1.\" $OpenBSD: membar_sync.9,v 1.3 2014/02/14 05:11:55 dlg Exp $ 2.\" 3.\" Copyright (c) 2007, 2008 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Jason R. Thorpe. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd $Mdocdate: February 14 2014 $ 31.Dt MEMBAR 9 32.Os 33.Sh NAME 34.Nm membar_enter , 35.Nm membar_exit , 36.Nm membar_producer , 37.Nm membar_consumer , 38.Nm membar_sync 39.Nd memory access barrier operations 40.Sh SYNOPSIS 41.In sys/atomic.h 42.Ft void 43.Fn membar_enter "void" 44.Ft void 45.Fn membar_exit "void" 46.Ft void 47.Fn membar_producer "void" 48.Ft void 49.Fn membar_consumer "void" 50.Ft void 51.Fn membar_sync "void" 52.Sh DESCRIPTION 53The membar set of functions provide an interface for issuing memory barrier 54access operations with respect to multiple processors in the system. 55.Bl -tag -width "mem" 56.It Fn membar_enter 57Any store preceding 58.Fn membar_enter 59will reach global visibility before all loads and stores following it. 60.Pp 61.Fn membar_enter 62is typically used in code that implements locking primitives to ensure 63that a lock protects its data. 64.It Fn membar_exit 65All loads and stores preceding 66.Fn membar_exit 67will reach global visibility before any store that follows it. 68.Pp 69.Fn membar_exit 70is typically used in code that implements locking primitives to ensure 71that a lock protects its data. 72.It Fn membar_producer 73All stores preceding the memory barrier will reach global visibility 74before any stores after the memory barrier reach global visibility. 75.It Fn membar_consumer 76All loads preceding the memory barrier will complete before any loads 77after the memory barrier complete. 78.It Fn membar_sync 79All loads and stores preceding the memory barrier will complete and 80reach global visibility before any loads and stores after the memory 81barrier complete and reach global visibility. 82.El 83.Sh CONTEXT 84.Fn membar_enter , 85.Fn membar_exit , 86.Fn membar_producer , 87.Fn membar_consumer , 88.Fn membar_sync 89can all be called during autoconf, from process context, or from interrupt context. 90.Sh HISTORY 91The membar functions first appeared in 92.Nx 5.0 93and 94.Ox 5.5 . 95