| <!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."><meta name="keywords" content="rust, rustlang, rust-lang, dispatcher"><title>tracing_core::dispatcher - 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="../../tracing_core/index.html"><div class="logo-container"><img src="https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../tracing_core/index.html"><div class="logo-container"> |
| <img src="https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png" alt="logo"></div></a><h2 class="location"><a href="#">Module dispatcher</a></h2><div class="sidebar-elems"><section><ul class="block"><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">tracing_core</a>::<wbr><a class="mod" href="#">dispatcher</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/tracing_core/dispatcher.rs.html#1-1071">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>Dispatches trace events to <a href="../trait.Subscriber.html" title="Subscriber"><code>Subscriber</code></a>s.</p> |
| <p>The <em>dispatcher</em> is the component of the tracing system which is responsible |
| for forwarding trace data from the instrumentation points that generate it |
| to the subscriber that collects it.</p> |
| <h2 id="using-the-trace-dispatcher"><a href="#using-the-trace-dispatcher">Using the Trace Dispatcher</a></h2> |
| <p>Every thread in a program using <code>tracing</code> has a <em>default subscriber</em>. When |
| events occur, or spans are created, they are dispatched to the thread’s |
| current subscriber.</p> |
| <h3 id="setting-the-default-subscriber"><a href="#setting-the-default-subscriber">Setting the Default Subscriber</a></h3> |
| <p>By default, the current subscriber is an empty implementation that does |
| nothing. To use a subscriber implementation, it must be set as the default. |
| There are two methods for doing so: <a href="fn.with_default.html" title="with_default"><code>with_default</code></a> and |
| <a href="fn.set_global_default.html" title="set_global_default"><code>set_global_default</code></a>. <code>with_default</code> sets the default subscriber for the |
| duration of a scope, while <code>set_global_default</code> sets a default subscriber |
| for the entire process.</p> |
| <p>To use either of these functions, we must first wrap our subscriber in a |
| <a href="../struct.Dispatch.html" title="Dispatch"><code>Dispatch</code></a>, a cloneable, type-erased reference to a subscriber. For |
| example:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>dispatcher::Dispatch; |
| |
| <span class="kw">let </span>my_subscriber = FooSubscriber::new(); |
| <span class="kw">let </span>my_dispatch = Dispatch::new(my_subscriber);</code></pre></div> |
| <p>Then, we can use <a href="fn.with_default.html" title="with_default"><code>with_default</code></a> to set our <code>Dispatch</code> as the default for |
| the duration of a block:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="comment">// no default subscriber |
| |
| </span>dispatcher::with_default(<span class="kw-2">&</span>my_dispatch, || { |
| <span class="comment">// my_subscriber is the default |
| </span>}); |
| |
| <span class="comment">// no default subscriber again</span></code></pre></div> |
| <p>It’s important to note that <code>with_default</code> will not propagate the current |
| thread’s default subscriber to any threads spawned within the <code>with_default</code> |
| block. To propagate the default subscriber to new threads, either use |
| <code>with_default</code> from the new thread, or use <code>set_global_default</code>.</p> |
| <p>As an alternative to <code>with_default</code>, we can use <a href="fn.set_global_default.html" title="set_global_default"><code>set_global_default</code></a> to |
| set a <code>Dispatch</code> as the default for all threads, for the lifetime of the |
| program. For example:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="comment">// no default subscriber |
| |
| </span>dispatcher::set_global_default(my_dispatch) |
| <span class="comment">// `set_global_default` will return an error if the global default |
| // subscriber has already been set. |
| </span>.expect(<span class="string">"global default was already set!"</span>); |
| |
| <span class="comment">// `my_subscriber` is now the default</span></code></pre></div> |
| <pre class="ignore" style="white-space:normal;font:inherit;"> |
| <strong>Note</strong>:the thread-local scoped dispatcher |
| (<a href="#fn.with_default"><code>with_default</code></a>) requires the |
| Rust standard library. <code>no_std</code> users should use |
| <a href="#fn.set_global_default"><code>set_global_default</code></a> |
| instead. |
| </pre> |
| <h3 id="accessing-the-default-subscriber"><a href="#accessing-the-default-subscriber">Accessing the Default Subscriber</a></h3> |
| <p>A thread’s current default subscriber can be accessed using the |
| <a href="fn.get_default.html" title="get_default"><code>get_default</code></a> function, which executes a closure with a reference to the |
| currently default <code>Dispatch</code>. This is used primarily by <code>tracing</code> |
| instrumentation.</p> |
| </div></details><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.DefaultGuard.html" title="tracing_core::dispatcher::DefaultGuard struct">DefaultGuard</a></div><div class="item-right docblock-short">A guard that resets the current default dispatcher to the prior |
| default dispatcher when dropped.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Dispatch.html" title="tracing_core::dispatcher::Dispatch struct">Dispatch</a></div><div class="item-right docblock-short"><code>Dispatch</code> trace data to a <a href="../trait.Subscriber.html" title="Subscriber"><code>Subscriber</code></a>.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.SetGlobalDefaultError.html" title="tracing_core::dispatcher::SetGlobalDefaultError struct">SetGlobalDefaultError</a></div><div class="item-right docblock-short">Returned if setting the global dispatcher fails.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.WeakDispatch.html" title="tracing_core::dispatcher::WeakDispatch struct">WeakDispatch</a></div><div class="item-right docblock-short"><code>WeakDispatch</code> is a version of <a href="../struct.Dispatch.html" title="Dispatch"><code>Dispatch</code></a> that holds a non-owning reference |
| to a <a href="../trait.Subscriber.html" title="Subscriber"><code>Subscriber</code></a>.</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.get_default.html" title="tracing_core::dispatcher::get_default fn">get_default</a></div><div class="item-right docblock-short">Executes a closure with a reference to this thread’s current <a href="../struct.Dispatch.html">dispatcher</a>.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.set_default.html" title="tracing_core::dispatcher::set_default fn">set_default</a></div><div class="item-right docblock-short">Sets the dispatch as the default dispatch for the duration of the lifetime |
| of the returned DefaultGuard</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.set_global_default.html" title="tracing_core::dispatcher::set_global_default fn">set_global_default</a></div><div class="item-right docblock-short">Sets this dispatch as the global default for the duration of the entire program. |
| Will be used as a fallback if no thread-local dispatch has been set in a thread |
| (using <code>with_default</code>.)</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.with_default.html" title="tracing_core::dispatcher::with_default fn">with_default</a></div><div class="item-right docblock-short">Sets this dispatch as the default for the duration of a closure.</div></div></div></section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="tracing_core" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
