| <!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 multi-producer, multi-consumer broadcast queue. Each sent value is seen by all consumers."><meta name="keywords" content="rust, rustlang, rust-lang, broadcast"><title>tokio::sync::broadcast - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../normalize.css"><link rel="stylesheet" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../ayu.css" disabled><link rel="stylesheet" href="../../../dark.css" disabled><link rel="stylesheet" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script defer src="../../../main.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../favicon.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]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../../../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Module broadcast</a></h2><div class="sidebar-elems"><section><ul class="block"><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li><li><a href="#functions">Functions</a></li></ul></section></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Module <a href="../../index.html">tokio</a>::<wbr><a href="../index.html">sync</a>::<wbr><a class="mod" href="#">broadcast</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../../../src/tokio/sync/broadcast.rs.html#1-1163">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A multi-producer, multi-consumer broadcast queue. Each sent value is seen by |
| all consumers.</p> |
| <p>A <a href="struct.Sender.html"><code>Sender</code></a> is used to broadcast values to <strong>all</strong> connected <a href="struct.Receiver.html"><code>Receiver</code></a> |
| values. <a href="struct.Sender.html"><code>Sender</code></a> handles are clone-able, allowing concurrent send and |
| receive actions. <a href="struct.Sender.html"><code>Sender</code></a> and <a href="struct.Receiver.html"><code>Receiver</code></a> are both <code>Send</code> and <code>Sync</code> as |
| long as <code>T</code> is also <code>Send</code> or <code>Sync</code> respectively.</p> |
| <p>When a value is sent, <strong>all</strong> <a href="struct.Receiver.html"><code>Receiver</code></a> handles are notified and will |
| receive the value. The value is stored once inside the channel and cloned on |
| demand for each receiver. Once all receivers have received a clone of the |
| value, the value is released from the channel.</p> |
| <p>A channel is created by calling <a href="fn.channel.html"><code>channel</code></a>, specifying the maximum number |
| of messages the channel can retain at any given time.</p> |
| <p>New <a href="struct.Receiver.html"><code>Receiver</code></a> handles are created by calling <a href="struct.Sender.html#method.subscribe"><code>Sender::subscribe</code></a>. The |
| returned <a href="struct.Receiver.html"><code>Receiver</code></a> will receive values sent <strong>after</strong> the call to |
| <code>subscribe</code>.</p> |
| <p>This channel is also suitable for the single-producer multi-consumer |
| use-case, where a single sender broadcasts values to many receivers.</p> |
| <h3 id="lagging"><a href="#lagging">Lagging</a></h3> |
| <p>As sent messages must be retained until <strong>all</strong> <a href="struct.Receiver.html"><code>Receiver</code></a> handles receive |
| a clone, broadcast channels are susceptible to the “slow receiver” problem. |
| In this case, all but one receiver are able to receive values at the rate |
| they are sent. Because one receiver is stalled, the channel starts to fill |
| up.</p> |
| <p>This broadcast channel implementation handles this case by setting a hard |
| upper bound on the number of values the channel may retain at any given |
| time. This upper bound is passed to the <a href="fn.channel.html"><code>channel</code></a> function as an argument.</p> |
| <p>If a value is sent when the channel is at capacity, the oldest value |
| currently held by the channel is released. This frees up space for the new |
| value. Any receiver that has not yet seen the released value will return |
| <a href="error/enum.RecvError.html#variant.Lagged"><code>RecvError::Lagged</code></a> the next time <a href="struct.Receiver.html#method.recv"><code>recv</code></a> is called.</p> |
| <p>Once <a href="error/enum.RecvError.html#variant.Lagged"><code>RecvError::Lagged</code></a> is returned, the lagging receiver’s position is |
| updated to the oldest value contained by the channel. The next call to |
| <a href="struct.Receiver.html#method.recv"><code>recv</code></a> will return this value.</p> |
