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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 `select` macro in crate `crossbeam_channel`."><meta name="keywords" content="rust, rustlang, rust-lang, select"><title>crossbeam_channel::select - 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 macro"><!--[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='../crossbeam_channel/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'>crossbeam_channel</a></p><script>window.sidebarCurrent = {name: 'select', ty: 'macro', 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/crossbeam_channel/select_macro.rs.html#1195-1201' title='goto source code'>[src]</a></span><span class='in-band'>Macro <a href='index.html'>crossbeam_channel</a>::<wbr><a class="macro" href=''>select</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><div class="example-wrap"><pre class="rust macro">
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<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">select</span> {
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($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">tokens</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=</span><span class="op">></span> { ... };
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}</pre></div>
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</div><div class='docblock'><p>Selects from a set of channel operations.</p>
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<p>This macro allows you to define a set of channel operations, wait until any one of them becomes
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ready, and finally execute it. If multiple operations are ready at the same time, a random one
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among them is selected.</p>
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<p>It is also possible to define a <code>default</code> case that gets executed if none of the operations are
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ready, either right away or for a certain duration of time.</p>
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<p>An operation is considered to be ready if it doesn't have to block. Note that it is ready even
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when it will simply return an error because the channel is disconnected.</p>
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<p>The <code>select</code> macro is a convenience wrapper around <a href="struct.Select.html"><code>Select</code></a>. However, it cannot select over a
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dynamically created list of channel operations.</p>
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<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
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<p>Block until a send or a receive operation is selected:</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">std</span>::<span class="ident">thread</span>;
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<span class="kw">use</span> <span class="ident">crossbeam_channel</span>::<span class="ident">unbounded</span>;
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<span class="kw">let</span> (<span class="ident">s1</span>, <span class="ident">r1</span>) <span class="op">=</span> <span class="ident">unbounded</span>();
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<span class="kw">let</span> (<span class="ident">s2</span>, <span class="ident">r2</span>) <span class="op">=</span> <span class="ident">unbounded</span>();
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<span class="ident">s1</span>.<span class="ident">send</span>(<span class="number">10</span>).<span class="ident">unwrap</span>();
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<span class="comment">// Since both operations are initially ready, a random one will be executed.</span>
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<span class="macro">select</span><span class="macro">!</span> {
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<span class="ident">recv</span>(<span class="ident">r1</span>) <span class="op">-</span><span class="op">></span> <span class="ident">msg</span> <span class="op">=</span><span class="op">></span> <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">msg</span>, <span class="prelude-val">Ok</span>(<span class="number">10</span>)),
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<span class="ident">send</span>(<span class="ident">s2</span>, <span class="number">20</span>) <span class="op">-</span><span class="op">></span> <span class="ident">res</span> <span class="op">=</span><span class="op">></span> {
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">res</span>, <span class="prelude-val">Ok</span>(()));
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">r2</span>.<span class="ident">recv</span>(), <span class="prelude-val">Ok</span>(<span class="number">20</span>));
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}
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}</pre></div>
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<p>Select from a set of operations without blocking:</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">std</span>::<span class="ident">thread</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">time</span>::<span class="ident">Duration</span>;
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<span class="kw">use</span> <span class="ident">crossbeam_channel</span>::<span class="ident">unbounded</span>;
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<span class="kw">let</span> (<span class="ident">s1</span>, <span class="ident">r1</span>) <span class="op">=</span> <span class="ident">unbounded</span>();
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<span class="kw">let</span> (<span class="ident">s2</span>, <span class="ident">r2</span>) <span class="op">=</span> <span class="ident">unbounded</span>();
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<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> {
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<span class="ident">thread</span>::<span class="ident">sleep</span>(<span class="ident">Duration</span>::<span class="ident">from_secs</span>(<span class="number">1</span>));
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<span class="ident">s1</span>.<span class="ident">send</span>(<span class="number">10</span>).<span class="ident">unwrap</span>();
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});
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<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> {
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<span class="ident">thread</span>::<span class="ident">sleep</span>(<span class="ident">Duration</span>::<span class="ident">from_millis</span>(<span class="number">500</span>));
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<span class="ident">s2</span>.<span class="ident">send</span>(<span class="number">20</span>).<span class="ident">unwrap</span>();
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});
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<span class="comment">// None of the operations are initially ready.</span>
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<span class="macro">select</span><span class="macro">!</span> {
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<span class="ident">recv</span>(<span class="ident">r1</span>) <span class="op">-</span><span class="op">></span> <span class="ident">msg</span> <span class="op">=</span><span class="op">></span> <span class="macro">panic</span><span class="macro">!</span>(),
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<span class="ident">recv</span>(<span class="ident">r2</span>) <span class="op">-</span><span class="op">></span> <span class="ident">msg</span> <span class="op">=</span><span class="op">></span> <span class="macro">panic</span><span class="macro">!</span>(),
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<span class="ident">default</span> <span class="op">=</span><span class="op">></span> <span class="macro">println</span><span class="macro">!</span>(<span class="string">"not ready"</span>),
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}</pre></div>
