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.