membar_ops(9F)															    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);

       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 sub-
       sequent 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 useful 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
       sampled until after the available flag has been seen, thereby imposing load ordering.

       No values are returned.

       No errors are defined.

       These functions can be called from user or interrupt context.

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Evolving			   |
       +-----------------------------+-----------------------------+

       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)

       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.

								    28 Mar 2005 						    membar_ops(9F)