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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 `broadcast` mod in crate `tokio`."><meta name="keywords" content="rust, rustlang, rust-lang, broadcast"><title>tokio::sync::broadcast - 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="../../../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../../../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../../../ayu.css" disabled ><script id="default-settings"></script><script src="../../../storage.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../../../favicon.svg">
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<link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><style type="text/css">#crate-search{background-image:url("../../../down-arrow.svg");}</style></head><body class="rustdoc mod"><!--[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='../../../tokio/index.html'><div class='logo-container rust-logo'><img src='../../../rust-logo.png' alt='logo'></div></a><p class="location">Module broadcast</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li><li><a href="#functions">Functions</a></li></ul></div><p class="location"><a href="../../index.html">tokio</a>::<wbr><a href="../index.html">sync</a></p><script>window.sidebarCurrent = {name: "broadcast", ty: "mod", relpath: "../"};</script><script defer src="../sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu"><img src="../../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices" role="menu"></div></div><script src="../../../theme.js"></script><nav class="sub"><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" disabled autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" class="help-button">?</button>
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<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/tokio/sync/broadcast.rs.html#1-1071" title="goto source code">[src]</a></span><span class="in-band">Module <a href="../../index.html">tokio</a>::<wbr><a href="../index.html">sync</a>::<wbr><a class="mod" href="">broadcast</a></span></h1><div class="docblock"><p>A multi-producer, multi-consumer broadcast queue. Each sent value is seen by
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all consumers.</p>
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<p>A <a href="../../../tokio/sync/broadcast/struct.Sender.html"><code>Sender</code></a> is used to broadcast values to <strong>all</strong> connected <a href="../../../tokio/sync/broadcast/struct.Receiver.html"><code>Receiver</code></a>
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values. <a href="../../../tokio/sync/broadcast/struct.Sender.html"><code>Sender</code></a> handles are clone-able, allowing concurrent send and
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receive actions. <a href="../../../tokio/sync/broadcast/struct.Sender.html"><code>Sender</code></a> and <a href="../../../tokio/sync/broadcast/struct.Receiver.html"><code>Receiver</code></a> are both <code>Send</code> and <code>Sync</code> as
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long as <code>T</code> is also <code>Send</code> or <code>Sync</code> respectively.</p>
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<p>When a value is sent, <strong>all</strong> <a href="../../../tokio/sync/broadcast/struct.Receiver.html"><code>Receiver</code></a> handles are notified and will
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receive the value. The value is stored once inside the channel and cloned on
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demand for each receiver. Once all receivers have received a clone of the
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value, the value is released from the channel.</p>
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<p>A channel is created by calling <a href="../../../tokio/sync/broadcast/fn.channel.html"><code>channel</code></a>, specifying the maximum number
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of messages the channel can retain at any given time.</p>
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<p>New <a href="../../../tokio/sync/broadcast/struct.Receiver.html"><code>Receiver</code></a> handles are created by calling <a href="../../../tokio/sync/broadcast/struct.Sender.html#method.subscribe"><code>Sender::subscribe</code></a>. The
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returned <a href="../../../tokio/sync/broadcast/struct.Receiver.html"><code>Receiver</code></a> will receive values sent <strong>after</strong> the call to
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<code>subscribe</code>.</p>
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<h2 id="lagging" class="section-header"><a href="#lagging">Lagging</a></h2>
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<p>As sent messages must be retained until <strong>all</strong> <a href="../../../tokio/sync/broadcast/struct.Receiver.html"><code>Receiver</code></a> handles receive
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a clone, broadcast channels are susceptible to the "slow receiver" problem.
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In this case, all but one receiver are able to receive values at the rate
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they are sent. Because one receiver is stalled, the channel starts to fill
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up.</p>
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<p>This broadcast channel implementation handles this case by setting a hard
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upper bound on the number of values the channel may retain at any given
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time. This upper bound is passed to the <a href="../../../tokio/sync/broadcast/fn.channel.html"><code>channel</code></a> function as an argument.</p>
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<p>If a value is sent when the channel is at capacity, the oldest value
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currently held by the channel is released. This frees up space for the new
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value. Any receiver that has not yet seen the released value will return
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<a href="../../../tokio/sync/broadcast/error/enum.RecvError.html#variant.Lagged"><code>RecvError::Lagged</code></a> the next time <a href="../../../tokio/sync/broadcast/struct.Receiver.html#method.recv"><code>recv</code></a> is called.</p>
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<p>Once <a href="../../../tokio/sync/broadcast/error/enum.RecvError.html#variant.Lagged"><code>RecvError::Lagged</code></a> is returned, the lagging receiver's position is
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updated to the oldest value contained by the channel. The next call to
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<a href="../../../tokio/sync/broadcast/struct.Receiver.html#method.recv"><code>recv</code></a> will return this value.</p>
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<p>This behavior enables a receiver to detect when it has lagged so far behind
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that data has been dropped. The caller may decide how to respond to this:
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either by aborting its task or by tolerating lost messages and resuming
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consumption of the channel.</p>
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<h2 id="closing" class="section-header"><a href="#closing">Closing</a></h2>
