<!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 `atomic` mod in crate `std`."><meta name="keywords" content="rust, rustlang, rust-lang, atomic"><title>std::sync::atomic - 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="../../../light.css" id="themeStyle"><script src="../../../storage.js"></script><link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"></head><body class="rustdoc mod"><!--[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'>Module atomic</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li><li><a href="#constants">Constants</a></li><li><a href="#functions">Functions</a></li></ul></div><p class='location'><a href='../../index.html'>std</a>::<wbr><a href='../index.html'>sync</a></p><script>window.sidebarCurrent = {name: 'atomic', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script></div></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"><a id="settings-menu" href="../../../settings.html"><img src="../../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='in-band'>Module <a href='../../index.html'>std</a>::<wbr><a href='../index.html'>sync</a>::<wbr><a class="mod" href=''>atomic</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/mod.rs.html#15' title='goto source code'>[src]</a></span></h1><div class='docblock'><p>Atomic types</p>
<p>Atomic types provide primitive shared-memory communication between
threads, and are the building blocks of other concurrent
types.</p>
<p>This module defines atomic versions of a select number of primitive
types, including <a href="struct.AtomicBool.html"><code>AtomicBool</code></a>, <a href="struct.AtomicIsize.html"><code>AtomicIsize</code></a>, and <a href="struct.AtomicUsize.html"><code>AtomicUsize</code></a>.
Atomic types present operations that, when used correctly, synchronize
updates between threads.</p>
<p>Each method takes an <a href="enum.Ordering.html"><code>Ordering</code></a> which represents the strength of
the memory barrier for that operation. These orderings are the
same as <a href="http://llvm.org/docs/LangRef.html#memory-model-for-concurrent-operations">LLVM atomic orderings</a>. For more information see the <a href="../../../nomicon/atomics.html">nomicon</a>.</p>
<p>Atomic variables are safe to share between threads (they implement <a href="../../marker/trait.Sync.html"><code>Sync</code></a>)
but they do not themselves provide the mechanism for sharing and follow the
<a href="../../../std/thread/index.html#the-threading-model">threading model</a> of rust.
The most common way to share an atomic variable is to put it into an <a href="../../../std/sync/struct.Arc.html"><code>Arc</code></a> (an
atomically-reference-counted shared pointer).</p>
<p>Most atomic types may be stored in static variables, initialized using
the provided static initializers like <a href="constant.ATOMIC_BOOL_INIT.html"><code>ATOMIC_BOOL_INIT</code></a>. Atomic statics
are often used for lazy global initialization.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>A simple spinlock:</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">Arc</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">atomic</span>::{<span class="ident">AtomicUsize</span>, <span class="ident">Ordering</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">thread</span>;
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">spinlock</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="number">1</span>));
<span class="kw">let</span> <span class="ident">spinlock_clone</span> <span class="op">=</span> <span class="ident">spinlock</span>.<span class="ident">clone</span>();
<span class="kw">let</span> <span class="ident">thread</span> <span class="op">=</span> <span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span><span class="op">||</span> {
<span class="ident">spinlock_clone</span>.<span class="ident">store</span>(<span class="number">0</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
});
<span class="comment">// Wait for the other thread to release the lock</span>
<span class="kw">while</span> <span class="ident">spinlock</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op">!=</span> <span class="number">0</span> {}
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Err</span>(<span class="ident">panic</span>) <span class="op">=</span> <span class="ident">thread</span>.<span class="ident">join</span>() {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"Thread had an error: {:?}"</span>, <span class="ident">panic</span>);
}
