ATOMIC_OPS(3C) Standard C Library Functions ATOMIC_OPS(3C)

NAME

atomic_ops - atomic operations

SYNOPSIS

#include <atomic.h>

DESCRIPTION

This collection of functions provides atomic memory operations. There are
8 different classes of atomic operations:

atomic_add(3C)
These functions provide an atomic addition of a signed
value to a variable.


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


atomic_bits(3C)
These functions provide atomic bit setting and
clearing within a variable.


atomic_cas(3C)
These functions provide an atomic comparison 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.


atomic_dec(3C)
These functions provide an atomic decrement on a
variable.


atomic_inc(3C)
These functions provide an atomic increment on a
variable.


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


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

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Stable |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO

atomic_add(3C), atomic_and(3C), atomic_bits(3C), atomic_cas(3C),
atomic_dec(3C), atomic_inc(3C), atomic_or(3C), atomic_swap(3C),
membar_ops(3C), attributes(7)

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 membar_ops(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 atomic_inc(3C) operation on each of them.

August 12, 2004 ATOMIC_OPS(3C)