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membar_ops(9F) Kernel Functions for Drivers membar_ops(9F)
NAME
membar_ops, membar_enter, membar_exit, membar_producer, membar_consumer
- memory access synchronization barrier operations
SYNOPSIS
#include <sys/atomic.h>
void membar_enter(void);
void membar_exit(void);
void membar_producer(void);
void membar_consumer(void);
DESCRIPTION
The membar_enter() function is a generic memory barrier used during
lock entry. It is placed after the memory operation that acquires the
lock to guarantee that the lock protects its data. No stores from after
the memory barrier will reach visibility and no loads from after the
barrier will be resolved before the lock acquisition reaches global
visibility.
The membar_exit() function is a generic memory barrier used during lock
exit. It is placed before the memory operation that releases the lock
to guarantee that the lock protects its data. All loads and stores
issued before the barrier will be resolved before the subsequent lock
update reaches visibility.
The membar_enter() and membar_exit() functions are used together to
allow regions of code to be in relaxed store order and then ensure that
the load or store order is maintained at a higher level. They are use‐
ful in the implementation of mutex exclusion locks.
The membar_producer() function arranges for all stores issued before
this point in the code to reach global visibility before any stores
that follow. This is useful in producer modules that update a data
item, then set a flag that it is available. The memory barrier guaran‐
tees that the available flag is not visible earlier than the updated
data, thereby imposing store ordering.
The membar_consumer() function arranges for all loads issued before
this point in the code to be completed before any subsequent loads.
This is useful in consumer modules that check if data is available and
read the data. The memory barrier guarantees that the data is not sam‐
pled until after the available flag has been seen, thereby imposing
load ordering.
RETURN VALUES
No values are returned.
ERRORS
No errors are defined.
CONTEXT
These functions can be called from user, interrupt, or kernel context.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Evolving │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSO
atomic_add(9F), atomic_and(9F), atomic_bits(9F), atomic_cas(9F),
atomic_dec(9F), atomic_inc(9F), atomic_ops(9F), atomic_or(9F),
atomic_swap(9F), attributes(5), atomic_ops(3C)
NOTES
Atomic instructions (see atomic_ops(9F)) ensure global visibility of
atomically-modified variables on completion. In a relaxed store order
system, this does not guarantee that the visibility of other variables
will be synchronized with the completion of the atomic instruction. If
such synchronization is required, memory barrier instructions must be
used.
SunOS 5.10 16 Jan 2006 membar_ops(9F)
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