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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="A one-shot channel is used for sending a single message between asynchronous tasks. The `channel` function is used to create a `Sender` and `Receiver` handle pair that form the channel."><title>tokio::sync::oneshot - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Italic-81dc35de.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-MediumItalic-ccf7e434.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"href="../../../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../../../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../../../static.files/rustdoc-ca0dd0c4.css"><meta name="rustdoc-vars" data-root-path="../../../" data-static-root-path="../../../static.files/" data-current-crate="tokio" data-themes="" data-resource-suffix="" data-rustdoc-version="1.93.1 (01f6ddf75 2026-02-11) (Arch Linux rust 1:1.93.1-1)" data-channel="1.93.1" data-search-js="search-9e2438ea.js" data-stringdex-js="stringdex-a3946164.js" data-settings-js="settings-c38705f0.js" ><script src="../../../static.files/storage-e2aeef58.js"></script><script defer src="../sidebar-items.js"></script><script defer src="../../../static.files/main-a410ff4d.js"></script><noscript><link rel="stylesheet" href="../../../static.files/noscript-263c88ec.css"></noscript><link rel="alternate icon" type="image/png" href="../../../static.files/favicon-32x32-eab170b8.png"><link rel="icon" type="image/svg+xml" href="../../../static.files/favicon-044be391.svg"></head><body class="rustdoc mod"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><rustdoc-topbar><h2><a href="#">Module oneshot</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../../tokio/index.html">tokio</a><span class="version">1.49.0</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">Module oneshot</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#examples" title="Examples">Examples</a></li></ul><h3><a href="#modules">Module Items</a></h3><ul class="block"><li><a href="#modules" title="Modules">Modules</a></li><li><a href="#structs" title="Structs">Structs</a></li><li><a href="#functions" title="Functions">Functions</a></li></ul></section><div id="rustdoc-modnav"><h2><a href="../index.html">In tokio::<wbr>sync</a></h2></div></div></nav><div class="sidebar-resizer" title="Drag to resize sidebar"></div><main><div class="width-limiter"><section id="main-content" class="content"><div class="main-heading"><div class="rustdoc-breadcrumbs"><a href="../../index.html">tokio</a>::<wbr><a href="../index.html">sync</a></div><h1>Module <span>oneshot</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/tokio/sync/oneshot.rs.html#1-1594">Source</a> </span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A one-shot channel is used for sending a single message between
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asynchronous tasks. The <a href="fn.channel.html" title="fn tokio::sync::oneshot::channel"><code>channel</code></a> function is used to create a
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<a href="struct.Sender.html" title="struct tokio::sync::oneshot::Sender"><code>Sender</code></a> and <a href="struct.Receiver.html" title="struct tokio::sync::oneshot::Receiver"><code>Receiver</code></a> handle pair that form the channel.</p>
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<p>The <code>Sender</code> handle is used by the producer to send the value.
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The <code>Receiver</code> handle is used by the consumer to receive the value.</p>
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<p>Each handle can be used on separate tasks.</p>
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<p>Since the <code>send</code> method is not async, it can be used anywhere. This includes
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sending between two runtimes, and using it from non-async code.</p>
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<p>If the <a href="struct.Receiver.html" title="struct tokio::sync::oneshot::Receiver"><code>Receiver</code></a> is closed before receiving a message which has already
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been sent, the message will remain in the channel until the receiver is
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dropped, at which point the message will be dropped immediately.</p>
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<h2 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::sync::oneshot;
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<span class="kw">let </span>(tx, rx) = oneshot::channel();
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tokio::spawn(<span class="kw">async move </span>{
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<span class="kw">if let </span><span class="prelude-val">Err</span>(<span class="kw">_</span>) = tx.send(<span class="number">3</span>) {
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<span class="macro">println!</span>(<span class="string">"the receiver dropped"</span>);
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}
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});
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<span class="kw">match </span>rx.<span class="kw">await </span>{
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<span class="prelude-val">Ok</span>(v) => <span class="macro">println!</span>(<span class="string">"got = {:?}"</span>, v),
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<span class="prelude-val">Err</span>(<span class="kw">_</span>) => <span class="macro">println!</span>(<span class="string">"the sender dropped"</span>),
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}</code></pre></div>
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<p>If the sender is dropped without sending, the receiver will fail with
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<a href="error/struct.RecvError.html" title="struct tokio::sync::oneshot::error::RecvError"><code>error::RecvError</code></a>:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::sync::oneshot;
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<span class="kw">let </span>(tx, rx) = oneshot::channel::<u32>();
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tokio::spawn(<span class="kw">async move </span>{
