SHMEM_SET_LOCK(3)

💖 NAME — shmem_set_lock(3), shmem_clear_lock(3), shmem_test_lock(3) (Open MPI)

okay bestie, gather round: shmem_set_lock(3), shmem_clear_lock(3), and shmem_test_lock(3) are the trio that releases, locks, and tests a mutual exclusion memory lock. periodt. 💅

---

✨ SYNOPSIS ✨

C or C++:

#include <mpp/shmem.h>

void shmem_clear_lock(volatile long *lock)

void shmem_set_lock(volatile long *lock)

int shmem_test_lock(volatile long *lock)

Fortran:

INCLUDE "mpp/shmem.fh"

INTEGER lock, SHMEM_TEST_LOCK

CALL SHMEM_CLEAR_LOCK(lock)

CALL SHMEM_SET_LOCK(lock)

I = SHMEM_TEST_LOCK(lock)

---

🦋 DESCRIPTION 🦋

So the shmem_set_lock routine sets a mutual exclusion lock after waiting for the lock to be freed by any other PE currently holding it. Waiting PEs are assured of getting the lock in a first-come, first-served manner. no cap. 💅

The shmem_clear_lock routine releases a lock previously set by shmem_set_lock after ensuring that all local and remote stores initiated in the critical region are complete. iconic behavior honestly. ✨

The shmem_test_lock function sets a mutual exclusion lock only if it is currently cleared. By using this function, a PE can avoid blocking on a set lock. If the lock is currently set, the function returns without waiting. These routines are appropriate for protecting a critical region from simultaneous update by multiple PEs. They accept the following arguments:

• lock — a symmetric data object that is a scalar variable or an array of length 1. This data object must be set to 0 on all processing elements (PEs) prior to the first use. lock must be of type integer. If you are using Fortran, it must be of default kind. 🫶

---

🌈 NOTES 🌈

The term symmetric data object is defined on intro_shmem(3). iykyk. 🧚

---

👑 RETURN VALUES 👑

The shmem_test_lock function returns 0 if the lock was originally cleared and this call was able to set the lock. A value of 1 is returned if the lock had been set and the call returned without waiting to set the lock. fr fr. 💯

👀 SEE ALSO:

• intro_shmem(3)

---

🎀 COPYRIGHT 🎀

2003-2026, The Open MPI Community

💌 cute little sign-off: this page is from Open MPI, dated May 14, 2026. mwah 💋