SHMEM_LONG_SWAP(3)

🌸 NAME 🌸

shmem_double_swap(3), shmem_float_swap(3), shmem_int_swap(3), shmem_long_swap(3), shmem_swap(3), shmem_int4_swap(3), shmem_int8_swap(3), shmem_real4_swap(3), shmem_real8_swap(3), shmem_longlong_swap(3) — bestie, these all do one iconic thing: perform an atomic swap to a remote data object 💖

This is the <cyan>shmem_long_swap(3)</cyan> page from the Open MPI manual, and she contains multitudes (a whole lil family of swap functions, actually). Let's get into it ✨

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🦋 SYNOPSIS 🦋

okay so, C or C++ girlies:

#include <mpp/shmem.h>

double shmem_double_swap(double *target, double value,
  int pe)

float shmem_float_swap(float *target, float value, int pe)

int shmem_int_swap(int *target, int value, int pe)

long shmem_long_swap(long *target, long value, int pe)

long long shmem_longlong_swap(long long *target,
  long long value, int pe)

long shmem_swap(long *target, long value, int pe)

and for the Fortran besties:

INCLUDE "mpp/shmem.fh"

INTEGER pe

INTEGER SHMEM_SWAP
ires = SHMEM_SWAP(target, value, pe)

INTEGER(KIND=4) SHMEM_INT4_SWAP
ires = SHMEM_INT4_SWAP(target, value, pe)

INTEGER(KIND=8) SHMEM_INT8_SWAP
ires = SHMEM_INT8_SWAP(target, value, pe)

REAL(KIND=4) SHMEM_REAL4_SWAP
res = SHMEM_REAL4_SWAP(target, value, pe)

REAL(KIND=8) SHMEM_REAL8_SWAP
res = SHMEM_REAL8_SWAP(target, value, pe)

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👑 DESCRIPTION 👑

The atomic swap routines write value to address target on PE pe, and return the previous contents of target in one atomic operation 🌈 Like, it's all one move, no in-between, no half-swapped mess. Periodt.

Here's the cast of arguments, and yes they each have main character energy 💅

• target — the remotely accessible integer data object being updated on the remote PE. If you're in C/C++ land, the type of target should match whatever the SYNOPSIS says it is (no mixing and matching, iykyk). If you're doing Fortran, it's gotta be one of these types:
  • SHMEM_SWAP: Integer of default kind
  • SHMEM_INT4_SWAP: 4-byte integer
  • SHMEM_INT8_SWAP: 8-byte integer
  • SHMEM_REAL4_SWAP: 4-byte real
  • SHMEM_REAL8_SWAP: 8-byte real
• value — the value getting atomically written to the remote PE. She is the same type as target, no cap 🫶
• pe — an integer that says which PE number target is getting updated on. In Fortran it must be a default integer value, fr fr.

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📝 NOTES 📝

The term remotely accessible is defined over in intro_shmem(3). Go peek if you need the full tea 🍵

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💖 RETURN VALUES 💖

Whatever was sitting at the target address on the remote PE before the swap happened? Yeah, that's what you get back. The old value is returned to you, bestie — nothing gets lost, everything gets traded 😭🔥

See also: intro_shmem(3)

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🎀 Copyright 🎀

2003-2026, The Open MPI Community — they've been holding it down since 2003, iconic behavior honestly 👑

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okay that's the whole page!! this was SHMEM_LONG_SWAP(3) from Open MPI, last touched Sep 10, 2026 — go forth and swap atomically, you've got this 💜🧚✨