membar_sync(9) – memory access barrier operations

NAME

membar_enter, membar_exit, membar_producer, membar_consumer, membar_sync, membar_enter_after_atomic, membar_exit_before_atomic — memory access barrier operations

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);

DESCRIPTION

The membar set of functions provide an interface for issuing memory barrier access operations with respect to multiple processors in the system.

membar_enter(): Any store preceding membar_enter() will reach global visibility before all loads and stores following it.
membar_enter() is typically used in code that implements locking primitives to ensure that a lock protects its data.
membar_exit(): All loads and stores preceding membar_exit() will reach global visibility before any store that follows it.
membar_exit() is typically used in code that implements locking primitives to ensure that a lock protects its data.
membar_producer(): All stores preceding the memory barrier will reach global visibility before any stores after the memory barrier reach global visibility.
membar_consumer(): All loads preceding the memory barrier will complete before any loads after the memory barrier complete.
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.
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.
membar_exit_before_atomic(): All loads and stores preceding membar_exit_before_atomic() will reach global visibility before atomic operation that follows it. The atomic operation is used to protect the end of a critical section.

The atomic operations that can be used 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().

CONTEXT

membar_enter(), membar_exit(), membar_producer(), membar_consumer(), membar_sync(), membar_enter_after_atomic(), membar_exit_before_atomic() can all be called during autoconf, from process context, or from interrupt context.

HISTORY

The membar functions first appeared in NetBSD 5.0 and OpenBSD 5.5.