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<p>When <strong>all</strong> <a href="../../../tokio/sync/broadcast/struct.Sender.html"><code>Sender</code></a> handles have been dropped, no new values may be
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sent. At this point, the channel is "closed". Once a receiver has received
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all values retained by the channel, the next call to <a href="../../../tokio/sync/broadcast/struct.Receiver.html#method.recv"><code>recv</code></a> will return
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with <a href="../../../tokio/sync/broadcast/error/enum.RecvError.html#variant.Closed"><code>RecvError::Closed</code></a>.</p>
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<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
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<p>Basic usage</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">tokio</span>::<span class="ident">sync</span>::<span class="ident">broadcast</span>;
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<span class="attribute">#[<span class="ident">tokio</span>::<span class="ident">main</span>]</span>
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<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="kw">let</span> (<span class="ident">tx</span>, <span class="kw-2">mut</span> <span class="ident">rx1</span>) <span class="op">=</span> <span class="ident">broadcast</span>::<span class="ident">channel</span>(<span class="number">16</span>);
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">rx2</span> <span class="op">=</span> <span class="ident">tx</span>.<span class="ident">subscribe</span>();
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<span class="ident">tokio</span>::<span class="ident">spawn</span>(<span class="kw">async</span> <span class="kw">move</span> {
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">rx1</span>.<span class="ident">recv</span>().<span class="kw">await</span>.<span class="ident">unwrap</span>(), <span class="number">10</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">rx1</span>.<span class="ident">recv</span>().<span class="kw">await</span>.<span class="ident">unwrap</span>(), <span class="number">20</span>);
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});
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<span class="ident">tokio</span>::<span class="ident">spawn</span>(<span class="kw">async</span> <span class="kw">move</span> {
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">rx2</span>.<span class="ident">recv</span>().<span class="kw">await</span>.<span class="ident">unwrap</span>(), <span class="number">10</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">rx2</span>.<span class="ident">recv</span>().<span class="kw">await</span>.<span class="ident">unwrap</span>(), <span class="number">20</span>);
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});
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<span class="ident">tx</span>.<span class="ident">send</span>(<span class="number">10</span>).<span class="ident">unwrap</span>();
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<span class="ident">tx</span>.<span class="ident">send</span>(<span class="number">20</span>).<span class="ident">unwrap</span>();
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}</pre></div>
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<p>Handling lag</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">tokio</span>::<span class="ident">sync</span>::<span class="ident">broadcast</span>;
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<span class="attribute">#[<span class="ident">tokio</span>::<span class="ident">main</span>]</span>
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<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="kw">let</span> (<span class="ident">tx</span>, <span class="kw-2">mut</span> <span class="ident">rx</span>) <span class="op">=</span> <span class="ident">broadcast</span>::<span class="ident">channel</span>(<span class="number">2</span>);
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<span class="ident">tx</span>.<span class="ident">send</span>(<span class="number">10</span>).<span class="ident">unwrap</span>();
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<span class="ident">tx</span>.<span class="ident">send</span>(<span class="number">20</span>).<span class="ident">unwrap</span>();
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<span class="ident">tx</span>.<span class="ident">send</span>(<span class="number">30</span>).<span class="ident">unwrap</span>();
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<span class="comment">// The receiver lagged behind</span>
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<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">rx</span>.<span class="ident">recv</span>().<span class="kw">await</span>.<span class="ident">is_err</span>());
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<span class="comment">// At this point, we can abort or continue with lost messages</span>
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">20</span>, <span class="ident">rx</span>.<span class="ident">recv</span>().<span class="kw">await</span>.<span class="ident">unwrap</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">30</span>, <span class="ident">rx</span>.<span class="ident">recv</span>().<span class="kw">await</span>.<span class="ident">unwrap</span>());
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}</pre></div>
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</div><h2 id="modules" class="section-header"><a href="#modules">Modules</a></h2>
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<table><tr class="module-item"><td><a class="mod" href="error/index.html" title="tokio::sync::broadcast::error mod">error</a></td><td class="docblock-short"><p>Broadcast error types</p>
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</td></tr></table><h2 id="structs" class="section-header"><a href="#structs">Structs</a></h2>
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<table><tr class="module-item"><td><a class="struct" href="struct.Receiver.html" title="tokio::sync::broadcast::Receiver struct">Receiver</a></td><td class="docblock-short"><p>Receiving-half of the <a href="../../../tokio/sync/broadcast/index.html"><code>broadcast</code></a> channel.</p>
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</td></tr><tr class="module-item"><td><a class="struct" href="struct.Sender.html" title="tokio::sync::broadcast::Sender struct">Sender</a></td><td class="docblock-short"><p>Sending-half of the <a href="../../../tokio/sync/broadcast/index.html"><code>broadcast</code></a> channel.</p>
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</td></tr></table><h2 id="functions" class="section-header"><a href="#functions">Functions</a></h2>
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<table><tr class="module-item"><td><a class="fn" href="fn.channel.html" title="tokio::sync::broadcast::channel fn">channel</a></td><td class="docblock-short"><p>Create a bounded, multi-producer, multi-consumer channel where each sent
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value is broadcasted to all active receivers.</p>
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</td></tr></table></section><section id="search" class="content hidden"></section><section class="footer"></section><script>window.rootPath = "../../../";window.currentCrate = "tokio";</script><script src="../../../main.js"></script><script defer src="../../../search-index.js"></script></body></html> |