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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 `watch` mod in crate `tokio`."><meta name="keywords" content="rust, rustlang, rust-lang, watch"><title>tokio::sync::watch - 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 watch</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><div id="sidebar-vars" data-name="watch" data-ty="mod" data-relpath="../"></div><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="in-band">Module <a href="../../index.html">tokio</a>::<wbr><a href="../index.html">sync</a>::<wbr><a class="mod" href="">watch</a></span><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/watch.rs.html#1-518" title="goto source code">[src]</a></span></h1><div class="docblock"><p>A single-producer, multi-consumer channel that only retains the <em>last</em> sent
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value.</p>
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<p>This channel is useful for watching for changes to a value from multiple
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points in the code base, for example, changes to configuration values.</p>
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<h1 id="usage" class="section-header"><a href="#usage">Usage</a></h1>
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<p><a href="../../../tokio/sync/watch/fn.channel.html"><code>channel</code></a> returns a <a href="../../../tokio/sync/watch/struct.Sender.html"><code>Sender</code></a> / <a href="../../../tokio/sync/watch/struct.Receiver.html"><code>Receiver</code></a> pair. These are the producer
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and sender halves of the channel. The channel is created with an initial
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value. The <strong>latest</strong> value stored in the channel is accessed with
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<a href="../../../tokio/sync/watch/struct.Receiver.html#method.borrow"><code>Receiver::borrow()</code></a>. Awaiting <a href="../../../tokio/sync/watch/struct.Receiver.html#method.changed"><code>Receiver::changed()</code></a> waits for a new
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value to sent by the <a href="../../../tokio/sync/watch/struct.Sender.html"><code>Sender</code></a> half.</p>
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<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
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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">watch</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">watch</span>::<span class="ident">channel</span>(<span class="string">"hello"</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="kw">while</span> <span class="ident">rx</span>.<span class="ident">changed</span>().<span class="kw">await</span>.<span class="ident">is_ok</span>() {
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"received = {:?}"</span>, <span class="kw-2">*</span><span class="ident">rx</span>.<span class="ident">borrow</span>());
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}
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});
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<span class="ident">tx</span>.<span class="ident">send</span>(<span class="string">"world"</span>)<span class="question-mark">?</span>;</pre></div>
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<h1 id="closing" class="section-header"><a href="#closing">Closing</a></h1>
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<p><a href="../../../tokio/sync/watch/struct.Sender.html#method.is_closed"><code>Sender::is_closed</code></a> and <a href="../../../tokio/sync/watch/struct.Sender.html#method.closed"><code>Sender::closed</code></a> allow the producer to detect
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when all <a href="../../../tokio/sync/watch/struct.Receiver.html"><code>Receiver</code></a> handles have been dropped. This indicates that there
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is no further interest in the values being produced and work can be stopped.</p>
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<h1 id="thread-safety" class="section-header"><a href="#thread-safety">Thread safety</a></h1>
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<p>Both <a href="../../../tokio/sync/watch/struct.Sender.html"><code>Sender</code></a> and <a href="../../../tokio/sync/watch/struct.Receiver.html"><code>Receiver</code></a> are thread safe. They can be moved to other
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threads and can be used in a concurrent environment. Clones of <a href="../../../tokio/sync/watch/struct.Receiver.html"><code>Receiver</code></a>
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handles may be moved to separate threads and also used concurrently.</p>
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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::watch::error mod">error</a></td><td class="docblock-short"><p>Watch 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::watch::Receiver struct">Receiver</a></td><td class="docblock-short"><p>Receives values from the associated <a href="../../../tokio/sync/watch/struct.Sender.html"><code>Sender</code></a>.</p>
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</td></tr><tr class="module-item"><td><a class="struct" href="struct.Ref.html" title="tokio::sync::watch::Ref struct">Ref</a></td><td class="docblock-short"><p>Returns a reference to the inner value</p>
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</td></tr><tr class="module-item"><td><a class="struct" href="struct.Sender.html" title="tokio::sync::watch::Sender struct">Sender</a></td><td class="docblock-short"><p>Sends values to the associated <a href="../../../tokio/sync/watch/struct.Receiver.html"><code>Receiver</code></a>.</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::watch::channel fn">channel</a></td><td class="docblock-short"><p>Creates a new watch channel, returning the "send" and "receive" handles.</p>
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