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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 `dispatcher` mod in crate `tracing`."><meta name="keywords" content="rust, rustlang, rust-lang, dispatcher"><title>tracing::dispatcher - 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='../../tracing/index.html'><div class='logo-container'><img src='https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png' alt='logo'></div></a><p class="location">Module dispatcher</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#structs">Structs</a></li><li><a href="#functions">Functions</a></li></ul></div><p class="location"><a href="../index.html">tracing</a></p><div id="sidebar-vars" data-name="dispatcher" 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">tracing</a>::<wbr><a class="mod" href="">dispatcher</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/tracing/dispatcher.rs.html#1-152" title="goto source code">[src]</a></span></h1><div class="docblock"><p>Dispatches trace events to <a href="struct.Subscriber.html"><code>Subscriber</code></a>s.</p>
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<p>The <em>dispatcher</em> is the component of the tracing system which is responsible
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for forwarding trace data from the instrumentation points that generate it
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to the subscriber that collects it.</p>
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<h1 id="using-the-trace-dispatcher" class="section-header"><a href="#using-the-trace-dispatcher">Using the Trace Dispatcher</a></h1>
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<p>Every thread in a program using <code>tracing</code> has a <em>default subscriber</em>. When
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events occur, or spans are created, they are dispatched to the thread's
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current subscriber.</p>
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<h2 id="setting-the-default-subscriber" class="section-header"><a href="#setting-the-default-subscriber">Setting the Default Subscriber</a></h2>
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<p>By default, the current subscriber is an empty implementation that does
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nothing. To use a subscriber implementation, it must be set as the default.
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There are two methods for doing so: <a href="fn.with_default.html"><code>with_default</code></a> and
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<a href="fn.set_global_default.html"><code>set_global_default</code></a>. <code>with_default</code> sets the default subscriber for the
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duration of a scope, while <code>set_global_default</code> sets a default subscriber
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for the entire process.</p>
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<p>To use either of these functions, we must first wrap our subscriber in a
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<a href="struct.Dispatch.html"><code>Dispatch</code></a>, a cloneable, type-erased reference to a subscriber. For
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example:</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">dispatcher</span>::<span class="ident">Dispatch</span>;
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<span class="kw">let</span> <span class="ident">my_subscriber</span> <span class="op">=</span> <span class="ident">FooSubscriber</span>::<span class="ident">new</span>();
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<span class="kw">let</span> <span class="ident">my_dispatch</span> <span class="op">=</span> <span class="ident">Dispatch</span>::<span class="ident">new</span>(<span class="ident">my_subscriber</span>);</pre></div>
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<p>Then, we can use <a href="fn.with_default.html"><code>with_default</code></a> to set our <code>Dispatch</code> as the default for
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the duration of a block:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="comment">// no default subscriber</span>
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<span class="ident">dispatcher</span>::<span class="ident">with_default</span>(<span class="kw-2">&</span><span class="ident">my_dispatch</span>, <span class="op">|</span><span class="op">|</span> {
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<span class="comment">// my_subscriber is the default</span>
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});
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<span class="comment">// no default subscriber again</span></pre></div>
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<p>It's important to note that <code>with_default</code> will not propagate the current
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thread's default subscriber to any threads spawned within the <code>with_default</code>
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block. To propagate the default subscriber to new threads, either use
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<code>with_default</code> from the new thread, or use <code>set_global_default</code>.</p>
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<p>As an alternative to <code>with_default</code>, we can use <a href="fn.set_global_default.html"><code>set_global_default</code></a> to
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set a <code>Dispatch</code> as the default for all threads, for the lifetime of the
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program. For example:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="comment">// no default subscriber</span>
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<span class="ident">dispatcher</span>::<span class="ident">set_global_default</span>(<span class="ident">my_dispatch</span>)
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<span class="comment">// `set_global_default` will return an error if the global default</span>
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<span class="comment">// subscriber has already been set.</span>
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.<span class="ident">expect</span>(<span class="string">"global default was already set!"</span>);
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<span class="comment">// `my_subscriber` is now the default</span></pre></div>
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<div class="information">
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<div class="tooltip ignore" style="">ⓘ<span class="tooltiptext">Note</span></div>
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</div>
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<div class="example-wrap" style="display:inline-block">
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<pre class="ignore" style="white-space:normal;font:inherit;">
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<strong>Note</strong>: The thread-local scoped dispatcher (<code>with_default</code>)
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requires the Rust standard library. <code>no_std</code> users should
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use <a href="fn.set_global_default.html"><code>set_global_default</code></a>
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instead.
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</pre></div>
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<h2 id="accessing-the-default-subscriber" class="section-header"><a href="#accessing-the-default-subscriber">Accessing the Default Subscriber</a></h2>
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<p>A thread's current default subscriber can be accessed using the
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<a href="fn.get_default.html"><code>get_default</code></a> function, which executes a closure with a reference to the
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currently default <code>Dispatch</code>. This is used primarily by <code>tracing</code>
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instrumentation.</p>
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</div><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.DefaultGuard.html" title="tracing::dispatcher::DefaultGuard struct">DefaultGuard</a></td><td class="docblock-short"><p>A guard that resets the current default dispatcher to the prior
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default dispatcher when dropped.</p>
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</td></tr><tr class="module-item"><td><a class="struct" href="struct.Dispatch.html" title="tracing::dispatcher::Dispatch struct">Dispatch</a></td><td class="docblock-short"><p><code>Dispatch</code> trace data to a <a href="trait.Subscriber.html"><code>Subscriber</code></a>.</p>
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</td></tr><tr class="module-item"><td><a class="struct" href="struct.SetGlobalDefaultError.html" title="tracing::dispatcher::SetGlobalDefaultError struct">SetGlobalDefaultError</a></td><td class="docblock-short"><p>Returned if setting the global dispatcher fails.</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.get_default.html" title="tracing::dispatcher::get_default fn">get_default</a></td><td class="docblock-short"><p>Executes a closure with a reference to this thread's current <a href="../dispatcher/struct.Dispatch.html">dispatcher</a>.</p>
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</td></tr><tr class="module-item"><td><a class="fn" href="fn.set_default.html" title="tracing::dispatcher::set_default fn">set_default</a></td><td class="docblock-short"><p>Sets the dispatch as the default dispatch for the duration of the lifetime
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of the returned DefaultGuard</p>
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</td></tr><tr class="module-item"><td><a class="fn" href="fn.set_global_default.html" title="tracing::dispatcher::set_global_default fn">set_global_default</a></td><td class="docblock-short"><p>Sets this dispatch as the global default for the duration of the entire program.
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Will be used as a fallback if no thread-local dispatch has been set in a thread
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(using <code>with_default</code>.)</p>
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</td></tr><tr class="module-item"><td><a class="fn" href="fn.with_default.html" title="tracing::dispatcher::with_default fn">with_default</a></td><td class="docblock-short"><p>Sets this dispatch as the default for the duration of a closure.</p>
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</td></tr></table></section><section id="search" class="content hidden"></section><section class="footer"></section><div id="rustdoc-vars" data-root-path="../../" data-current-crate="tracing"></div>
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