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Ause%20std%3A%3Async%3A%3AArc%3B%0Ause%20std%3A%3Async%3A%3Aatomic%3A%3A%7BAtomicUsize%2C%20Ordering%7D%3B%0Ause%20std%3A%3Athread%3B%0A%0Afn%20main()%20%7B%0A%20%20%20%20let%20spinlock%20%3D%20Arc%3A%3Anew(AtomicUsize%3A%3Anew(1))%3B%0A%0A%20%20%20%20let%20spinlock_clone%20%3D%20spinlock.clone()%3B%0A%20%20%20%20let%20thread%20%3D%20thread%3A%3Aspawn(move%7C%7C%20%7B%0A%20%20%20%20%20%20%20%20spinlock_clone.store(0%2C%20Ordering%3A%3ASeqCst)%3B%0A%20%20%20%20%7D)%3B%0A%0A%20%20%20%20%2F%2F%20Wait%20for%20the%20other%20thread%20to%20release%20the%20lock%0A%20%20%20%20while%20spinlock.load(Ordering%3A%3ASeqCst)%20!%3D%200%20%7B%7D%0A%0A%20%20%20%20if%20let%20Err(panic)%20%3D%20thread.join()%20%7B%0A%20%20%20%20%20%20%20%20println!(%22Thread%20had%20an%20error%3A%20%7B%3A%3F%7D%22%2C%20panic)%3B%0A%20%20%20%20%7D%0A%7D">Run</a></pre>
<p>Keep a global count of live threads:</p>
<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">AtomicUsize</span>, <span class="ident">Ordering</span>, <span class="ident">ATOMIC_USIZE_INIT</span>};
<span class="kw">static</span> <span class="ident">GLOBAL_THREAD_COUNT</span>: <span class="ident">AtomicUsize</span> <span class="op">=</span> <span class="ident">ATOMIC_USIZE_INIT</span>;
<span class="kw">let</span> <span class="ident">old_thread_count</span> <span class="op">=</span> <span class="ident">GLOBAL_THREAD_COUNT</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"live threads: {}"</span>, <span class="ident">old_thread_count</span> <span class="op">+</span> <span class="number">1</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%3A%7BAtomicUsize%2C%20Ordering%2C%20ATOMIC_USIZE_INIT%7D%3B%0A%0Astatic%20GLOBAL_THREAD_COUNT%3A%20AtomicUsize%20%3D%20ATOMIC_USIZE_INIT%3B%0A%0Alet%20old_thread_count%20%3D%20GLOBAL_THREAD_COUNT.fetch_add(1%2C%20Ordering%3A%3ASeqCst)%3B%0Aprintln!(%22live%20threads%3A%20%7B%7D%22%2C%20old_thread_count%20%2B%201)%3B%0A%7D">Run</a></pre>
</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
<table>
<tr class=' module-item'>
<td><a class="struct" href="struct.AtomicBool.html"
title='struct std::sync::atomic::AtomicBool'>AtomicBool</a></td>
<td class='docblock-short'>
<p>A boolean type which can be safely shared between threads.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class="struct" href="struct.AtomicIsize.html"
title='struct std::sync::atomic::AtomicIsize'>AtomicIsize</a></td>
<td class='docblock-short'>
<p>An integer type which can be safely shared between threads.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class="struct" href="struct.AtomicPtr.html"
title='struct std::sync::atomic::AtomicPtr'>AtomicPtr</a></td>
<td class='docblock-short'>
<p>A raw pointer type which can be safely shared between threads.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class="struct" href="struct.AtomicUsize.html"
title='struct std::sync::atomic::AtomicUsize'>AtomicUsize</a></td>
<td class='docblock-short'>
<p>An integer type which can be safely shared between threads.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="struct" href="struct.AtomicI8.html"
title='struct std::sync::atomic::AtomicI8'>AtomicI8</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An integer type which can be safely shared between threads.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="struct" href="struct.AtomicI16.html"
title='struct std::sync::atomic::AtomicI16'>AtomicI16</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An integer type which can be safely shared between threads.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="struct" href="struct.AtomicI32.html"
title='struct std::sync::atomic::AtomicI32'>AtomicI32</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An integer type which can be safely shared between threads.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="struct" href="struct.AtomicI64.html"
title='struct std::sync::atomic::AtomicI64'>AtomicI64</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An integer type which can be safely shared between threads.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="struct" href="struct.AtomicU8.html"
title='struct std::sync::atomic::AtomicU8'>AtomicU8</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An integer type which can be safely shared between threads.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="struct" href="struct.AtomicU16.html"
title='struct std::sync::atomic::AtomicU16'>AtomicU16</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An integer type which can be safely shared between threads.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="struct" href="struct.AtomicU32.html"
