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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="Dispatches trace events to `Subscriber`s."><title>tracing_core::dispatcher - 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="tracing_core" 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="icon" href="https://raw.githubusercontent.com/tokio-rs/tracing/main/assets/favicon.ico"></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 dispatcher</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><a class="logo-container" href="../../tracing_core/index.html"><img src="https://raw.githubusercontent.com/tokio-rs/tracing/main/assets/logo-type.png" alt="logo"></a><h2><a href="../../tracing_core/index.html">tracing_<wbr>core</a><span class="version">0.1.36</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">Module dispatcher</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#using-the-trace-dispatcher" title="Using the Trace Dispatcher">Using the Trace Dispatcher</a><ul><li><a href="#setting-the-default-subscriber" title="Setting the Default Subscriber">Setting the Default Subscriber</a></li><li><a href="#accessing-the-default-subscriber" title="Accessing the Default Subscriber">Accessing the Default Subscriber</a></li></ul></li></ul><h3><a href="#structs">Module Items</a></h3><ul class="block"><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 class="in-crate"><a href="../index.html">In crate tracing_<wbr>core</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">tracing_core</a></div><h1>Module <span>dispatcher</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/tracing_core/dispatcher.rs.html#1-1067">Source</a> </span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Dispatches trace events to <a href="../trait.Subscriber.html" title="trait tracing_core::Subscriber"><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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<h2 id="using-the-trace-dispatcher"><a class="doc-anchor" href="#using-the-trace-dispatcher">§</a>Using the Trace Dispatcher</h2>
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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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<h3 id="setting-the-default-subscriber"><a class="doc-anchor" href="#setting-the-default-subscriber">§</a>Setting the Default Subscriber</h3>
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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" title="fn tracing_core::dispatcher::with_default"><code>with_default</code></a> and
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<a href="fn.set_global_default.html" title="fn tracing_core::dispatcher::set_global_default"><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" title="struct tracing_core::Dispatch"><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"><code><span class="kw">use </span>dispatcher::Dispatch;
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<span class="kw">let </span>my_subscriber = FooSubscriber::new();
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<span class="kw">let </span>my_dispatch = Dispatch::new(my_subscriber);</code></pre></div>
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<p>Then, we can use <a href="fn.with_default.html" title="fn tracing_core::dispatcher::with_default"><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"><code><span class="comment">// no default subscriber
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</span>dispatcher::with_default(<span class="kw-2">&</span>my_dispatch, || {
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<span class="comment">// my_subscriber is the default
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</span>});
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<span class="comment">// no default subscriber again</span></code></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" title="fn tracing_core::dispatcher::set_global_default"><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"><code><span class="comment">// no default subscriber
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</span>dispatcher::set_global_default(my_dispatch)
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<span class="comment">// `set_global_default` will return an error if the global default
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// subscriber has already been set.
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</span>.expect(<span class="string">"global default was already set!"</span>);
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<span class="comment">// `my_subscriber` is now the default</span></code></pre></div><pre class="ignore" style="white-space:normal;font:inherit;">
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<strong>Note</strong>:the thread-local scoped dispatcher
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(<a href="#fn.with_default"><code>with_default</code></a>) requires the
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Rust standard library. <code>no_std</code> users should use
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<a href="#fn.set_global_default"><code>set_global_default</code></a>
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instead.
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</pre>
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<h3 id="accessing-the-default-subscriber"><a class="doc-anchor" href="#accessing-the-default-subscriber">§</a>Accessing the Default Subscriber</h3>
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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" title="fn tracing_core::dispatcher::get_default"><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></details><h2 id="structs" class="section-header">Structs<a href="#structs" class="anchor">§</a></h2><dl class="item-table"><dt><a class="struct" href="struct.DefaultGuard.html" title="struct tracing_core::dispatcher::DefaultGuard">Default<wbr>Guard</a></dt><dd>A guard that resets the current default dispatcher to the prior
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default dispatcher when dropped.</dd><dt><a class="struct" href="struct.Dispatch.html" title="struct tracing_core::dispatcher::Dispatch">Dispatch</a></dt><dd><code>Dispatch</code> trace data to a <a href="../trait.Subscriber.html" title="trait tracing_core::Subscriber"><code>Subscriber</code></a>.</dd><dt><a class="struct" href="struct.SetGlobalDefaultError.html" title="struct tracing_core::dispatcher::SetGlobalDefaultError">SetGlobal<wbr>Default<wbr>Error</a></dt><dd>Returned if setting the global dispatcher fails.</dd><dt><a class="struct" href="struct.WeakDispatch.html" title="struct tracing_core::dispatcher::WeakDispatch">Weak<wbr>Dispatch</a></dt><dd><code>WeakDispatch</code> is a version of <a href="../struct.Dispatch.html" title="struct tracing_core::Dispatch"><code>Dispatch</code></a> that holds a non-owning reference
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to a <a href="../trait.Subscriber.html" title="trait tracing_core::Subscriber"><code>Subscriber</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.get_default.html" title="fn tracing_core::dispatcher::get_default">get_<wbr>default</a></dt><dd>Executes a closure with a reference to this thread’s current <a href="../struct.Dispatch.html" title="struct tracing_core::Dispatch">dispatcher</a>.</dd><dt><a class="fn" href="fn.set_default.html" title="fn tracing_core::dispatcher::set_default">set_<wbr>default</a></dt><dd>Sets the dispatch as the default dispatch for the duration of the lifetime
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of the returned DefaultGuard</dd><dt><a class="fn" href="fn.set_global_default.html" title="fn tracing_core::dispatcher::set_global_default">set_<wbr>global_<wbr>default</a></dt><dd>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>.)</dd><dt><a class="fn" href="fn.with_default.html" title="fn tracing_core::dispatcher::with_default">with_<wbr>default</a></dt><dd>Sets this dispatch as the default for the duration of a closure.</dd></dl></section></div></main></body></html> |