ATOMIC_CAS_UINT(9) | Kernel Developer's Manual | ATOMIC_CAS_UINT(9)

# NAME

`atomic_cas_uint`, `atomic_cas_ulong`, `atomic_cas_ptr` — atomic compare-and-swap operations

# SYNOPSIS

`#include <sys/atomic.h>`

unsigned int
`atomic_cas_uint`(volatile unsigned int *p, unsigned int expected, unsigned int new);

unsigned long
`atomic_cas_ulong`(volatile unsigned long *p, unsigned long expected, unsigned long new);

void *
`atomic_cas_ptr`(volatile void *p, void *expected, void *new);

# DESCRIPTION

The atomic_cas set of functions provide an interface for atomically performing compare-and-swap operations with respect to interrupts and multiple processors in the system.

The value referenced by the pointer p is compared against expected. If these values are equal then new replaces the value stored at p.

# CONTEXT

`atomic_cas_uint`(), `atomic_cas_ulong`(), and `atomic_cas_ptr`() can all be called during autoconf, from process context, or from interrupt context.

# RETURN VALUES

These functions return the value at p as it was before the attempt to swap it.

# SEE ALSO

atomic_swap_uint(9)

# HISTORY

The atomic_cas functions first appeared in NetBSD 5.0 and OpenBSD 5.5.

February 6, 2019 | Debian