title='struct std::sync::atomic::AtomicU32'>AtomicU32</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An integer type which can be safely shared between threads.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="struct" href="struct.AtomicU64.html"
title='struct std::sync::atomic::AtomicU64'>AtomicU64</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An integer type which can be safely shared between threads.</p>
</td>
</tr></table><h2 id='enums' class='section-header'><a href="#enums">Enums</a></h2>
<table>
<tr class=' module-item'>
<td><a class="enum" href="enum.Ordering.html"
title='enum std::sync::atomic::Ordering'>Ordering</a></td>
<td class='docblock-short'>
<p>Atomic memory orderings</p>
</td>
</tr></table><h2 id='constants' class='section-header'><a href="#constants">Constants</a></h2>
<table>
<tr class=' module-item'>
<td><a class="constant" href="constant.ATOMIC_BOOL_INIT.html"
title='constant std::sync::atomic::ATOMIC_BOOL_INIT'>ATOMIC_BOOL_INIT</a></td>
<td class='docblock-short'>
<p>An <a href="struct.AtomicBool.html"><code>AtomicBool</code></a> initialized to <code>false</code>.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class="constant" href="constant.ATOMIC_ISIZE_INIT.html"
title='constant std::sync::atomic::ATOMIC_ISIZE_INIT'>ATOMIC_ISIZE_INIT</a></td>
<td class='docblock-short'>
<p>An atomic integer initialized to <code>0</code>.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class="constant" href="constant.ATOMIC_USIZE_INIT.html"
title='constant std::sync::atomic::ATOMIC_USIZE_INIT'>ATOMIC_USIZE_INIT</a></td>
<td class='docblock-short'>
<p>An atomic integer initialized to <code>0</code>.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="constant" href="constant.ATOMIC_I16_INIT.html"
title='constant std::sync::atomic::ATOMIC_I16_INIT'>ATOMIC_I16_INIT</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An atomic integer initialized to <code>0</code>.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="constant" href="constant.ATOMIC_I32_INIT.html"
title='constant std::sync::atomic::ATOMIC_I32_INIT'>ATOMIC_I32_INIT</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An atomic integer initialized to <code>0</code>.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="constant" href="constant.ATOMIC_I64_INIT.html"
title='constant std::sync::atomic::ATOMIC_I64_INIT'>ATOMIC_I64_INIT</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An atomic integer initialized to <code>0</code>.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="constant" href="constant.ATOMIC_I8_INIT.html"
title='constant std::sync::atomic::ATOMIC_I8_INIT'>ATOMIC_I8_INIT</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An atomic integer initialized to <code>0</code>.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="constant" href="constant.ATOMIC_U16_INIT.html"
title='constant std::sync::atomic::ATOMIC_U16_INIT'>ATOMIC_U16_INIT</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An atomic integer initialized to <code>0</code>.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="constant" href="constant.ATOMIC_U32_INIT.html"
title='constant std::sync::atomic::ATOMIC_U32_INIT'>ATOMIC_U32_INIT</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An atomic integer initialized to <code>0</code>.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="constant" href="constant.ATOMIC_U64_INIT.html"
title='constant std::sync::atomic::ATOMIC_U64_INIT'>ATOMIC_U64_INIT</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An atomic integer initialized to <code>0</code>.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="constant" href="constant.ATOMIC_U8_INIT.html"
title='constant std::sync::atomic::ATOMIC_U8_INIT'>ATOMIC_U8_INIT</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>An atomic integer initialized to <code>0</code>.</p>
</td>
</tr></table><h2 id='functions' class='section-header'><a href="#functions">Functions</a></h2>
<table>
<tr class=' module-item'>
<td><a class="fn" href="fn.compiler_fence.html"
title='fn std::sync::atomic::compiler_fence'>compiler_fence</a></td>
<td class='docblock-short'>
<p>A compiler memory fence.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class="fn" href="fn.fence.html"
title='fn std::sync::atomic::fence'>fence</a></td>
<td class='docblock-short'>
<p>An atomic fence.</p>
</td>
</tr>
<tr class=' module-item'>
<td><a class="fn" href="fn.spin_loop_hint.html"
title='fn std::sync::atomic::spin_loop_hint'>spin_loop_hint</a></td>
<td class='docblock-short'>
<p>Save power or switch hyperthreads in a busy-wait spin-loop.</p>
</td>
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