.\" $OpenBSD: membar_sync.9,v 1.3 2014/02/14 05:11:55 dlg Exp $
.\"
.\" Copyright (c) 2007, 2008 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 $Mdocdate: February 14 2014 $
.Dt MEMBAR 9
.Os
.Sh NAME
.Nm membar_enter ,
.Nm membar_exit ,
.Nm membar_producer ,
.Nm membar_consumer ,
.Nm membar_sync
.Nd memory access barrier operations
.Sh SYNOPSIS
.In sys/atomic.h
.Ft void
.Fn membar_enter "void"
.Ft void
.Fn membar_exit "void"
.Ft void
.Fn membar_producer "void"
.Ft void
.Fn membar_consumer "void"
.Ft void
.Fn membar_sync "void"
.Sh DESCRIPTION
The membar set of functions provide an interface for issuing memory barrier
access operations with respect to multiple processors in the system.
.Bl -tag -width "mem"
.It Fn membar_enter
Any store preceding
.Fn membar_enter
will reach global visibility before all loads and stores following it.
.Pp
.Fn membar_enter
is typically used in code that implements locking primitives to ensure
that a lock protects its data.
.It Fn membar_exit
All loads and stores preceding
.Fn membar_exit
will reach global visibility before any store that follows it.
.Pp
.Fn membar_exit
is typically used in code that implements locking primitives to ensure
that a lock protects its data.
.It Fn membar_producer
All stores preceding the memory barrier will reach global visibility
before any stores after the memory barrier reach global visibility.
.It Fn membar_consumer
All loads preceding the memory barrier will complete before any loads
after the memory barrier complete.
.It Fn membar_sync
All loads and stores preceding the memory barrier will complete and
reach global visibility before any loads and stores after the memory
barrier complete and reach global visibility.
.El
.Sh CONTEXT
.Fn membar_enter ,
.Fn membar_exit ,
.Fn membar_producer ,
.Fn membar_consumer ,
.Fn membar_sync
can all be called during autoconf, from process context, or from interrupt context.
.Sh HISTORY
The membar functions first appeared in
.Nx 5.0
and
.Ox 5.5 .