<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="generator" content="rustdoc">
<meta name="description" content="API documentation for the Rust `fence` fn in crate `std`.">
<meta name="keywords" content="rust, rustlang, rust-lang, fence">
<title>std::sync::atomic::fence - Rust</title>
<link rel="stylesheet" type="text/css" href="../../../normalize.css">
<link rel="stylesheet" type="text/css" href="../../../rustdoc.css">
<link rel="stylesheet" type="text/css" href="../../../main.css">
<link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico">
</head>
<body class="rustdoc fn">
<!--[if lte IE 8]>
<div class="warning">
This old browser is unsupported and will most likely display funky
things.
</div>
<![endif]-->
<nav class="sidebar">
<a href='../../../std/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a>
<p class='location'><a href='../../index.html'>std</a>::<wbr><a href='../index.html'>sync</a>::<wbr><a href='index.html'>atomic</a></p><script>window.sidebarCurrent = {name: 'fence', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script>
</nav>
<nav class="sub">
<form class="search-form js-only">
<div class="search-container">
<input class="search-input" name="search"
autocomplete="off"
placeholder="Click or press ‘S’ to search, ‘?’ for more options…"
type="search">
</div>
</form>
</nav>
<section id='main' class="content">
<h1 class='fqn'><span class='in-band'>Function <a href='../../index.html'>std</a>::<wbr><a href='../index.html'>sync</a>::<wbr><a href='index.html'>atomic</a>::<wbr><a class="fn" href=''>fence</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><span id='render-detail'>
<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
[<span class='inner'>−</span>]
</a>
</span><a class='srclink' href='../../../src/core/sync/atomic.rs.html#1653-1664' title='goto source code'>[src]</a></span></h1>
<pre class='rust fn'>pub fn fence(order: <a class="enum" href="../../../std/sync/atomic/enum.Ordering.html" title="enum std::sync::atomic::Ordering">Ordering</a>)</pre><div class='docblock'><p>An atomic fence.</p>
<p>Depending on the specified order, a fence prevents the compiler and CPU from
reordering certain types of memory operations around it.
That creates synchronizes-with relationships between it and atomic operations
or fences in other threads.</p>
<p>A fence 'A' which has (at least) <a href="enum.Ordering.html#variant.Release"><code>Release</code></a> ordering semantics, synchronizes
with a fence 'B' with (at least) <a href="enum.Ordering.html#variant.Acquire"><code>Acquire</code></a> semantics, if and only if there
exist operations X and Y, both operating on some atomic object 'M' such
that A is sequenced before X, Y is synchronized before B and Y observes
the change to M. This provides a happens-before dependence between A and B.</p>
<pre><code class="language-text"> Thread 1 Thread 2
fence(Release); A --------------
x.store(3, Relaxed); X --------- |
| |
| |
-------------> Y if x.load(Relaxed) == 3 {
|-------> B fence(Acquire);
...
}
</code></pre>
<p>Atomic operations with <a href="enum.Ordering.html#variant.Release"><code>Release</code></a> or <a href="enum.Ordering.html#variant.Acquire"><code>Acquire</code></a> semantics can also synchronize
with a fence.</p>
<p>A fence which has <a href="enum.Ordering.html#variant.SeqCst"><code>SeqCst</code></a> ordering, in addition to having both <a href="enum.Ordering.html#variant.Acquire"><code>Acquire</code></a>
and <a href="enum.Ordering.html#variant.Release"><code>Release</code></a> semantics, participates in the global program order of the
other <a href="enum.Ordering.html#variant.SeqCst"><code>SeqCst</code></a> operations and/or fences.</p>
<p>Accepts <a href="enum.Ordering.html#variant.Acquire"><code>Acquire</code></a>, <a href="enum.Ordering.html#variant.Release"><code>Release</code></a>, <a href="enum.Ordering.html#variant.AcqRel"><code>AcqRel</code></a> and <a href="enum.Ordering.html#variant.SeqCst"><code>SeqCst</code></a> orderings.</p>
<h1 id='panics' class='section-header'><a href='#panics'>Panics</a></h1>
<p>Panics if <code>order</code> is <a href="enum.Ordering.html#variant.Relaxed"><code>Relaxed</code></a>.</p>
