Standard C Library Functions                       atomicops(3C)



NAME
     atomicops - atomic operations

SYNOPSIS
     #include 


DESCRIPTION
     This collection of functions provides atomic  memory  opera-
     tions. There are 8 different classes of atomic operations:

     atomicadd(3C)     These functions provide an  atomic  addi-
                        tion of a signed value to a variable.


     atomicand(3C)     These functions provide an atomic logical
                        'and' of a value to a variable.


     atomicbits(3C)    These functions provide atomic  bit  set-
                        ting and clearing within a variable.


     atomiccas(3C)     These functions provide  an  atomic  com-
                        parison  of  a  value with a variable. If
                        the comparison is equal, then swap  in  a
                        new value for the variable, returning the
                        old value of the variable in either case.


     atomicdec(3C)     These functions provide an atomic  decre-
                        ment on a variable.


     atomicinc(3C)     These functions provide an atomic  incre-
                        ment on a variable.


     atomicor(3C)      These functions provide an atomic logical
                        'or' of a value to a variable.


     atomicswap(3C)    These functions provide an atomic swap of
                        a  value  with  a variable, returning the
                        old value of the variable.


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





SunOS 5.11          Last change: 12 Aug 2004                    1






Standard C Library Functions                       atomicops(3C)



     
           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),
     atomicor(3C),   atomicswap(3C),   membarops(3C),   attri-
     butes(5)

NOTES
     Atomic instructions 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.   See
     membarops(3C).


     Atomic instructions can be  expensive.  since  they  require
     synchronization  to  occur  at  a hardware level. This means
     they should  be  used  with  care  to  ensure  that  forcing
     hardware  level  synchronization  occurs a minimum number of
     times. For example, if you have several variables that  need
     to  be  incremented  as  a  group, and each needs to be done
     atomically, then do so with a mutex lock protecting  all  of
     them  being incremented rather than using the atomicinc(3C)
     operation on each of them.





















SunOS 5.11          Last change: 12 Aug 2004                    2