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drop(tx);
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});
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<span class="kw">match </span>rx.<span class="kw">await </span>{
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<span class="prelude-val">Ok</span>(<span class="kw">_</span>) => <span class="macro">panic!</span>(<span class="string">"This doesn't happen"</span>),
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<span class="prelude-val">Err</span>(<span class="kw">_</span>) => <span class="macro">println!</span>(<span class="string">"the sender dropped"</span>),
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}</code></pre></div>
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<p>To use a <code>oneshot</code> channel in a <code>tokio::select!</code> loop, add <code>&mut</code> in front of
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the channel.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::sync::oneshot;
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<span class="kw">use </span>tokio::time::{interval, sleep, Duration};
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<span class="kw">let </span>(send, <span class="kw-2">mut </span>recv) = oneshot::channel();
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<span class="kw">let </span><span class="kw-2">mut </span>interval = interval(Duration::from_millis(<span class="number">100</span>));
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tokio::spawn(<span class="kw">async move </span>{
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sleep(Duration::from_secs(<span class="number">1</span>)).<span class="kw">await</span>;
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send.send(<span class="string">"shut down"</span>).unwrap();
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});
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<span class="kw">loop </span>{
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<span class="macro">tokio::select!</span> {
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<span class="kw">_ </span>= interval.tick() => <span class="macro">println!</span>(<span class="string">"Another 100ms"</span>),
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msg = <span class="kw-2">&mut </span>recv => {
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<span class="macro">println!</span>(<span class="string">"Got message: {}"</span>, msg.unwrap());
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<span class="kw">break</span>;
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}
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}
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}</code></pre></div>
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<p>To use a <code>Sender</code> from a destructor, put it in an <a href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html" title="enum core::option::Option"><code>Option</code></a> and call
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<a href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html#method.take" title="method core::option::Option::take"><code>Option::take</code></a>.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::sync::oneshot;
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<span class="kw">struct </span>SendOnDrop {
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sender: <span class="prelude-ty">Option</span><oneshot::Sender<<span class="kw-2">&</span><span class="lifetime">'static </span>str>>,
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}
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<span class="kw">impl </span>Drop <span class="kw">for </span>SendOnDrop {
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<span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) {
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<span class="kw">if let </span><span class="prelude-val">Some</span>(sender) = <span class="self">self</span>.sender.take() {
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<span class="comment">// Using `let _ =` to ignore send errors.
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</span><span class="kw">let _ </span>= sender.send(<span class="string">"I got dropped!"</span>);
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}
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}
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}
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<span class="kw">let </span>(send, recv) = oneshot::channel();
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<span class="kw">let </span>send_on_drop = SendOnDrop { sender: <span class="prelude-val">Some</span>(send) };
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drop(send_on_drop);
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<span class="macro">assert_eq!</span>(recv.<span class="kw">await</span>, <span class="prelude-val">Ok</span>(<span class="string">"I got dropped!"</span>));</code></pre></div></div></details><h2 id="modules" class="section-header">Modules<a href="#modules" class="anchor">§</a></h2><dl class="item-table"><dt><a class="mod" href="error/index.html" title="mod tokio::sync::oneshot::error">error</a></dt><dd><code>Oneshot</code> error types.</dd></dl><h2 id="structs" class="section-header">Structs<a href="#structs" class="anchor">§</a></h2><dl class="item-table"><dt><a class="struct" href="struct.Receiver.html" title="struct tokio::sync::oneshot::Receiver">Receiver</a></dt><dd>Receives a value from the associated <a href="struct.Sender.html" title="struct tokio::sync::oneshot::Sender"><code>Sender</code></a>.</dd><dt><a class="struct" href="struct.Sender.html" title="struct tokio::sync::oneshot::Sender">Sender</a></dt><dd>Sends a value to the associated <a href="struct.Receiver.html" title="struct tokio::sync::oneshot::Receiver"><code>Receiver</code></a>.</dd></dl><h2 id="functions" class="section-header">Functions<a href="#functions" class="anchor">§</a></h2><dl class="item-table"><dt><a class="fn" href="fn.channel.html" title="fn tokio::sync::oneshot::channel">channel</a></dt><dd>Creates a new one-shot channel for sending single values across asynchronous
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tasks.</dd></dl></section></div></main></body></html> |