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<p>Select over a set of operations with a timeout:</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">std</span>::<span class="ident">thread</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">time</span>::<span class="ident">Duration</span>;
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<span class="kw">use</span> <span class="ident">crossbeam_channel</span>::<span class="ident">unbounded</span>;
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<span class="kw">let</span> (<span class="ident">s1</span>, <span class="ident">r1</span>) <span class="op">=</span> <span class="ident">unbounded</span>();
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<span class="kw">let</span> (<span class="ident">s2</span>, <span class="ident">r2</span>) <span class="op">=</span> <span class="ident">unbounded</span>();
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<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> {
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<span class="ident">thread</span>::<span class="ident">sleep</span>(<span class="ident">Duration</span>::<span class="ident">from_secs</span>(<span class="number">1</span>));
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<span class="ident">s1</span>.<span class="ident">send</span>(<span class="number">10</span>).<span class="ident">unwrap</span>();
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});
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<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> {
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<span class="ident">thread</span>::<span class="ident">sleep</span>(<span class="ident">Duration</span>::<span class="ident">from_millis</span>(<span class="number">500</span>));
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<span class="ident">s2</span>.<span class="ident">send</span>(<span class="number">20</span>).<span class="ident">unwrap</span>();
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});
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<span class="comment">// None of the two operations will become ready within 100 milliseconds.</span>
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<span class="macro">select</span><span class="macro">!</span> {
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<span class="ident">recv</span>(<span class="ident">r1</span>) <span class="op">-</span><span class="op">></span> <span class="ident">msg</span> <span class="op">=</span><span class="op">></span> <span class="macro">panic</span><span class="macro">!</span>(),
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<span class="ident">recv</span>(<span class="ident">r2</span>) <span class="op">-</span><span class="op">></span> <span class="ident">msg</span> <span class="op">=</span><span class="op">></span> <span class="macro">panic</span><span class="macro">!</span>(),
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<span class="ident">default</span>(<span class="ident">Duration</span>::<span class="ident">from_millis</span>(<span class="number">100</span>)) <span class="op">=</span><span class="op">></span> <span class="macro">println</span><span class="macro">!</span>(<span class="string">"timed out"</span>),
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}</pre></div>
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<p>Optionally add a receive operation to <code>select!</code> using <a href="fn.never.html"><code>never</code></a>:</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">std</span>::<span class="ident">thread</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">time</span>::<span class="ident">Duration</span>;
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<span class="kw">use</span> <span class="ident">crossbeam_channel</span>::{<span class="ident">never</span>, <span class="ident">unbounded</span>};
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<span class="kw">let</span> (<span class="ident">s1</span>, <span class="ident">r1</span>) <span class="op">=</span> <span class="ident">unbounded</span>();
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<span class="kw">let</span> (<span class="ident">s2</span>, <span class="ident">r2</span>) <span class="op">=</span> <span class="ident">unbounded</span>();
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<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> {
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<span class="ident">thread</span>::<span class="ident">sleep</span>(<span class="ident">Duration</span>::<span class="ident">from_secs</span>(<span class="number">1</span>));
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<span class="ident">s1</span>.<span class="ident">send</span>(<span class="number">10</span>).<span class="ident">unwrap</span>();
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});
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<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> {
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<span class="ident">thread</span>::<span class="ident">sleep</span>(<span class="ident">Duration</span>::<span class="ident">from_millis</span>(<span class="number">500</span>));
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<span class="ident">s2</span>.<span class="ident">send</span>(<span class="number">20</span>).<span class="ident">unwrap</span>();
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});
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<span class="comment">// This receiver can be a `Some` or a `None`.</span>
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<span class="kw">let</span> <span class="ident">r2</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="ident">r2</span>);
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<span class="comment">// None of the two operations will become ready within 100 milliseconds.</span>
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<span class="macro">select</span><span class="macro">!</span> {
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<span class="ident">recv</span>(<span class="ident">r1</span>) <span class="op">-</span><span class="op">></span> <span class="ident">msg</span> <span class="op">=</span><span class="op">></span> <span class="macro">panic</span><span class="macro">!</span>(),
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<span class="ident">recv</span>(<span class="ident">r2</span>.<span class="ident">unwrap_or</span>(<span class="kw-2">&</span><span class="ident">never</span>())) <span class="op">-</span><span class="op">></span> <span class="ident">msg</span> <span class="op">=</span><span class="op">></span> <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">msg</span>, <span class="prelude-val">Ok</span>(<span class="number">20</span>)),
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}</pre></div>
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<p>To optionally add a timeout to <code>select!</code>, see the <a href="fn.never.html#examples">example</a> for <a href="fn.never.html"><code>never</code></a>.</p>
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</div></section><section id="search" class="content hidden"></section><section class="footer"></section><aside id="help" class="hidden"><div><h1 class="hidden">Help</h1><div class="shortcuts"><h2>Keyboard Shortcuts</h2><dl><dt><kbd>?</kbd></dt><dd>Show this help dialog</dd><dt><kbd>S</kbd></dt><dd>Focus the search field</dd><dt><kbd>↑</kbd></dt><dd>Move up in search results</dd><dt><kbd>↓</kbd></dt><dd>Move down in search results</dd><dt><kbd>↹</kbd></dt><dd>Switch tab</dd><dt><kbd>⏎</kbd></dt><dd>Go to active search result</dd><dt><kbd>+</kbd></dt><dd>Expand all sections</dd><dt><kbd>-</kbd></dt><dd>Collapse all sections</dd></dl></div><div class="infos"><h2>Search Tricks</h2><p>Prefix searches with a type followed by a colon (e.g., <code>fn:</code>) to restrict the search to a given type.</p><p>Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>.</p><p>Search functions by type signature (e.g., <code>vec -> usize</code> or <code>* -> vec</code>)</p><p>Search multiple things at once by splitting your query with comma (e.g., <code>str,u8</code> or <code>String,struct:Vec,test</code>)</p></div></div></aside><script>window.rootPath = "../";window.currentCrate = "crossbeam_channel";</script><script src="../aliases.js"></script><script src="../main.js"></script><script defer src="../search-index.js"></script></body></html> |
