MEMBAR(9)

💅 MEMBAR(9) — the memory barrier glow-up ✨

okay so this is a page from the Kernel Developer's Manual, and it's all about membar_enter, membar_exit, membar_producer, membar_consumer, membar_sync, membar_enter_after_atomic, and membar_exit_before_atomic — aka the memory access barrier operations bestie 🫶

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🌸 SYNOPSIS 🌸

#include <sys/atomic.h>

void
membar_enter(void);

void
membar_exit(void);

void
membar_producer(void);

void
membar_consumer(void);

void
membar_sync(void);

void
membar_enter_after_atomic(void);

void
membar_exit_before_atomic(void);

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🦋 DESCRIPTION 🦋

the membar set of functions is literally the interface for issuing memory barrier access operations with respect to multiple processors in the system. multi-core brainrot, but make it correct 💅

membar_enter()

any store preceding membar_enter() will reach global visibility before all loads and stores following it. the way that ordering just works 😭

membar_enter() is typically used in code that implements locking primitives, to ensure that a lock protects its data. icon behavior, no cap.

membar_exit()

all loads and stores preceding membar_exit() will reach global visibility before any store that follows it. slay.

membar_exit() is typically used in code that implements locking primitives, to ensure that a lock protects its data. same energy, other end of the lock 🎀

membar_producer()

all stores preceding the memory barrier will reach global visibility before any stores after the memory barrier reach global visibility. store-then-store, in order, periodt.

membar_consumer()

all loads preceding the memory barrier will complete before any loads after the memory barrier complete. load-then-load, sequenced, we love to see it ⭐

membar_sync()

all loads and stores preceding the memory barrier will complete and reach global visibility before any loads and stores after the memory barrier complete and reach global visibility. the full order-everything special, main character energy 👑

membar_enter_after_atomic()

an atomic operation preceding membar_enter_after_atomic() will reach global visibility before all loads and stores following it. the atomic operation is used to protect the start of a critical section. iykyk 🔥

membar_exit_before_atomic()

all loads and stores preceding membar_exit_before_atomic() will reach global visibility before the atomic operation that follows it. the atomic operation is used to protect the end of a critical section. matching set fr fr 💖

okay so the atomic operations you're allowed to pair with membar_enter_after_atomic() and membar_exit_before_atomic() are the atomic_add, atomic_sub, atomic_inc, atomic_dec, and atomic_cas set of functions. for other cases, use membar_enter() or membar_exit() — don't be out here freelancing 🙈

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🌈 CONTEXT 🌈

membar_enter(), membar_exit(), membar_producer(), membar_consumer(), membar_sync(), membar_enter_after_atomic(), and membar_exit_before_atomic() can all be called during autoconf, from process context, or from interrupt context. versatile kings, every single one 💜

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🎀 HISTORY 🎀

the membar functions first appeared in NetBSD 5.0 and OpenBSD 5.5. vintage, but make it iconic ✨

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and that's the whole page, bestie — this one's from the Debian crew, dated March 13, 2022, and it's giving "kernel dev textbook but the group chat explained it better." go forth and barrier your memory correctly 🧚💅