<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">atomic</span>::<span class="ident">AtomicBool</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">atomic</span>::<span class="ident">fence</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">atomic</span>::<span class="ident">Ordering</span>;
<span class="comment">// A mutual exclusion primitive based on spinlock.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Mutex</span> {
<span class="ident">flag</span>: <span class="ident">AtomicBool</span>,
}
<span class="kw">impl</span> <span class="ident">Mutex</span> {
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-></span> <span class="ident">Mutex</span> {
<span class="ident">Mutex</span> {
<span class="ident">flag</span>: <span class="ident">AtomicBool</span>::<span class="ident">new</span>(<span class="bool-val">false</span>),
}
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">lock</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">while</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">flag</span>.<span class="ident">compare_and_swap</span>(<span class="bool-val">false</span>, <span class="bool-val">true</span>, <span class="ident">Ordering</span>::<span class="ident">Relaxed</span>) {}
<span class="comment">// This fence syncronizes-with store in `unlock`.</span>
<span class="ident">fence</span>(<span class="ident">Ordering</span>::<span class="ident">Acquire</span>);
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">unlock</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="self">self</span>.<span class="ident">flag</span>.<span class="ident">store</span>(<span class="bool-val">false</span>, <span class="ident">Ordering</span>::<span class="ident">Release</span>);
}
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=fn%20main()%20%7B%0Ause%20std%3A%3Async%3A%3Aatomic%3A%3AAtomicBool%3B%0Ause%20std%3A%3Async%3A%3Aatomic%3A%3Afence%3B%0Ause%20std%3A%3Async%3A%3Aatomic%3A%3AOrdering%3B%0A%0A%2F%2F%20A%20mutual%20exclusion%20primitive%20based%20on%20spinlock.%0Apub%20struct%20Mutex%20%7B%0A%20%20%20%20flag%3A%20AtomicBool%2C%0A%7D%0A%0Aimpl%20Mutex%20%7B%0A%20%20%20%20pub%20fn%20new()%20-%3E%20Mutex%20%7B%0A%20%20%20%20%20%20%20%20Mutex%20%7B%0A%20%20%20%20%20%20%20%20%20%20%20%20flag%3A%20AtomicBool%3A%3Anew(false)%2C%0A%20%20%20%20%20%20%20%20%7D%0A%20%20%20%20%7D%0A%0A%20%20%20%20pub%20fn%20lock(%26self)%20%7B%0A%20%20%20%20%20%20%20%20while%20!self.flag.compare_and_swap(false%2C%20true%2C%20Ordering%3A%3ARelaxed)%20%7B%7D%0A%20%20%20%20%20%20%20%20%2F%2F%20This%20fence%20syncronizes-with%20store%20in%20%60unlock%60.%0A%20%20%20%20%20%20%20%20fence(Ordering%3A%3AAcquire)%3B%0A%20%20%20%20%7D%0A%0A%20%20%20%20pub%20fn%20unlock(%26self)%20%7B%0A%20%20%20%20%20%20%20%20self.flag.store(false%2C%20Ordering%3A%3ARelease)%3B%0A%20%20%20%20%7D%0A%7D%0A%7D">Run</a></pre>
</div></section>
<section id='search' class="content hidden"></section>
<section class="footer"></section>
<aside id="help" class="hidden">
<div>
<h1 class="hidden">Help</h1>
<div class="shortcuts">
<h2>Keyboard Shortcuts</h2>
<dl>
<dt>?</dt>
<dd>Show this help dialog</dd>
<dt>S</dt>
<dd>Focus the search field</dd>
<dt>⇤</dt>
<dd>Move up in search results</dd>
<dt>⇥</dt>
<dd>Move down in search results</dd>
<dt>⏎</dt>
<dd>Go to active search result</dd>
<dt>+</dt>
<dd>Collapse/expand all sections</dd>
</dl>
</div>
<div class="infos">
<h2>Search Tricks</h2>
<p>
Prefix searches with a type followed by a colon (e.g.
<code>fn:</code>) to restrict the search to a given type.
</p>
<p>
Accepted types are: <code>fn</code>, <code>mod</code>,
<code>struct</code>, <code>enum</code>,
<code>trait</code>, <code>type</code>, <code>macro</code>,
and <code>const</code>.
</p>
<p>
Search functions by type signature (e.g.
<code>vec -> usize</code> or <code>* -> vec</code>)
</p>
</div>
</div>
</aside>
<script>
window.rootPath = "../../../";
window.currentCrate = "std";
</script>
<script src="../../../main.js"></script>
<script defer src="../../../search-index.js"></script>
</body>
</html>
distrib
>
Mageia
>
6
>
armv7hl
>
media
>
core-updates
>
by-pkgid
>
564935689ab5527f955e5449ded02799
>
files
>
5082
