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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="Core primitives for `tracing`."><title>tracing_core - 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="../crates.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 crate"><!--[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="#">Crate tracing_core</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"><ul class="block"><li><a id="all-types" href="all.html">All Items</a></li></ul><section id="rustdoc-toc"><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#usage" title="Usage">Usage</a></li><li><a href="#crate-feature-flags" title="Crate Feature Flags">Crate Feature Flags</a><ul><li><a href="#unstable-features" title="Unstable Features">Unstable Features</a></li></ul></li><li><a href="#supported-rust-versions" title="Supported Rust Versions">Supported Rust Versions</a></li></ul><h3><a href="#reexports">Crate Items</a></h3><ul class="block"><li><a href="#reexports" title="Re-exports">Re-exports</a></li><li><a href="#modules" title="Modules">Modules</a></li><li><a href="#macros" title="Macros">Macros</a></li><li><a href="#structs" title="Structs">Structs</a></li><li><a href="#traits" title="Traits">Traits</a></li></ul></section><div id="rustdoc-modnav"></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"><h1>Crate <span>tracing_<wbr>core</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/lib.rs.html#1-311">Source</a> </span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Core primitives for <code>tracing</code>.</p>
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<p><a href="https://crates.io/crates/tracing"><code>tracing</code></a> is a framework for instrumenting Rust programs to collect
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structured, event-based diagnostic information. This crate defines the core
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primitives of <code>tracing</code>.</p>
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<p>This crate provides:</p>
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<ul>
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<li>
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<p><a href="span/struct.Id.html" title="struct tracing_core::span::Id"><code>span::Id</code></a> identifies a span within the execution of a program.</p>
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</li>
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<li>
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<p><a href="struct.Event.html" title="struct tracing_core::Event"><code>Event</code></a> represents a single event within a trace.</p>
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</li>
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<li>
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<p><a href="trait.Subscriber.html" title="trait tracing_core::Subscriber"><code>Subscriber</code></a>, the trait implemented to collect trace data.</p>
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</li>
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<li>
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<p><a href="struct.Metadata.html" title="struct tracing_core::Metadata"><code>Metadata</code></a> and <a href="trait.Callsite.html" title="trait tracing_core::Callsite"><code>Callsite</code></a> provide information describing spans and
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<code>Event</code>s.</p>
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</li>
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<li>
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<p><a href="struct.Field.html" title="struct tracing_core::Field"><code>Field</code></a>, <a href="field/struct.FieldSet.html" title="struct tracing_core::field::FieldSet"><code>FieldSet</code></a>, <a href="field/trait.Value.html" title="trait tracing_core::field::Value"><code>Value</code></a>, and <a href="field/struct.ValueSet.html" title="struct tracing_core::field::ValueSet"><code>ValueSet</code></a> represent the
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structured data attached to a span.</p>
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</li>
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<li>
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<p><a href="struct.Dispatch.html" title="struct tracing_core::Dispatch"><code>Dispatch</code></a> allows spans and events to be dispatched to <code>Subscriber</code>s.</p>
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</li>
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</ul>
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<p>In addition, it defines the global callsite registry and per-thread current
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dispatcher which other components of the tracing system rely on.</p>
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<p><em>Compiler support: <a href="#supported-rust-versions">requires <code>rustc</code> 1.65+</a></em></p>
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<h3 id="usage"><a class="doc-anchor" href="#usage">§</a>Usage</h3>
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<p>Application authors will typically not use this crate directly. Instead,
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they will use the <a href="https://crates.io/crates/tracing"><code>tracing</code></a> crate, which provides a much more
