b6cbf7203b
This patch imports the unmodified current version of NetBSD libc. The NetBSD includes are in /nbsd_include, while the libc code itself is split between lib/nbsd_libc and common/lib/libc.
129 lines
4.5 KiB
Groff
129 lines
4.5 KiB
Groff
.\" $NetBSD: atomic_cas.3,v 1.2 2010/02/12 22:23:17 dyoung Exp $
|
|
.\"
|
|
.\" Copyright (c) 2007, 2010 The NetBSD Foundation, Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to The NetBSD Foundation
|
|
.\" by Jason R. Thorpe.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
|
|
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
|
|
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
|
|
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
|
|
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
|
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
|
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
|
|
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
|
|
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
|
|
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
|
|
.\" POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.Dd February 11, 2010
|
|
.Dt ATOMIC_CAS 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm atomic_cas ,
|
|
.Nm atomic_cas_32 ,
|
|
.Nm atomic_cas_uint ,
|
|
.Nm atomic_cas_ulong ,
|
|
.Nm atomic_cas_ptr ,
|
|
.Nm atomic_cas_64 ,
|
|
.Nm atomic_cas_32_ni ,
|
|
.Nm atomic_cas_uint_ni ,
|
|
.Nm atomic_cas_ulong_ni ,
|
|
.Nm atomic_cas_ptr_ni ,
|
|
.Nm atomic_cas_64_ni
|
|
.Nd atomic compare-and-swap operations
|
|
.\" .Sh LIBRARY
|
|
.\" .Lb libc
|
|
.Sh SYNOPSIS
|
|
.In sys/atomic.h
|
|
.Ft uint32_t
|
|
.Fn atomic_cas_32 "volatile uint32_t *ptr" "uint32_t old" "uint32_t new"
|
|
.Ft unsigned int
|
|
.Fn atomic_cas_uint "volatile unsigned int *ptr" "unsigned int old" \
|
|
"unsigned int new"
|
|
.Ft unsigned long
|
|
.Fn atomic_cas_ulong "volatile unsigned long *ptr" "unsigned long old" \
|
|
"unsigned long new"
|
|
.Ft void *
|
|
.Fn atomic_cas_ptr "volatile void *ptr" "void *old" "void *new"
|
|
.Ft uint64_t
|
|
.Fn atomic_cas_64 "volatile uint64_t *ptr" "uint64_t old" "uint64_t new"
|
|
.Ft uint32_t
|
|
.Fn atomic_cas_32_ni "volatile uint32_t *ptr" "uint32_t old" "uint32_t new"
|
|
.Ft unsigned int
|
|
.Fn atomic_cas_uint_ni "volatile unsigned int *ptr" "unsigned int old" \
|
|
"unsigned int new"
|
|
.Ft unsigned long
|
|
.Fn atomic_cas_ulong_ni "volatile unsigned long *ptr" "unsigned long old" \
|
|
"unsigned long new"
|
|
.Ft void *
|
|
.Fn atomic_cas_ptr_ni "volatile void *ptr" "void *old" "void *new"
|
|
.Ft uint64_t
|
|
.Fn atomic_cas_64_ni "volatile uint64_t *ptr" "uint64_t old" "uint64_t new"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm atomic_cas
|
|
family of functions perform a compare-and-swap operation in an atomic fashion.
|
|
The value of the variable referenced by
|
|
.Fa ptr
|
|
is compared against
|
|
.Fa old .
|
|
If the values are equal,
|
|
.Fa new
|
|
is stored in the variable referenced by
|
|
.Fa ptr .
|
|
.Pp
|
|
The old value of the variable referenced by
|
|
.Fa ptr
|
|
is always returned regardless of whether or not the new value was stored.
|
|
Applications can test for success of the operation by comparing the
|
|
return value to the value passed as
|
|
.Fa old ;
|
|
if they are equal then the new value was stored.
|
|
.Pp
|
|
The non-interlocked variants,
|
|
.Fn *_ni ,
|
|
guarantee atomicity within the same CPU with respect to
|
|
interrupts and preemption.
|
|
For example, they are suitable for synchronizing compare-and-swap
|
|
operations on a variable shared by a thread and an interrupt
|
|
that are bound to the same CPU.
|
|
The
|
|
.Fn *_ni
|
|
variants are not atomic with respect to different CPUs.
|
|
.Fn *_ni
|
|
variants should avoid the interprocessor synchronization overhead
|
|
of the standard compare-and-swap operations.
|
|
.Pp
|
|
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
|
|
.Dv __HAVE_ATOMIC64_OPS
|
|
is defined.
|
|
.Sh SEE ALSO
|
|
.Xr atomic_ops 3
|
|
.Sh HISTORY
|
|
The
|
|
.Nm atomic_cas
|
|
functions first appeared in
|
|
.Nx 5.0 .
|
|
.Sh NOTES
|
|
On some architectures, a
|
|
.Fn *_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.
|