SHMEM_INT_WAIT_UNTIL(3)

💖 SHMEM_INT_WAIT_UNTIL(3) 💖 (the Open MPI girlies know)

okay bestie, so this is one of the Open MPI manpages, and it's literally about waiting for a variable on your local processing element (PE) to change. That's the whole vibe. 🦋

Here's the whole squad of functions this page covers:

• shmem_int_wait
• shmem_int_wait_until
• shmem_int4_wait
• shmem_int4_wait_until
• shmem_int8_wait
• shmem_int8_wait_until
• shmem_long_wait
• shmem_long_wait_until
• shmem_longlong_wait
• shmem_longlong_wait_until
• shmem_short_wait
• shmem_short_wait_until
• shmem_wait
• shmem_wait_until

and they all wait for a variable on the local processing element (PE) to change. periodt. ✨

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✨ 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)

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🌸 DESCRIPTION 🌸

so shmem_wait and shmem_wait_until are out here waiting for ivar to get changed by a remote write or an atomic swap issued by a different processor. it's giving point-to-point directed synchronization, and honestly? iconic. 💅

here's the tea:

• 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. communication, but make it ✨synchronized✨.

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.
• ivar — A remotely accessible integer variable that is being updated by another PE. If you are using C/C++, the type of ivar should match that implied in the SYNOPSIS section. If you are 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 are using Fortran, it must be of default kind. If you are 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 — cmp_value must be of type integer. If you are using C/C++, the type of cmp_value should match that implied in the SYNOPSIS section. If you are 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.

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🎀 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

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🫶 SEE ALSO 🫶

• intro_shmem(3)
• shmem_put(3)

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👑 COPYRIGHT 👑

2003-2026, The Open MPI Community

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💀 ngl, the target/value/pe args lowkey wandered in from a different function's page, but they're part of this manpage so we're keeping them, bestie. no edits, no cap. 😭

okay that's the whole thing fr fr — this was the Open MPI SHMEM_INT_WAIT_UNTIL(3) page, dated Sep 10, 2026, brought to you by the Open MPI girlies. go let your variables change. 💖🌸✨