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fully-featured API. However, this crate’s API will change very infrequently,
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so it may be used when dependencies must be very stable.</p>
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<p><code>Subscriber</code> implementations may depend on <code>tracing-core</code> rather than
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<code>tracing</code>, as the additional APIs provided by <code>tracing</code> are primarily useful
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for instrumenting libraries and applications, and are generally not
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necessary for <code>Subscriber</code> implementations.</p>
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<p>The <a href="https://github.com/tokio-rs/tracing"><code>tokio-rs/tracing</code></a> repository contains less stable crates designed to
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be used with the <code>tracing</code> ecosystem. It includes a collection of
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<code>Subscriber</code> implementations, as well as utility and adapter crates.</p>
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<h3 id="crate-feature-flags"><a class="doc-anchor" href="#crate-feature-flags">§</a>Crate Feature Flags</h3>
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<p>The following crate <a href="https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section">feature flags</a> are available:</p>
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<ul>
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<li>
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<p><code>std</code>: Depend on the Rust standard library (enabled by default).</p>
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<p><code>no_std</code> users may disable this feature with <code>default-features = false</code>:</p>
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<div class="example-wrap"><pre class="language-toml"><code>[dependencies]
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tracing-core = { version = "0.1.22", default-features = false }</code></pre></div>
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<p><strong>Note</strong>:<code>tracing-core</code>’s <code>no_std</code> support requires <code>liballoc</code>.</p>
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</li>
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</ul>
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<h4 id="unstable-features"><a class="doc-anchor" href="#unstable-features">§</a>Unstable Features</h4>
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<p>These feature flags enable <strong>unstable</strong> features. The public API may break in 0.1.x
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releases. To enable these features, the <code>--cfg tracing_unstable</code> must be passed to
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<code>rustc</code> when compiling.</p>
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<p>The following unstable feature flags are currently available:</p>
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<ul>
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<li><code>valuable</code>: Enables support for recording <a href="field/index.html" title="mod tracing_core::field">field values</a> using the
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<a href="https://crates.io/crates/valuable"><code>valuable</code></a> crate.</li>
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</ul>
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<h5 id="enabling-unstable-features"><a class="doc-anchor" href="#enabling-unstable-features">§</a>Enabling Unstable Features</h5>
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<p>The easiest way to set the <code>tracing_unstable</code> cfg is to use the <code>RUSTFLAGS</code>
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env variable when running <code>cargo</code> commands:</p>
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<div class="example-wrap"><pre class="language-shell"><code>RUSTFLAGS="--cfg tracing_unstable" cargo build</code></pre></div>
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<p>Alternatively, the following can be added to the <code>.cargo/config</code> file in a
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project to automatically enable the cfg flag for that project:</p>
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<div class="example-wrap"><pre class="language-toml"><code>[build]
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rustflags = ["--cfg", "tracing_unstable"]</code></pre></div><h3 id="supported-rust-versions"><a class="doc-anchor" href="#supported-rust-versions">§</a>Supported Rust Versions</h3>
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<p>Tracing is built against the latest stable release. The minimum supported
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version is 1.65. The current Tracing version is not guaranteed to build on
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Rust versions earlier than the minimum supported version.</p>
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<p>Tracing follows the same compiler support policies as the rest of the Tokio
