membar_ops(3) - NetBSD Manual Pages

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MEMBAR_OPS(3)           NetBSD Library Functions Manual          MEMBAR_OPS(3)


NAME
membar_ops, membar_enter, membar_exit, membar_producer, membar_consumer, membar_datadep_consumer, membar_sync -- 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_datadep_consumer(void); void membar_sync(void);
DESCRIPTION
The membar_ops family of functions provide memory access barrier opera- tions necessary for synchronization in multiprocessor execution environ- ments that have relaxed load and store order. 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 visi- bility 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_datadep_consumer() Same as membar_consumer(), but limited to loads of addresses depen- dent on prior loads, or `data-dependent' loads: int **pp, *p, v; p = *pp; membar_datadep_consumer(); v = *p; consume(v); Does not guarantee ordering of loads in branches, or `control-dependent' loads -- you must use membar_consumer() instead: int *ok, *p, v; if (*ok) { membar_consumer(); v = *p; consume(v); } Most CPUs do not reorder data-dependent loads (i.e., most CPUs guar- antee that cached values are not stale in that case), so membar_datadep_consumer() is a no-op on those CPUs. 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.
SEE ALSO
atomic_ops(3)
HISTORY
The membar_ops functions first appeared in NetBSD 5.0. The data-depen- dent load barrier, membar_datadep_consumer(), first appeared in NetBSD 7.0. NetBSD 9.0 November 20, 2014 NetBSD 9.0
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