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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 `split` fn in crate `rayon`."><meta name="keywords" content="rust, rustlang, rust-lang, split"><title>rayon::iter::split - 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 fn"><!--[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='../../rayon/index.html'><div class='logo-container'><img src='../../rust-logo.png' alt='logo'></div></a><div class="sidebar-elems"><p class='location'><a href='../index.html'>rayon</a>::<wbr><a href='index.html'>iter</a></p><script>window.sidebarCurrent = {name: 'split', ty: 'fn', 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"><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/rayon/iter/splitter.rs.html#106-112' title='goto source code'>[src]</a></span><span class='in-band'>Function <a href='../index.html'>rayon</a>::<wbr><a href='index.html'>iter</a>::<wbr><a class="fn" href=''>split</a></span></h1><pre class='rust fn'>pub fn split<D, S>(data: D, splitter: S) -> <a class="struct" href="../../rayon/iter/struct.Split.html" title="struct rayon::iter::Split">Split</a><D, S> <span class="where fmt-newline">where<br> D: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a>,<br> S: <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/function/trait.Fn.html" title="trait core::ops::function::Fn">Fn</a>(D) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.tuple.html">(</a>D, <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><D><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.tuple.html">)</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a>, </span></pre><div class='docblock'><p>The <code>split</code> function takes arbitrary data and a closure that knows how to
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split it, and turns this into a <code>ParallelIterator</code>.</p>
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<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
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<p>As a simple example, Rayon can recursively split ranges of indices</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">rayon</span>::<span class="ident">iter</span>;
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<span class="kw">use</span> <span class="ident">rayon</span>::<span class="ident">prelude</span>::<span class="kw-2">*</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">ops</span>::<span class="ident">Range</span>;
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<span class="comment">// We define a range of indices as follows</span>
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<span class="kw">type</span> <span class="ident">Range1D</span> <span class="op">=</span> <span class="ident">Range</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>;
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<span class="comment">// Splitting it in two can be done like this</span>
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<span class="kw">fn</span> <span class="ident">split_range1</span>(<span class="ident">r</span>: <span class="ident">Range1D</span>) <span class="op">-</span><span class="op">></span> (<span class="ident">Range1D</span>, <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Range1D</span><span class="op">></span>) {
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<span class="comment">// We are mathematically unable to split the range if there is only</span>
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<span class="comment">// one point inside of it, but we could stop splitting before that.</span>
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<span class="kw">if</span> <span class="ident">r</span>.<span class="ident">end</span> <span class="op">-</span> <span class="ident">r</span>.<span class="ident">start</span> <span class="op"><</span><span class="op">=</span> <span class="number">1</span> { <span class="kw">return</span> (<span class="ident">r</span>, <span class="prelude-val">None</span>); }
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<span class="comment">// Here, our range is considered large enough to be splittable</span>
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<span class="kw">let</span> <span class="ident">midpoint</span> <span class="op">=</span> <span class="ident">r</span>.<span class="ident">start</span> <span class="op">+</span> (<span class="ident">r</span>.<span class="ident">end</span> <span class="op">-</span> <span class="ident">r</span>.<span class="ident">start</span>) <span class="op">/</span> <span class="number">2</span>;
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(<span class="ident">r</span>.<span class="ident">start</span>..<span class="ident">midpoint</span>, <span class="prelude-val">Some</span>(<span class="ident">midpoint</span>..<span class="ident">r</span>.<span class="ident">end</span>))
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}
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<span class="comment">// By using iter::split, Rayon will split the range until it has enough work</span>
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<span class="comment">// to feed the CPU cores, then give us the resulting sub-ranges</span>
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<span class="ident">iter</span>::<span class="ident">split</span>(<span class="number">0</span>..<span class="number">4096</span>, <span class="ident">split_range1</span>).<span class="ident">for_each</span>(<span class="op">|</span><span class="ident">sub_range</span><span class="op">|</span> {
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<span class="comment">// As our initial range had a power-of-two size, the final sub-ranges</span>
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<span class="comment">// should have power-of-two sizes too</span>
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<span class="macro">assert</span><span class="macro">!</span>((<span class="ident">sub_range</span>.<span class="ident">end</span> <span class="op">-</span> <span class="ident">sub_range</span>.<span class="ident">start</span>).<span class="ident">is_power_of_two</span>());
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});</pre></div>
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<p>This recursive splitting can be extended to two or three dimensions,
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to reproduce a classic "block-wise" parallelization scheme of graphics and
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numerical simulations:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="comment">// A two-dimensional range of indices can be built out of two 1D ones</span>
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<span class="kw">struct</span> <span class="ident">Range2D</span> {
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<span class="comment">// Range of horizontal indices</span>
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<span class="kw">pub</span> <span class="ident">rx</span>: <span class="ident">Range1D</span>,
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<span class="comment">// Range of vertical indices</span>
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<span class="kw">pub</span> <span class="ident">ry</span>: <span class="ident">Range1D</span>,
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}
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<span class="comment">// We want to recursively split them by the largest dimension until we have</span>
