 💀

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⭐ ERRORS ⭐

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. like, whole program, gone, done. 🪦

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, so like, don't. 🙈

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; however, MPI implementations will attempt to continue whenever possible. she's trying her best, okay?? 🥺

• MPI_SUCCESS — No error; MPI routine completed successfully. slay ✅
• MPI_ERR_BUFFER — Invalid buffer pointer. Usually a null buffer where one is not valid.
• MPI_ERR_COUNT — Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
• MPI_ERR_DISP — (okay so the original page literally leaves this one blank. no description. nothing. i'm not making anything up, i'm just reporting the silence 💀)
• MPI_ERR_RANK — 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.
• MPI_ERR_TYPE — Invalid datatype argument. Additionally, this error can occur if an uncommitted MPI_Datatype (see MPI_Type_commit) is used in a communication call.
• MPI_ERR_WIN — Invalid MPI window object
• MPI_ERR_OTHER — Other error; use MPI_Error_string to get more information about this error code.

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🦋 SEE ALSO 🦋

MPI_Rget_accumulate MPI_Fetch_and_op

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okay that's the whole page, bestie, you're welcome 💖 go forth and accumulate atomically. this was the MPI manual, MPI_Get_accumulate(3), and the footer said 4/10/2026 — so like, shoutout to that date, and shoutout to you for reading all the way to the end. main character energy fr fr. 🌈✨👑