Standard C Library Functions                       membarops(3C)



NAME
     membarops,  membarenter,   membarexit,   membarproducer,
     membarconsumer  -  memory  access  synchronization  barrier
     operations

SYNOPSIS
     #include 

     void membarenter(void);


     void membarexit(void);


     void membarproducer(void);


     void membarconsumer(void);


DESCRIPTION
     The membarenter() 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 visibil-
     ity.


     The membarexit() function is a generic memory barrier  used
     during lock exit. It is placed before the      memory opera-
     tion that releases the lock to guarantee that the lock  pro-
     tects  its data. All loads and stores issued before the bar-
     rier      will be resolved before the subsequent lock update
     reaches visibility.


     The membarenter()  and  membarexit()  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  main-
     tained at a higher level. They are useful in the implementa-
     tion of mutex exclusion locks.


     The  membarproducer()  function  arranges  for  all  stores
     issued  before  this point in the code to reach global visi-
     bility before any stores that follow. This is useful in pro-
     ducer  modules that update a data item, then set a flag that
     it is available. The  memory  barrier  guarantees  that  the
     available flag is not visible earlier than the updated data,
     thereby imposing store ordering.



SunOS 5.11          Last change: 14 Feb 2005                    1






Standard C Library Functions                       membarops(3C)



     The membarconsumer() 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 ord-
     ering.

RETURN VALUES
     No values are returned.

ERORS
     No errors are defined.

ATRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     
           ATRIBUTE TYPE               ATRIBUTE VALUE       
    
     Interface Stability          Stable                      
    
     MT-Level                     MT-Safe                     
    


SEE ALSO
     atomicadd(3C),       atomicand(3C),       atomicbits(3C),
     atomiccas(3C),        atomicdec(3C),       atomicinc(3C),
     atomicops(3C),   atomicor(3C),   atomicswap(3C),   attri-
     butes(5), atomicops(9F)

NOTES
     Atomic instructions (see atomicops(3C)) ensure global visi-
     bility  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  synchroniza-
     tion is required, memory barrier instructions must be used.













SunOS 5.11          Last change: 14 Feb 2005                    2