SHMEM_LONG_ADD(3)

💖 SHMEM_LONG_ADD(3) — the Open MPI girlies' atomic add moment 💖

okay bestie, welcome to the group chat 🫶 today's topic: shmem_int_add, shmem_int4_add, shmem_int8_add, shmem_long_add, and shmem_longlong_add — yes that one is literally shmem_longlong_add <#shmem-longlong-add>(3) in the docs, and yes, shmem_int_add <#shmem-int-add>(3) too, anchors and all, we do not edit the sacred texts ✨

anyway. these five icons perform an atomic add operation. that's the whole vibe: add, but make it un-interruptible 💅

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🌸 SYNOPSIS 🌸

C or C++:

#include <mpp/shmem.h>

void shmem_int_add(int *target, int value, int pe)
void shmem_long_add(long *target, long value, int pe)
void shmem_longlong_add(long long *target, long long value,
  int pe)

Fortran:

include 'mpp/shmem.h'

INTEGER pe

CALL SHMEM_INT4_ADD(target, value, pe)
CALL SHMEM_INT8_ADD(target, value, pe)

note the Fortran include 'mpp/shmem.h' — yes it's literally mpp/shmem.h both times, no I will not be explaining that, that's just how it is 🙈

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✨ DESCRIPTION ✨

so the atomic add routines add value to the data at address target on PE pe. and here's the slay part: the operation completes without the possibility of another process updating target between the time of the fetch and the update. no race conditions, no ✨drama✨, just atomicity. main character energy fr fr 🔥

the arguments, bestie:

• target — the remotely accessible integer data object that's gonna get updated on the remote PE. if you're in C/C++, the type of target should match whatever the SYNOPSIS section implies (it's giving match it exactly, no cap). if you're on a Fortran compiler, it has to be type integer with an element size of 4 bytes for SHMEM_INT4_ADD and 8 bytes for SHMEM_INT8_ADD. 👑
• value — the value being atomically added to target. C/C++ girlies: match the type implied in SYNOPSIS. Fortran girlies: it must be type integer with an element size of target. 🎀
• pe — an integer that says which PE number target is getting updated on. Fortran besties, heads up: it must be a default integer value. 🦋

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💜 NOTES 💜

the term remotely accessible is defined in intro_shmem(3) — go read it, it's required lore iykyk 📖

See also: intro_shmem(3) shmem_cache(3)

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and that's the whole page, periodt 💅

Copyright — 2003-2026, The Open MPI Community 🫶

signing off from Sep 10, 2026 — SHMEM_LONG_ADD(3), Open MPI, that's the tea 🍓🧚💜