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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="API documentation for the Rust `num_cpus` crate."><meta name="keywords" content="rust, rustlang, rust-lang, num_cpus"><title>num_cpus - 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><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="shortcut icon" href="../favicon.ico"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></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='../num_cpus/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><p class='location'>Crate num_cpus</p><div class="sidebar-elems"><a id='all-types' href='all.html'><p>See all num_cpus's items</p></a><div class="block items"><ul><li><a href="#functions">Functions</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'num_cpus', ty: 'mod', relpath: '../'};</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"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><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='out-of-band'><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/num_cpus/lib.rs.html#1-483' title='goto source code'>[src]</a></span><span class='in-band'>Crate <a class="mod" href=''>num_cpus</a></span></h1><div class='docblock'><p>A crate with utilities to determine the number of CPUs available on the
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current system.</p>
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<p>Sometimes the CPU will exaggerate the number of CPUs it contains, because it can use
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<a href="https://en.wikipedia.org/wiki/Simultaneous_multithreading">processor tricks</a> to deliver increased performance when there are more threads. This
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crate provides methods to get both the logical and physical numbers of cores.</p>
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<p>This information can be used as a guide to how many tasks can be run in parallel.
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There are many properties of the system architecture that will affect parallelism,
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for example memory access speeds (for all the caches and RAM) and the physical
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architecture of the processor, so the number of CPUs should be used as a rough guide
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only.</p>
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<h2 id="examples" class="section-header"><a href="#examples">Examples</a></h2>
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<p>Fetch the number of logical CPUs.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">let</span> <span class="ident">cpus</span> <span class="op">=</span> <span class="ident">num_cpus</span>::<span class="ident">get</span>();</pre></div>
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<p>See <a href="https://docs.rs/rayon/1.*/rayon/struct.ThreadPool.html"><code>rayon::Threadpool</code></a> for an example of where the number of CPUs could be
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used when setting up parallel jobs (Where the threadpool example uses a fixed
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number 8, it could use the number of CPUs).</p>
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</div><h2 id='functions' class='section-header'><a href="#functions">Functions</a></h2>
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<table><tr class='module-item'><td><a class="fn" href="fn.get.html" title='num_cpus::get fn'>get</a></td><td class='docblock-short'><p>Returns the number of available CPUs of the current system.</p>
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</td></tr><tr class='module-item'><td><a class="fn" href="fn.get_physical.html" title='num_cpus::get_physical fn'>get_physical</a></td><td class='docblock-short'><p>Returns the number of physical cores of the current system.</p>
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