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<!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="An atomic fence."><title>fence in atomic_polyfill - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceSerif4-Bold-a2c9cd1067f8b328.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-cb6f1f67f1bcd037.css" id="mainThemeStyle"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="atomic_polyfill" data-themes="" data-resource-suffix="" data-rustdoc-version="1.73.0-nightly (8131b9774 2023-08-02)" data-channel="nightly" data-search-js="search-6dfdfced5eff6596.js" data-settings-js="settings-de11bff964e9d4e5.js" data-settings-css="settings-8c76f75bfb6bd192.css" data-theme-light-css="light-6d2c9675f3d09c26.css" data-theme-dark-css="dark-45ceb8f2e522f4d1.css" data-theme-ayu-css="ayu-fd19013d6ce078bf.css" ><script src="../static.files/storage-db41da1a38ea3cb8.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-0795b7d26be81095.js"></script><noscript><link rel="stylesheet" media="(prefers-color-scheme:light)" href="../static.files/light-6d2c9675f3d09c26.css"><link rel="stylesheet" media="(prefers-color-scheme:dark)" href="../static.files/dark-45ceb8f2e522f4d1.css"><link rel="stylesheet" href="../static.files/noscript-cffde32267a19fd6.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-16x16-8b506e7a72182f1c.png"><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc fn"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="logo-container" href="../atomic_polyfill/index.html"><img class="rust-logo" src="../static.files/rust-logo-151179464ae7ed46.svg" alt="logo"></a><h2></h2></nav><nav class="sidebar"><a class="logo-container" href="../atomic_polyfill/index.html"><img class="rust-logo" src="../static.files/rust-logo-151179464ae7ed46.svg" alt="logo"></a><div class="sidebar-elems"><h2><a href="index.html">In atomic_polyfill</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Function <a href="index.html">atomic_polyfill</a>::<wbr><a class="fn" href="#">fence</a><button id="copy-path" title="Copy item path to clipboard"><img src="../static.files/clipboard-7571035ce49a181d.svg" width="19" h
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<p>Depending on the specified order, a fence prevents the compiler and CPU from
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reordering certain types of memory operations around it.
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That creates synchronizes-with relationships between it and atomic operations
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or fences in other threads.</p>
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<p>A fence ‘A’ which has (at least) <a href="enum.Ordering.html#variant.Release" title="variant atomic_polyfill::Ordering::Release"><code>Release</code></a> ordering semantics, synchronizes
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with a fence ‘B’ with (at least) <a href="enum.Ordering.html#variant.Acquire" title="variant atomic_polyfill::Ordering::Acquire"><code>Acquire</code></a> semantics, if and only if there
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exist operations X and Y, both operating on some atomic object ‘M’ such
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that A is sequenced before X, Y is sequenced before B and Y observes
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the change to M. This provides a happens-before dependence between A and B.</p>
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<div class="example-wrap"><pre class="language-text"><code> Thread 1 Thread 2
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fence(Release); A --------------
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x.store(3, Relaxed); X --------- |
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-------------> Y if x.load(Relaxed) == 3 {
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|-------> B fence(Acquire);
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...
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}
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</code></pre></div>
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<p>Atomic operations with <a href="enum.Ordering.html#variant.Release" title="variant atomic_polyfill::Ordering::Release"><code>Release</code></a> or <a href="enum.Ordering.html#variant.Acquire" title="variant atomic_polyfill::Ordering::Acquire"><code>Acquire</code></a> semantics can also synchronize
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with a fence.</p>
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<p>A fence which has <a href="enum.Ordering.html#variant.SeqCst" title="variant atomic_polyfill::Ordering::SeqCst"><code>SeqCst</code></a> ordering, in addition to having both <a href="enum.Ordering.html#variant.Acquire" title="variant atomic_polyfill::Ordering::Acquire"><code>Acquire</code></a>
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and <a href="enum.Ordering.html#variant.Release" title="variant atomic_polyfill::Ordering::Release"><code>Release</code></a> semantics, participates in the global program order of the
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other <a href="enum.Ordering.html#variant.SeqCst" title="variant atomic_polyfill::Ordering::SeqCst"><code>SeqCst</code></a> operations and/or fences.</p>
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<p>Accepts <a href="enum.Ordering.html#variant.Acquire" title="variant atomic_polyfill::Ordering::Acquire"><code>Acquire</code></a>, <a href="enum.Ordering.html#variant.Release" title="variant atomic_polyfill::Ordering::Release"><code>Release</code></a>, <a href="enum.Ordering.html#variant.AcqRel" title="variant atomic_polyfill::Ordering::AcqRel"><code>AcqRel</code></a> and <a href="enum.Ordering.html#variant.SeqCst" title="variant atomic_polyfill::Ordering::SeqCst"><code>SeqCst</code></a> orderings.</p>
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<h2 id="panics"><a href="#panics">Panics</a></h2>
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<p>Panics if <code>order</code> is <a href="enum.Ordering.html#variant.Relaxed" title="variant atomic_polyfill::Ordering::Relaxed"><code>Relaxed</code></a>.</p>
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<h2 id="examples"><a href="#examples">Examples</a></h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::sync::atomic::AtomicBool;
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<span class="kw">use </span>std::sync::atomic::fence;
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<span class="kw">use </span>std::sync::atomic::Ordering;
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<span class="comment">// A mutual exclusion primitive based on spinlock.
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</span><span class="kw">pub struct </span>Mutex {
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flag: AtomicBool,
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}
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<span class="kw">impl </span>Mutex {
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<span class="kw">pub fn </span>new() -> Mutex {
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Mutex {
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flag: AtomicBool::new(<span class="bool-val">false</span>),
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}
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}
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<span class="kw">pub fn </span>lock(<span class="kw-2">&</span><span class="self">self</span>) {
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<span class="comment">// Wait until the old value is `false`.
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</span><span class="kw">while </span><span class="self">self
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</span>.flag
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.compare_exchange_weak(<span class="bool-val">false</span>, <span class="bool-val">true</span>, Ordering::Relaxed, Ordering::Relaxed)
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.is_err()
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{}
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<span class="comment">// This fence synchronizes-with store in `unlock`.
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</span>fence(Ordering::Acquire);
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}
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<span class="kw">pub fn </span>unlock(<span class="kw-2">&</span><span class="self">self</span>) {
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<span class="self">self</span>.flag.store(<span class="bool-val">false</span>, Ordering::Release);
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}
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}</code></pre></div>
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</div></details></section></div></main></body></html>
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