| <p>This behavior enables a receiver to detect when it has lagged so far behind |
| that data has been dropped. The caller may decide how to respond to this: |
| either by aborting its task or by tolerating lost messages and resuming |
| consumption of the channel.</p> |
| <h3 id="closing"><a href="#closing">Closing</a></h3> |
| <p>When <strong>all</strong> <a href="struct.Sender.html"><code>Sender</code></a> handles have been dropped, no new values may be |
| sent. At this point, the channel is “closed”. Once a receiver has received |
| all values retained by the channel, the next call to <a href="struct.Receiver.html#method.recv"><code>recv</code></a> will return |
| with <a href="error/enum.RecvError.html#variant.Closed"><code>RecvError::Closed</code></a>.</p> |
| <h2 id="examples"><a href="#examples">Examples</a></h2> |
| <p>Basic usage</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::sync::broadcast; |
| |
| <span class="attribute">#[tokio::main] |
| </span><span class="kw">async fn </span>main() { |
| <span class="kw">let </span>(tx, <span class="kw-2">mut </span>rx1) = broadcast::channel(<span class="number">16</span>); |
| <span class="kw">let </span><span class="kw-2">mut </span>rx2 = tx.subscribe(); |
| |
| tokio::spawn(<span class="kw">async move </span>{ |
| <span class="macro">assert_eq!</span>(rx1.recv().<span class="kw">await</span>.unwrap(), <span class="number">10</span>); |
| <span class="macro">assert_eq!</span>(rx1.recv().<span class="kw">await</span>.unwrap(), <span class="number">20</span>); |
| }); |
| |
| tokio::spawn(<span class="kw">async move </span>{ |
| <span class="macro">assert_eq!</span>(rx2.recv().<span class="kw">await</span>.unwrap(), <span class="number">10</span>); |
| <span class="macro">assert_eq!</span>(rx2.recv().<span class="kw">await</span>.unwrap(), <span class="number">20</span>); |
| }); |
| |
| tx.send(<span class="number">10</span>).unwrap(); |
| tx.send(<span class="number">20</span>).unwrap(); |
| }</code></pre></div> |
| <p>Handling lag</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::sync::broadcast; |
| |
| <span class="attribute">#[tokio::main] |
| </span><span class="kw">async fn </span>main() { |
| <span class="kw">let </span>(tx, <span class="kw-2">mut </span>rx) = broadcast::channel(<span class="number">2</span>); |
| |
| tx.send(<span class="number">10</span>).unwrap(); |
| tx.send(<span class="number">20</span>).unwrap(); |
| tx.send(<span class="number">30</span>).unwrap(); |
| |
| <span class="comment">// The receiver lagged behind |
| </span><span class="macro">assert!</span>(rx.recv().<span class="kw">await</span>.is_err()); |
| |
| <span class="comment">// At this point, we can abort or continue with lost messages |
| |
| </span><span class="macro">assert_eq!</span>(<span class="number">20</span>, rx.recv().<span class="kw">await</span>.unwrap()); |
| <span class="macro">assert_eq!</span>(<span class="number">30</span>, rx.recv().<span class="kw">await</span>.unwrap()); |
| }</code></pre></div> |
| </div></details><h2 id="modules" class="small-section-header"><a href="#modules">Modules</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="mod" href="error/index.html" title="tokio::sync::broadcast::error mod">error</a></div><div class="item-right docblock-short">Broadcast error types</div></div></div><h2 id="structs" class="small-section-header"><a href="#structs">Structs</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Receiver.html" title="tokio::sync::broadcast::Receiver struct">Receiver</a></div><div class="item-right docblock-short">Receiving-half of the <a href="index.html"><code>broadcast</code></a> channel.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Sender.html" title="tokio::sync::broadcast::Sender struct">Sender</a></div><div class="item-right docblock-short">Sending-half of the <a href="index.html"><code>broadcast</code></a> channel.</div></div></div><h2 id="functions" class="small-section-header"><a href="#functions">Functions</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.channel.html" title="tokio::sync::broadcast::channel fn">channel</a></div><div class="item-right docblock-short">Create a bounded, multi-producer, multi-consumer channel where each sent |
| value is broadcasted to all active receivers.</div></div></div></section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="tokio" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