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<span class="comment">// enough sub-ranges to feed our mighty multi-core CPU. This function</span>
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<span class="comment">// carries out one such split.</span>
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<span class="kw">fn</span> <span class="ident">split_range2</span>(<span class="ident">r2</span>: <span class="ident">Range2D</span>) <span class="op">-</span><span class="op">></span> (<span class="ident">Range2D</span>, <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Range2D</span><span class="op">></span>) {
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<span class="comment">// Decide on which axis (horizontal/vertical) the range should be split</span>
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<span class="kw">let</span> <span class="ident">width</span> <span class="op">=</span> <span class="ident">r2</span>.<span class="ident">rx</span>.<span class="ident">end</span> <span class="op">-</span> <span class="ident">r2</span>.<span class="ident">rx</span>.<span class="ident">start</span>;
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<span class="kw">let</span> <span class="ident">height</span> <span class="op">=</span> <span class="ident">r2</span>.<span class="ident">ry</span>.<span class="ident">end</span> <span class="op">-</span> <span class="ident">r2</span>.<span class="ident">ry</span>.<span class="ident">start</span>;
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<span class="kw">if</span> <span class="ident">width</span> <span class="op">></span><span class="op">=</span> <span class="ident">height</span> {
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<span class="comment">// This is a wide range, split it on the horizontal axis</span>
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<span class="kw">let</span> (<span class="ident">split_rx</span>, <span class="ident">ry</span>) <span class="op">=</span> (<span class="ident">split_range1</span>(<span class="ident">r2</span>.<span class="ident">rx</span>), <span class="ident">r2</span>.<span class="ident">ry</span>);
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<span class="kw">let</span> <span class="ident">out1</span> <span class="op">=</span> <span class="ident">Range2D</span> {
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<span class="ident">rx</span>: <span class="ident">split_rx</span>.<span class="number">0</span>,
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<span class="ident">ry</span>: <span class="ident">ry</span>.<span class="ident">clone</span>(),
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};
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<span class="kw">let</span> <span class="ident">out2</span> <span class="op">=</span> <span class="ident">split_rx</span>.<span class="number">1</span>.<span class="ident">map</span>(<span class="op">|</span><span class="ident">rx</span><span class="op">|</span> <span class="ident">Range2D</span> { <span class="ident">rx</span>, <span class="ident">ry</span> });
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(<span class="ident">out1</span>, <span class="ident">out2</span>)
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} <span class="kw">else</span> {
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<span class="comment">// This is a tall range, split it on the vertical axis</span>
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<span class="kw">let</span> (<span class="ident">rx</span>, <span class="ident">split_ry</span>) <span class="op">=</span> (<span class="ident">r2</span>.<span class="ident">rx</span>, <span class="ident">split_range1</span>(<span class="ident">r2</span>.<span class="ident">ry</span>));
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<span class="kw">let</span> <span class="ident">out1</span> <span class="op">=</span> <span class="ident">Range2D</span> {
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<span class="ident">rx</span>: <span class="ident">rx</span>.<span class="ident">clone</span>(),
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<span class="ident">ry</span>: <span class="ident">split_ry</span>.<span class="number">0</span>,
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};
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<span class="kw">let</span> <span class="ident">out2</span> <span class="op">=</span> <span class="ident">split_ry</span>.<span class="number">1</span>.<span class="ident">map</span>(<span class="op">|</span><span class="ident">ry</span><span class="op">|</span> <span class="ident">Range2D</span> { <span class="ident">rx</span>, <span class="ident">ry</span>, });
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(<span class="ident">out1</span>, <span class="ident">out2</span>)
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}
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}
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<span class="comment">// Again, rayon can handle the recursive splitting for us</span>
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<span class="kw">let</span> <span class="ident">range</span> <span class="op">=</span> <span class="ident">Range2D</span> { <span class="ident">rx</span>: <span class="number">0</span>..<span class="number">800</span>, <span class="ident">ry</span>: <span class="number">0</span>..<span class="number">600</span> };
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<span class="ident">iter</span>::<span class="ident">split</span>(<span class="ident">range</span>, <span class="ident">split_range2</span>).<span class="ident">for_each</span>(<span class="op">|</span><span class="ident">sub_range</span><span class="op">|</span> {
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<span class="comment">// If the sub-ranges were indeed split by the largest dimension, then</span>
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<span class="comment">// if no dimension was twice larger than the other initially, this</span>
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<span class="comment">// property will remain true in the final sub-ranges.</span>
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<span class="kw">let</span> <span class="ident">width</span> <span class="op">=</span> <span class="ident">sub_range</span>.<span class="ident">rx</span>.<span class="ident">end</span> <span class="op">-</span> <span class="ident">sub_range</span>.<span class="ident">rx</span>.<span class="ident">start</span>;
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<span class="kw">let</span> <span class="ident">height</span> <span class="op">=</span> <span class="ident">sub_range</span>.<span class="ident">ry</span>.<span class="ident">end</span> <span class="op">-</span> <span class="ident">sub_range</span>.<span class="ident">ry</span>.<span class="ident">start</span>;
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<span class="macro">assert</span><span class="macro">!</span>((<span class="ident">width</span> <span class="op">/</span> <span class="number">2</span> <span class="op"><</span><span class="op">=</span> <span class="ident">height</span>) <span class="kw-2">&</span><span class="op">&</span> (<span class="ident">height</span> <span class="op">/</span> <span class="number">2</span> <span class="op"><</span><span class="op">=</span> <span class="ident">width</span>));
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});</pre></div>
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