SHMEM_LONGLONG_CSWAP(3)

📦

version 5.0.10 · 4 versions

💅 SHMEM_LONGLONG_CSWAP — it's giving Open MPI

okay so bestie, gather round 🫶 this is the whole lil family of conditional swap routines from Open MPI, and they are honestly the main characters of atomic operations. You've got shmem_int_cswap(3), shmem_int4_cswap(3), shmem_int8_cswap(3), shmem_long_cswap(3), and shmem_longlong_cswap(3) — and every single one of them performs an atomic conditional swap to a remote data object. no cap. ✨

✨ 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)

💖 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. like, it's one single move, no splitting, no drama. 👑

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.

yes bestie, target, value and pe show up twice up there. that's just how the page is built. we don't edit the vibes, we honor them. 💅

📝 NOTES 📝

The term remotely accessible is defined in intro_shmem(3). go read her, she's the blueprint. 🎀

⭐ RETURN VALUES ⭐

The contents that had been in the target data object on the remote PE prior to the conditional swap. it's giving "here's what you missed, babe". 🙈

🔥 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. honestly? iconic race-condition energy. 🏁

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());
}