| <!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="Returns a reference to a dummy guard that allows unprotected access to `Atomic`s."><meta name="keywords" content="rust, rustlang, rust-lang, unprotected"><title>unprotected in crossbeam_epoch - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../normalize.css"><link rel="stylesheet" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../ayu.css" disabled><link rel="stylesheet" href="../dark.css" disabled><link rel="stylesheet" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script defer src="sidebar-items.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../favicon.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="sidebar-logo" href="../crossbeam_epoch/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../crossbeam_epoch/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><div class="sidebar-elems"><h2><a href="index.html">In crossbeam_epoch</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" 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="../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Function <a href="index.html">crossbeam_epoch</a>::<wbr><a class="fn" href="#">unprotected</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../src/crossbeam_epoch/guard.rs.html#510-520">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust fn"><code>pub unsafe fn unprotected() -> &'static <a class="struct" href="struct.Guard.html" title="struct crossbeam_epoch::Guard">Guard</a></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Returns a reference to a dummy guard that allows unprotected access to <a href="struct.Atomic.html"><code>Atomic</code></a>s.</p> |
| <p>This guard should be used in special occasions only. Note that it doesn’t actually keep any |
| thread pinned - it’s just a fake guard that allows loading from <a href="struct.Atomic.html"><code>Atomic</code></a>s unsafely.</p> |
| <p>Note that calling <a href="struct.Guard.html#method.defer"><code>defer</code></a> with a dummy guard will not defer the function - it will just |
| execute the function immediately.</p> |
| <p>If necessary, it’s possible to create more dummy guards by cloning: <code>unprotected().clone()</code>.</p> |
| <h2 id="safety"><a href="#safety">Safety</a></h2> |
| <p>Loading and dereferencing data from an <a href="struct.Atomic.html"><code>Atomic</code></a> using this guard is safe only if the |
| <a href="struct.Atomic.html"><code>Atomic</code></a> is not being concurrently modified by other threads.</p> |
| <h2 id="examples"><a href="#examples">Examples</a></h2> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>crossbeam_epoch::{<span class="self">self </span><span class="kw">as </span>epoch, Atomic}; |
| <span class="kw">use </span>std::sync::atomic::Ordering::Relaxed; |
| |
| <span class="kw">let </span>a = Atomic::new(<span class="number">7</span>); |
| |
| <span class="kw">unsafe </span>{ |
| <span class="comment">// Load `a` without pinning the current thread. |
| </span>a.load(Relaxed, epoch::unprotected()); |
| |
| <span class="comment">// It's possible to create more dummy guards by calling `clone()`. |
| </span><span class="kw">let </span>dummy = <span class="kw-2">&</span>epoch::unprotected().clone(); |
| |
| dummy.defer(<span class="kw">move </span>|| { |
| <span class="macro">println!</span>(<span class="string">"This gets executed immediately."</span>); |
| }); |
| |
| <span class="comment">// Dropping `dummy` doesn't affect the current thread - it's just a noop. |
| </span>}</code></pre></div> |
| <p>The most common use of this function is when constructing or destructing a data structure.</p> |
| <p>For example, we can use a dummy guard in the destructor of a Treiber stack because at that |
| point no other thread could concurrently modify the <a href="struct.Atomic.html"><code>Atomic</code></a>s we are accessing.</p> |
| <p>If we were to actually pin the current thread during destruction, that would just unnecessarily |
| delay garbage collection and incur some performance cost, so in cases like these <code>unprotected</code> |
| is very helpful.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>crossbeam_epoch::{<span class="self">self </span><span class="kw">as </span>epoch, Atomic}; |
| <span class="kw">use </span>std::mem::ManuallyDrop; |
| <span class="kw">use </span>std::sync::atomic::Ordering::Relaxed; |
| |
| <span class="kw">struct </span>Stack<T> { |
| head: Atomic<Node<T>>, |
| } |
| |
| <span class="kw">struct </span>Node<T> { |
| data: ManuallyDrop<T>, |
| next: Atomic<Node<T>>, |
| } |
| |
| <span class="kw">impl</span><T> Drop <span class="kw">for </span>Stack<T> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="kw">unsafe </span>{ |
| <span class="comment">// Unprotected load. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>node = <span class="self">self</span>.head.load(Relaxed, epoch::unprotected()); |
| |
| <span class="kw">while let </span><span class="prelude-val">Some</span>(n) = node.as_ref() { |
| <span class="comment">// Unprotected load. |
| </span><span class="kw">let </span>next = n.next.load(Relaxed, epoch::unprotected()); |
| |
| <span class="comment">// Take ownership of the node, then drop its data and deallocate it. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>o = node.into_owned(); |
| ManuallyDrop::drop(<span class="kw-2">&mut </span>o.data); |
| drop(o); |
| |
| node = next; |
| } |
| } |
| } |
| }</code></pre></div> |
| </div></details></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="crossbeam_epoch" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
