<!DOCTYPE html><htmllang="en"><head><metacharset="utf-8"><metaname="viewport"content="width=device-width, initial-scale=1.0"><metaname="generator"content="rustdoc"><metaname="description"content="Acquire a critical section in the current thread."><title>acquire in critical_section - Rust</title><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/SourceSerif4-Bold-a2c9cd1067f8b328.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><linkrel="stylesheet"href="../static.files/normalize-76eba96aa4d2e634.css"><linkrel="stylesheet"href="../static.files/rustdoc-fa3bb1812debf86c.css"><metaname="rustdoc-vars"data-root-path="../"data-static-root-path="../static.files/"data-current-crate="critical_section"data-themes=""data-resource-suffix=""data-rustdoc-version="1.75.0-nightly (2bbb61989 2023-10-04)"data-channel="nightly"data-search-js="search-8be46b629f5f14a8.js"data-settings-js="settings-74424d7eec62a23e.js"><scriptsrc="../static.files/storage-fec3eaa3851e447d.js"></script><scriptdefersrc="sidebar-items.js"></script><scriptdefersrc="../static.files/main-c5bd66d33317d69f.js"></script><noscript><linkrel="stylesheet"href="../static.files/noscript-5d8b3c7633ad77ba.css"></noscript><linkrel="alternate icon"type="image/png"href="../static.files/favicon-16x16-8b506e7a72182f1c.png"><linkrel="alternate icon"type="image/png"href="../static.files/favicon-32x32-422f7d1d52889060.png"><linkrel="icon"type="image/svg+xml"href="../static.files/favicon-2c020d218678b618.svg"></head><bodyclass="rustdoc fn"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><navclass="mobile-topbar"><buttonclass="sidebar-menu-toggle">☰</button><aclass="logo-container"href="../critical_section/index.html"><imgclass="rust-logo"src="../static.files/rust-logo-151179464ae7ed46.svg"alt="logo"></a></nav><navclass="sidebar"><aclass="logo-container"href="../critical_section/index.html"><imgclass="rust-logo"src="../static.files/rust-logo-151179464ae7ed46.svg"alt="logo"></a><divclass="sidebar-elems"><h2><ahref="index.html">In critical_section</a></h2></div></nav><main><divclass="width-limiter"><navclass="sub"><formclass="search-form"><span></span><inputclass="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"><divid="help-button"title="help"tabindex="-1"><ahref="../help.html">?</a></div><divid="settings-menu"tabindex="-1"><ahref="../settings.html"title="settings"><imgwidth="22"height="22"alt="Change settings"src="../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><sectionid="main-content"class="content"><divclass="main-heading"><h1>Function <ahref="index.html">critical_section</a>::<wbr><aclass="fn"href="#">acquire</a><buttonid="copy-path"title="Copy item path to clipboard"><imgsrc="../static.files/clipboard-7571035ce49a181d.svg"width="19"height="18"alt="Copy item path"></button></h1><spanclass="out-of-band"><aclass="src"href="../src/critical_section/lib.rs.html#177-184">source</a> · <buttonid="toggle-all-docs"title="collapse all docs">[<span>−</span>]</button></span></div><preclass="rust item-decl"><code>pub unsafe fn acquire() -><aclass="struct"href="struct.RestoreState.html"title="structcritical_section::
<p>This function is extremely low level. Strongly prefer using <ahref="fn.with.html"title="fn critical_section::with"><code>with</code></a> instead.</p>
<p>Nesting critical sections is allowed. The inner critical sections
are mostly no-ops since they’re already protected by the outer one.</p>
<h2id="safety"><ahref="#safety">Safety</a></h2>
<ul>
<li>Each <code>acquire</code> call must be paired with exactly one <code>release</code> call in the same thread.</li>
<li><code>acquire</code> returns a “restore state” that you must pass to the corresponding <code>release</code> call.</li>
<li><code>acquire</code>/<code>release</code> pairs must be “properly nested”, ie it’s not OK to do <code>a=acquire(); b=acquire(); release(a); release(b);</code>.</li>
<li>It is UB to call <code>release</code> if the critical section is not acquired in the current thread.</li>
<li>It is UB to call <code>release</code> with a “restore state” that does not come from the corresponding <code>acquire</code> call.</li>
<li>It must provide ordering guarantees at least equivalent to a [<code>core::sync::atomic::Ordering::Acquire</code>]
on a memory location shared by all critical sections, on which the <code>release</code> call will do a
