SHMEM_LONGLONG_WAIT_UNTIL(3)

📦
version 5.0.10 · 4 versions
, in ubuntu stonking

🎀 NAME 🎀

okay so this is the page for SHMEM_LONGLONG_WAIT_UNTIL(3) from the Open MPI manual, and bestie, it's literally the whole family of "wait for a variable on the local processing element (PE) to change" functions, gathered in one place:

and their whole entire job is: waits for a variable on the local processing element (PE) to change. periodt. 💅

✨ SYNOPSIS ✨

C or C++:

#include <mpp/shmem.h>

void shmem_int_wait(volatile int *var, int value)

void shmem_int_wait_until(volatile int *var, int cond, int value)

void shmem_long_wait(volatile long *var, long value)

void shmem_long_wait_until(volatile long *var, int cond, long value)

void shmem_longlong_wait(volatile long long *var, long long value)

void shmem_longlong_wait_until(volatile long long *var, int cond,
  long long value)

void shmem_short_wait(volatile short *var, short value)

void shmem_short_wait_until(volatile short *var, int cond,
  short value)

void shmem_wait(volatile long *ivar, long cmp_value)

void shmem_wait_until(volatile long *ivar, int cmp, long value)

Fortran:

INCLUDE "mpp/shmem.fh"

CALL SHMEM_INT4_WAIT(ivar, cmp_value)

CALL SHMEM_INT4_WAIT_UNTIL(ivar, cmp, cmp_value)

CALL SHMEM_INT8_WAIT(ivar, cmp_value)

CALL SHMEM_INT8_WAIT_UNTIL(ivar, cmp, cmp_value)

CALL SHMEM_WAIT(ivar, cmp_value)

CALL SHMEM_WAIT_UNTIL(ivar, cmp, cmp_value)

💖 DESCRIPTION 💖

so shmem_wait and shmem_wait_until are out here just waiting for ivar to get changed by a remote write or an atomic swap issued by a different processor. no cap. these routines are your go-to for point-to-point directed synchronization, iykyk.

a call to shmem_wait does not return until some other processor writes a value into ivar — on the waiting processor — that is not equal to cmp_value. 🫶

a call to shmem_wait_until does not return until some other processor changes ivar so that it satisfies the condition implied by cmp and cmp_value.

this mechanism is so useful when one processor needs to tell another processor that it has completed some action. it's giving "hey bestie, I'm done, you can go now" energy. 💌

The arguments are as follows:

  • target — the remotely accessible integer data object to be updated on the remote PE. if you're in C/C++, the type of target should match what's implied in the SYNOPSIS section. if you're 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're in C/C++, the type of value should match what's implied in the SYNOPSIS section. if you're in 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're in Fortran, it must be a default integer value.
  • ivar — a remotely accessible integer variable that is being updated by another PE. if you're in C/C++, the type of ivar should match what's implied in the SYNOPSIS section. if you're in Fortran, ivar must be a specific sized integer type based on which function you're calling, like so:
    • shmem_wait, shmem_wait_until: default INTEGER
    • shmem_int4_wait, shmem_int4_wait_until: INTEGER*4
    • shmem_int8_wait, shmem_int8_wait_until: INTEGER*8
  • cmp — the compare operator that compares ivar with cmp_value. cmp must be of type integer. if you're in Fortran, it must be of default kind. if you're in C/C++, the type of cmp should match what's implied in the SYNOPSIS section. these cmp values are supported, bestie, memorize them:
    • SHMEM_CMP_EQ — Equal
    • SHMEM_CMP_NE — Not equal
    • SHMEM_CMP_GT — Greater than
    • SHMEM_CMP_LE — Less than or equal to
    • SHMEM_CMP_LT — Less than
    • SHMEM_CMP_GE — Greater than or equal to
  • cmp_value — cmp_value must be of type integer. if you're in C/C++, the type of cmp_value should match what's implied in the SYNOPSIS section. if you're in Fortran, cmp_value must be an integer of the same size and kind as ivar. the shmem_wait routines return when ivar is no longer equal to cmp_value. the shmem_wait_until routines return when the compare condition is true. and that compare condition? it's defined by the ivar argument compared with cmp_value using the comparison operator, cmp. slay. 💅

🌈 EXAMPLES 🌈

Example 1: the following call returns when variable ivar is not equal to 100:

INTEGER*8 IVAR

CALL SHMEM_INT8_WAIT(IVAR, INT8(100))

Example 2: the following call to SHMEM_INT8_WAIT_UNTIL is equivalent to the call to SHMEM_INT8_WAIT in example 1:

INTEGER*8 IVAR

CALL SHMEM_INT8_WAIT_UNTIL(IVAR, SHMEM_CMP_NE, INT8(100))

Example 3: the following C/C++ call waits until the sign bit in ivar is set by a transfer from a remote PE:

int ivar;

shmem_int_wait_until(&ivar, SHMEM_CMP_LT, 0);

Example 4: the following Fortran example is in the context of a subroutine:

SUBROUTINE EXAMPLE()
  INTEGER FLAG_VAR
  COMMON/FLAG/FLAG_VAR
  . . .
  FLAG_VAR = FLAG_VALUE ! initialize the event variable
  . . .
  IF (FLAG_VAR .EQ. FLAG_VALUE) THEN
    CALL SHMEM_WAIT(FLAG_VAR, FLAG_VALUE)
  ENDIF
  FLAG_VAR = FLAG_VALUE ! reset the event variable for next time
  . . .
END

🦋 See also 🦋

intro_shmem(3) shmem_put(3)

bestie if you're stuck on the whole PE/variable-to-change situation, go read these next — they're the ✨iconic✨ companions, fr fr.

2003-2026, The Open MPI Community

and that's a wrap, my love 🫶 the manual page you just read was SHMEM_LONGLONG_WAIT_UNTIL(3) from Open MPI, dropped on Sep 10, 2026 — go forth and wait for your variables to change, you absolute main character. no notes. periodt. 💖✨🎀

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