0a6a1f1d05
This brings our tree to NetBSD 7.0, as found on -current on the 10-10-2015. This updates: - LLVM to 3.6.1 - GCC to GCC 5.1 - Replace minix/commands/zdump with usr.bin/zdump - external/bsd/libelf has moved to /external/bsd/elftoolchain/ - Import ctwm - Drop sprintf from libminc Change-Id: I149836ac18e9326be9353958bab9b266efb056f0
138 lines
4.1 KiB
Groff
138 lines
4.1 KiB
Groff
.\" $NetBSD: membar_ops.3,v 1.4 2015/01/08 22:27:17 riastradh Exp $
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.\"
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.\" Copyright (c) 2007, 2008 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Jason R. Thorpe.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd November 20, 2014
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.Dt MEMBAR_OPS 3
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.Os
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.Sh NAME
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.Nm membar_ops ,
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.Nm membar_enter ,
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.Nm membar_exit ,
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.Nm membar_producer ,
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.Nm membar_consumer ,
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.Nm membar_sync
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.Nd memory access barrier operations
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.\" .Sh LIBRARY
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.\" .Lb libc
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.Sh SYNOPSIS
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.In sys/atomic.h
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.\"
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.Ft void
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.Fn membar_enter "void"
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.Ft void
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.Fn membar_exit "void"
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.Ft void
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.Fn membar_producer "void"
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.Ft void
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.Fn membar_consumer "void"
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.Ft void
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.Fn membar_datadep_consumer "void"
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.Ft void
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.Fn membar_sync "void"
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.Sh DESCRIPTION
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The
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.Nm membar_ops
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family of functions provide memory access barrier operations necessary
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for synchronization in multiprocessor execution environments that have
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relaxed load and store order.
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.Pp
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.Bl -tag -width "mem"
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.It Fn membar_enter
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Any store preceding
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.Fn membar_enter
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will reach global visibility before all loads and stores following it.
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.Pp
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.Fn membar_enter
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is typically used in code that implements locking primitives to ensure
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that a lock protects its data.
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.It Fn membar_exit
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All loads and stores preceding
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.Fn membar_exit
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will reach global visibility before any store that follows it.
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.Pp
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.Fn membar_exit
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is typically used in code that implements locking primitives to ensure
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that a lock protects its data.
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.It Fn membar_producer
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All stores preceding the memory barrier will reach global visibility
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before any stores after the memory barrier reach global visibility.
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.It Fn membar_consumer
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All loads preceding the memory barrier will complete before any loads
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after the memory barrier complete.
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.It Fn membar_datadep_consumer
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Same as
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.Fn membar_consumer ,
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but limited to loads of addresses dependent on prior loads, or
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.Sq data-dependent
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loads:
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.Bd -literal -offset indent
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int **pp, *p, v;
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p = *pp;
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membar_datadep_consumer();
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v = *p;
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consume(v);
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.Ed
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.Pp
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Does not guarantee ordering of loads in branches, or
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.Sq control-dependent
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loads -- you must use
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.Fn membar_consumer
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instead:
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.Bd -literal -offset indent
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int *ok, *p, v;
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if (*ok) {
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membar_consumer();
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v = *p;
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consume(v);
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}
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.Ed
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.Pp
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Most CPUs do not reorder data-dependent loads (i.e., most CPUs
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guarantee that cached values are not stale in that case), so
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.Fn membar_datadep_consumer
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is a no-op on those CPUs.
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.It Fn membar_sync
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All loads and stores preceding the memory barrier will complete and
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reach global visibility before any loads and stores after the memory
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barrier complete and reach global visibility.
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.El
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.Sh SEE ALSO
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.Xr atomic_ops 3
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.Sh HISTORY
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The
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.Nm membar_ops
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functions first appeared in
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.Nx 5.0 .
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The data-dependent load barrier,
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.Fn membar_datadep_consumer ,
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first appeared in
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.Nx 7.0 .
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