| ATOMIC_CAS(3) | Library Functions Manual | ATOMIC_CAS(3) | 
atomic_cas, atomic_cas_32,
  atomic_cas_uint,
  atomic_cas_ulong,
  atomic_cas_ptr, atomic_cas_64,
  atomic_cas_32_ni,
  atomic_cas_uint_ni,
  atomic_cas_ulong_ni,
  atomic_cas_ptr_ni,
  atomic_cas_64_ni —
#include <sys/atomic.h>
uint32_t
  
  atomic_cas_32(volatile
    uint32_t *ptr, uint32_t
    expected, uint32_t
    new);
unsigned int
  
  atomic_cas_uint(volatile
    unsigned int *ptr,
    unsigned int expected,
    unsigned int new);
unsigned long
  
  atomic_cas_ulong(volatile
    unsigned long *ptr,
    unsigned long expected,
    unsigned long new);
void *
  
  atomic_cas_ptr(volatile
    void *ptr, void
    *expected, void
    *new);
uint64_t
  
  atomic_cas_64(volatile
    uint64_t *ptr, uint64_t
    expected, uint64_t
    new);
uint32_t
  
  atomic_cas_32_ni(volatile
    uint32_t *ptr, uint32_t
    expected, uint32_t
    new);
unsigned int
  
  atomic_cas_uint_ni(volatile
    unsigned int *ptr,
    unsigned int expected,
    unsigned int new);
unsigned long
  
  atomic_cas_ulong_ni(volatile
    unsigned long *ptr,
    unsigned long expected,
    unsigned long new);
void *
  
  atomic_cas_ptr_ni(volatile
    void *ptr, void
    *expected, void
    *new);
uint64_t
  
  atomic_cas_64_ni(volatile
    uint64_t *ptr, uint64_t
    expected, uint64_t
    new);
atomic_cas family of functions perform an atomic
  conditional assignment. The value new is assigned to the
  variable referenced by ptr. The assignment succeeds if
  and only if its current value matches the value
  expected. If the value is different, the assignment
  fails and no change is made. This operation is sometimes known as
  “compare-and-swap”. These functions always return the value
  found via ptr. Callers test for success by comparing the
  return value to the value passed as expected; if they
  are equal then the new value was stored; if they are not, the value was not
  changed.
The non-interlocked variants, *_ni(),
    guarantee atomicity within the same CPU with respect to interrupts and
    preemption. They are not atomic with respect to different CPUs. These can be
    used to avoid interprocessor synchronization overhead in some cases; for
    example, they are suitable for synchronized operations on a variable shared
    by a thread and an interrupt that are bound to the same CPU.
The 64-bit variants of these functions are available only on
    platforms that can support atomic 64-bit memory access. Applications can
    check for the availability of 64-bit atomic memory operations by testing if
    the pre-processor macro __HAVE_ATOMIC64_OPS is
    defined.
atomic_cas functions first appeared in
  NetBSD 5.0.
*_ni() variant is merely an
  alias for the corresponding standard compare-and-swap operation. While the
  non-interlocked variant behaves correctly on those architectures, it does not
  avoid the interprocessor synchronization overhead.
| February 2, 2014 | NetBSD 9.4 |