SHMEM_LONG_WAIT(3)

💅 SHMEM_LONG_WAIT(3) 💅

okay bestie, welcome to the Open MPI manual page for SHMEM_LONG_WAIT(3) — yes, the title is SHMEM_LONG_WAIT(3) and the manual name is Open MPI, and we're folding both in right here at the top so you have the whole vibe. This page is all about waiting for a variable on the local processing element (PE) to change. Slay. ✨

✨ NAME ✨

shmem_int_wait(3), shmem_int_wait(3)_until, shmem_int4_wait(3), shmem_int4_wait(3)_until, shmem_int8_wait(3), shmem_int8_wait(3)_until, shmem_long_wait(3), shmem_long_wait(3)_until, shmem_longlong_wait(3), shmem_longlong_wait(3)_until, shmem_short_wait(3), shmem_short_wait(3)_until, shmem_wait(3), shmem_wait(3)_until — Waits for a variable on the local processing element (PE) to change

🛠️ 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 💖

okay so shmem_wait and shmem_wait_until wait for ivar to be changed by a remote write or atomic swap issued by a different processor. These routines can be used for point-to-point directed synchronization — think “hey bestie, I'm done, notice me” energy. 💅

A call to shmem_wait does not return until some other processor writes a value, not equal to cmp_value, into ivar on the waiting processor. A call to shmem_wait_until does not return until some other processor changes ivar to satisfy the condition implied by cmp and cmp_value. This mechanism is useful when a processor needs to tell another processor that it has completed some action. No cap. ✨

The arguments are as follows:

• target — the remotely accessible integer data object to be updated on the remote PE. If you're using C/C++, the type of target should match that 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 using C/C++, the type of value should match that implied in the SYNOPSIS section. If you're 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're using Fortran, it must be a default integer value.
• ivar — a remotely accessible integer variable that is being updated by another PE. If you're using C/C++, the type of ivar should match that implied in the SYNOPSIS section. If you're using Fortran, ivar must be a specific sized integer type according to the function being called, as follows:
  • 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 using Fortran, it must be of default kind. If you're using C/C++, the type of cmp should match that implied in the SYNOPSIS section. The following cmp values are supported:
  • 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 — must be of type integer. If you're using C/C++, the type of cmp_value should match that implied in the SYNOPSIS section. If you're using 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. The compare condition is defined by the ivar argument compared with the cmp_value using the comparison operator, cmp.

🌸 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)

👑 COPYRIGHT 👑

2003-2026, The Open MPI Community

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xoxo, your Open MPI bestie 💖 — May 14, 2026 — SHMEM_LONG_WAIT(3) 💅✨