<!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" id="mainThemeStyle"> <link rel="stylesheet" type="text/css" href="../../../dark.css"> <link rel="stylesheet" type="text/css" href="../../../main.css" id="themeStyle"> <script src="../../../storage.js"></script> <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"> <div class="sidebar-menu">☰</div> <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> <div class="theme-picker"> <button id="theme-picker" aria-label="Pick another theme!"> <img src="../../../brush.svg" width="18" alt="Pick another theme!"> </button> <div id="theme-choices"></div> </div> <script src="../../../theme.js"></script> <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#1760-1771' 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 synchronizes-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=%23!%5Ballow(unused)%5D%0Afn%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%20synchronizes-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><kbd>?</kbd></dt> <dd>Show this help dialog</dd> <dt><kbd>S</kbd></dt> <dd>Focus the search field</dd> <dt><kbd>↑</kbd></dt> <dd>Move up in search results</dd> <dt><kbd>↓</kbd></dt> <dd>Move down in search results</dd> <dt><kbd>↹</kbd></dt> <dd>Switch tab</dd> <dt><kbd>⏎</kbd></dt> <dd>Go to active search result</dd> <dt><kbd>+</kbd></dt> <dd>Expand all sections</dd> <dt><kbd>-</kbd></dt> <dd>Collapse 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 = "../../../"; 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