SHMEM_INT_CSWAP(3)

💖 SHMEM_INT_CSWAP(3) 💖

okay bestie, gather round, because we're talking about the conditional swap girlies from Open MPI — that's shmem_int_cswap(3), shmem_int4_cswap(3), shmem_int8_cswap(3), shmem_long_cswap(3), and shmem_longlong_cswap(3). they all do the same iconic thing: an atomic conditional swap on a remote data object. no cap. 🦋

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✨ NAME ✨

shmem_int_cswap(3), shmem_int4_cswap(3), shmem_int8_cswap(3), shmem_long_cswap(3), shmem_longlong_cswap(3) — Performs an atomic conditional swap to a remote data object

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🌸 SYNOPSIS 🌸

C or C++:

#include <mpp/shmem.h>

int shmem_int_cswap(int *target, int cond, int value, int pe)

long shmem_long_cswap(long *target, long cond, long value,
  int pe)

long long shmem_longlong_cswap(longlong *target,
  longlong cond, longlong value, int pe)

Fortran:

INCLUDE "mpp/shmem.fh"

INTEGER pe

INTEGER(KIND=4) SHMEM_INT4_CSWAP
ires = SHMEM_INT4_CSWAP(target, cond, value, pe)

INTEGER(KIND=8) SHMEM_INT8_CSWAP
ires = SHMEM_INT8_CSWAP(target, cond, value, pe)

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👑 DESCRIPTION 👑

The conditional swap routines conditionally update a target data object on an arbitrary processing element (PE) and return the prior contents of the data object in one atomic operation. it's giving "one shot, no take-backs" energy, fr fr. 💅

The arguments are as follows:

• target — The remotely accessible integer data object to be updated on the remote PE. If you are using C/C++, the type of target should match that implied in the SYNOPSIS section. If you are using the Fortran compiler, it must be of type integer with an element size of 4 bytes for SHMEM_INT4_ADD and 8 bytes for SHMEM_INT8_ADD.
• value — The value to be atomically added to target. If you are using C/C++, the type of value should match that implied in the SYNOPSIS section. If you are using Fortran, it must be of type integer with an element size of target.
• pe — An integer that indicates the PE number upon which target is to be updated. If you are using Fortran, it must be a default integer value.
• target — The remotely accessible integer data object to be updated on the remote PE. If you are using C/C++, the data type of target should match that implied in the SYNOPSIS section. If you are using Fortran, it must be of the following type:
  • SHMEM_INT4_CSWAP: 4-byte integer
  • SHMEM_INT8_CSWAP: 8-byte integer
• cond — cond is compared to the remote target value. If cond and the remote target are equal, then value is swapped into the remote target. Otherwise, the remote target is unchanged. In either case, the old value of the remote target is returned as the function return value. cond must be of the same data type as target.
• value — The value to be atomically written to the remote PE. value must be the same data type as target.
• pe — An integer that indicates the PE number upon which target is to be updated. If you are using Fortran, 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, i'll wait 🫶

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⭐ RETURN VALUES ⭐

The contents that had been in the target data object on the remote PE prior to the conditional swap. literally the old vibes, handed back to you. 😭

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🌈 EXAMPLES 🌈

The following call ensures that the first PE to execute the conditional swap will successfully write its PE number to race_winner on PE 0.

main()
{
  static int race_winner = -1;
  int oldval;

  shmem_init();
  oldval = shmem_int_cswap(&race_winner, -1, shmem_my_pe(), 0);
  if (oldval == -1)
    printf("pe %d was first\n",shmem_my_pe());
}

See also: intro_shmem(3) shmem_cache(3) shmem_swap(3)

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🔥 SEE ALSO 🔥

• intro_shmem(3)
• shmem_cache(3)
• shmem_swap(3)

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tiny reminder bestie: the whole "remotely accessible" thing has a whole definition over in intro_shmem(3), so if that word is doing heavy lifting in your brain rn, that's where it lives.

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💜 Copyright 💜

2003-2026, The Open MPI Community

okay that's the whole page, mwah 💋 this was SHMEM_INT_CSWAP(3) from the Open MPI girlies, dropped Sep 10, 2026, copyright 2003-2026, The Open MPI Community — stay atomic, stay slay, periodt. ✨🎀🦋💅