opensolaris man page for membar_producer

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 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.

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	     |Committed 		   |
       +-----------------------------+-----------------------------+

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 5.11							    16 Jan 2006 						    membar_ops(9F)