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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="Thread-safe, non-blocking, “first one wins” flavor of `OnceCell`."><title>once_cell::race - 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/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-5bc39a1768837dd0.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="once_cell" data-themes="" data-resource-suffix="" data-rustdoc-version="1.77.0 (aedd173a2 2024-03-17)" data-channel="1.77.0" data-search-js="search-dd67cee4cfa65049.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../static.files/storage-4c98445ec4002617.js"></script><script defer src="../sidebar-items.js"></script><script defer src="../../static.files/main-48f368f3872407c8.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-04d5337699b92874.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 mod"><!--[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" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../once_cell/index.html">once_cell</a><span class="version">1.19.0</span></h2></div><h2 class="location"><a href="#">Module race</a></h2><div class="sidebar-elems"><section><ul class="block"><li><a href="#structs">Structs</a></li></ul></section><h2><a href="../index.html">In crate once_cell</a></h2></div></nav><div class="sidebar-resizer"></div>
<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../../once_cell/all.html" title="show sidebar"></a></div><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" tabindex="-1"><a href="../../help.html" title="help">?</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>Module <a href="../index.html">once_cell</a>::<wbr><a class="mod" href="#">race</a><button id="copy-path" title="Copy item path to clipboard"><img src="../../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../../src/once_cell/race.rs.html#1-419">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>&#x2212;</span>]</button></span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Thread-safe, non-blocking, “first one wins” flavor of <code>OnceCell</code>.</p>
<p>If two threads race to initialize a type from the <code>race</code> module, they
dont block, execute initialization function together, but only one of
them stores the result.</p>
<p>This module does not require <code>std</code> feature.</p>
<h2 id="atomic-orderings"><a class="doc-anchor" href="#atomic-orderings">§</a>Atomic orderings</h2>
<p>All types in this module use <code>Acquire</code> and <code>Release</code>
<a href="https://doc.rust-lang.org/1.77.0/core/sync/atomic/enum.Ordering.html" title="enum core::sync::atomic::Ordering">atomic orderings</a> for all their operations. While this is not
strictly necessary for types other than <code>OnceBox</code>, it is useful for users as
it allows them to be certain that after <code>get</code> or <code>get_or_init</code> returns on
one thread, any side-effects caused by the setter thread prior to them
calling <code>set</code> or <code>get_or_init</code> will be made visible to that thread; without
it, its possible for it to appear as if they havent happened yet from the
getter threads perspective. This is an acceptable tradeoff to make since
<code>Acquire</code> and <code>Release</code> have very little performance overhead on most
architectures versus <code>Relaxed</code>.</p>
</div></details><h2 id="structs" class="section-header">Structs<a href="#structs" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="struct" href="struct.OnceBool.html" title="struct once_cell::race::OnceBool">OnceBool</a></div><div class="desc docblock-short">A thread-safe cell which can be written to only once.</div></li><li><div class="item-name"><a class="struct" href="struct.OnceBox.html" title="struct once_cell::race::OnceBox">OnceBox</a></div><div class="desc docblock-short">A thread-safe cell which can be written to only once.</div></li><li><div class="item-name"><a class="struct" href="struct.OnceNonZeroUsize.html" title="struct once_cell::race::OnceNonZeroUsize">OnceNonZeroUsize</a></div><div class="desc docblock-short">A thread-safe cell which can be written to only once.</div></li><li><div class="item-name"><a class="struct" href="struct.OnceRef.html" title="struct once_cell::race::OnceRef">OnceRef</a></div><div class="desc docblock-short">A thread-safe cell which can be written to only once.</div></li></ul></section></div></main></body></html>