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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="Selects from a set of channel operations."><title>select in crossbeam_channel - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-Medium-e1aa3f0a.woff2,SourceCodePro-Regular-8badfe75.ttf.woff2,SourceCodePro-Semibold-aa29a496.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../static.files/rustdoc-42caa33d.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="crossbeam_channel" data-themes="" data-resource-suffix="" data-rustdoc-version="1.84.1 (e71f9a9a9 2025-01-27)" data-channel="1.84.1" data-search-js="search-92e6798f.js" data-settings-js="settings-0f613d39.js" ><script src="../static.files/storage-59e33391.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-5f194d8c.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-893ab5e7.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-6580c154.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-044be391.svg"></head><body class="rustdoc macro"><!--[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" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../crossbeam_channel/index.html">crossbeam_<wbr>channel</a><span class="version">0.5.13</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">select</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#examples" title="Examples">Examples</a></li></ul></section><div id="rustdoc-modnav"><h2 class="in-crate"><a href="index.html">In crate crossbeam_<wbr>channel</a></h2></div></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><span class="rustdoc-breadcrumbs"><a href="index.html">crossbeam_channel</a></span><h1>Macro <span class="macro">select</span><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../src/crossbeam_channel/select_macro.rs.html#1111-1121">Source</a> </span></div><pre class="rust item-decl"><code>macro_rules! select {
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($($tokens:tt)*) => { ... };
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}</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><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 (i.e. the unbiased selection). Use <code>select_biased!</code> for the biased
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selection.</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" title="struct crossbeam_channel::Select"><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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<h2 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h2>
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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"><code><span class="kw">use </span>crossbeam_channel::{select, unbounded};
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<span class="kw">let </span>(s1, r1) = unbounded();
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<span class="kw">let </span>(s2, r2) = unbounded();
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s1.send(<span class="number">10</span>).unwrap();
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<span class="comment">// Since both operations are initially ready, a random one will be executed.
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</span><span class="macro">select!</span> {
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recv(r1) -> msg => <span class="macro">assert_eq!</span>(msg, <span class="prelude-val">Ok</span>(<span class="number">10</span>)),
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send(s2, <span class="number">20</span>) -> res => {
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<span class="macro">assert_eq!</span>(res, <span class="prelude-val">Ok</span>(()));
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<span class="macro">assert_eq!</span>(r2.recv(), <span class="prelude-val">Ok</span>(<span class="number">20</span>));
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}
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}</code></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"><code><span class="kw">use </span>std::thread;
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<span class="kw">use </span>std::time::Duration;
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<span class="kw">use </span>crossbeam_channel::{select, unbounded};
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<span class="kw">let </span>(s1, r1) = unbounded();
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<span class="kw">let </span>(s2, r2) = unbounded();
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thread::spawn(<span class="kw">move </span>|| {
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thread::sleep(Duration::from_secs(<span class="number">1</span>));
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s1.send(<span class="number">10</span>).unwrap();
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});
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thread::spawn(<span class="kw">move </span>|| {
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thread::sleep(Duration::from_millis(<span class="number">500</span>));
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s2.send(<span class="number">20</span>).unwrap();
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});
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<span class="comment">// None of the operations are initially ready.
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</span><span class="macro">select!</span> {
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recv(r1) -> msg => <span class="macro">panic!</span>(),
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recv(r2) -> msg => <span class="macro">panic!</span>(),
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default => <span class="macro">println!</span>(<span class="string">"not ready"</span>),
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}</code></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"><code><span class="kw">use </span>std::thread;
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<span class="kw">use </span>std::time::Duration;
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<span class="kw">use </span>crossbeam_channel::{select, unbounded};
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<span class="kw">let </span>(s1, r1) = unbounded();
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<span class="kw">let </span>(s2, r2) = unbounded();
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thread::spawn(<span class="kw">move </span>|| {
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thread::sleep(Duration::from_secs(<span class="number">1</span>));
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s1.send(<span class="number">10</span>).unwrap();
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});
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thread::spawn(<span class="kw">move </span>|| {
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thread::sleep(Duration::from_millis(<span class="number">500</span>));
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s2.send(<span class="number">20</span>).unwrap();
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});
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<span class="comment">// None of the two operations will become ready within 100 milliseconds.
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</span><span class="macro">select!</span> {
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recv(r1) -> msg => <span class="macro">panic!</span>(),
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recv(r2) -> msg => <span class="macro">panic!</span>(),
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default(Duration::from_millis(<span class="number">100</span>)) => <span class="macro">println!</span>(<span class="string">"timed out"</span>),
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}</code></pre></div>
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<p>Optionally add a receive operation to <code>select!</code> using <a href="fn.never.html" title="fn crossbeam_channel::never"><code>never</code></a>:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::thread;
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<span class="kw">use </span>std::time::Duration;
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<span class="kw">use </span>crossbeam_channel::{select, never, unbounded};
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<span class="kw">let </span>(s1, r1) = unbounded();
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<span class="kw">let </span>(s2, r2) = unbounded();
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thread::spawn(<span class="kw">move </span>|| {
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thread::sleep(Duration::from_secs(<span class="number">1</span>));
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s1.send(<span class="number">10</span>).unwrap();
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});
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thread::spawn(<span class="kw">move </span>|| {
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thread::sleep(Duration::from_millis(<span class="number">500</span>));
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s2.send(<span class="number">20</span>).unwrap();
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});
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<span class="comment">// This receiver can be a `Some` or a `None`.
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</span><span class="kw">let </span>r2 = <span class="prelude-val">Some</span>(<span class="kw-2">&</span>r2);
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<span class="comment">// None of the two operations will become ready within 100 milliseconds.
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</span><span class="macro">select!</span> {
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recv(r1) -> msg => <span class="macro">panic!</span>(),
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recv(r2.unwrap_or(<span class="kw-2">&</span>never())) -> msg => <span class="macro">assert_eq!</span>(msg, <span class="prelude-val">Ok</span>(<span class="number">20</span>)),
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}</code></pre></div>
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<p>To optionally add a timeout to <code>select!</code>, see the <a href="fn.never.html#examples" title="fn crossbeam_channel::never">example</a> for <a href="fn.never.html" title="fn crossbeam_channel::never"><code>never</code></a>.</p>
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</div></details></section></div></main></body></html> |