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project. The current stable Rust compiler and the three most recent minor
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versions before it will always be supported. For example, if the current
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stable compiler version is 1.69, the minimum supported version will not be
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increased past 1.66, three minor versions prior. Increasing the minimum
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supported compiler version is not considered a semver breaking change as
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long as doing so complies with this policy.</p>
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</div></details><h2 id="reexports" class="section-header">Re-exports<a href="#reexports" class="anchor">§</a></h2><dl class="item-table reexports"><dt id="reexport.Kind"><code>pub use self::metadata::<a class="struct" href="metadata/struct.Kind.html" title="struct tracing_core::metadata::Kind">Kind</a>;</code></dt><dt id="reexport.Interest"><code>pub use self::subscriber::<a class="struct" href="subscriber/struct.Interest.html" title="struct tracing_core::subscriber::Interest">Interest</a>;</code></dt></dl><h2 id="modules" class="section-header">Modules<a href="#modules" class="anchor">§</a></h2><dl class="item-table"><dt><a class="mod" href="callsite/index.html" title="mod tracing_core::callsite">callsite</a></dt><dd>Callsites represent the source locations from which spans or events
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originate.</dd><dt><a class="mod" href="dispatcher/index.html" title="mod tracing_core::dispatcher">dispatcher</a></dt><dd>Dispatches trace events to <a href="trait.Subscriber.html" title="trait tracing_core::Subscriber"><code>Subscriber</code></a>s.</dd><dt><a class="mod" href="event/index.html" title="mod tracing_core::event">event</a></dt><dd>Events represent single points in time during the execution of a program.</dd><dt><a class="mod" href="field/index.html" title="mod tracing_core::field">field</a></dt><dd><code>Span</code> and <code>Event</code> key-value data.</dd><dt><a class="mod" href="metadata/index.html" title="mod tracing_core::metadata">metadata</a></dt><dd>Metadata describing trace data.</dd><dt><a class="mod" href="span/index.html" title="mod tracing_core::span">span</a></dt><dd>Spans represent periods of time in the execution of a program.</dd><dt><a class="mod" href="subscriber/index.html" title="mod tracing_core::subscriber">subscriber</a></dt><dd>Collectors collect and record trace data.</dd></dl><h2 id="macros" class="section-header">Macros<a href="#macros" class="anchor">§</a></h2><dl class="item-table"><dt><a class="macro" href="macro.identify_callsite.html" title="macro tracing_core::identify_callsite">identify_<wbr>callsite</a></dt><dd>Statically constructs an <a href="callsite/struct.Identifier.html" title="struct tracing_core::callsite::Identifier"><code>Identifier</code></a> for the provided <a href="trait.Callsite.html" title="trait tracing_core::Callsite"><code>Callsite</code></a>.</dd><dt><a class="macro" href="macro.metadata.html" title="macro tracing_core::metadata">metadata</a></dt><dd>Statically constructs new span <a href="struct.Metadata.html" title="struct tracing_core::Metadata">metadata</a>.</dd></dl><h2 id="structs" class="section-header">Structs<a href="#structs" class="anchor">§</a></h2><dl class="item-table"><dt><a class="struct" href="struct.Dispatch.html" title="struct tracing_core::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.Event.html" title="struct tracing_core::Event">Event</a></dt><dd><code>Event</code>s represent single points in time where something occurred during the
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execution of a program.</dd><dt><a class="struct" href="struct.Field.html" title="struct tracing_core::Field">Field</a></dt><dd>An opaque key allowing <em>O</em>(1) access to a field in a <code>Span</code>’s key-value
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data.</dd><dt><a class="struct" href="struct.Level.html" title="struct tracing_core::Level">Level</a></dt><dd>Describes the level of verbosity of a span or event.</dd><dt><a class="struct" href="struct.LevelFilter.html" title="struct tracing_core::LevelFilter">Level<wbr>Filter</a></dt><dd>A filter comparable to a verbosity <a href="struct.Level.html" title="struct tracing_core::Level"><code>Level</code></a>.</dd><dt><a class="struct" href="struct.Metadata.html" title="struct tracing_core::Metadata">Metadata</a></dt><dd>Metadata describing a <a href="span/index.html" title="mod tracing_core::span">span</a> or <a href="event/index.html" title="mod tracing_core::event">event</a>.</dd><dt><a class="struct" href="struct.Once.html" title="struct tracing_core::Once">Once</a></dt><dd>A low-level synchronization primitive for one-time global execution.</dd></dl><h2 id="traits" class="section-header">Traits<a href="#traits" class="anchor">§</a></h2><dl class="item-table"><dt><a class="trait" href="trait.Callsite.html" title="trait tracing_core::Callsite">Callsite</a></dt><dd>Trait implemented by callsites.</dd><dt><a class="trait" href="trait.Subscriber.html" title="trait tracing_core::Subscriber">Subscriber</a></dt><dd>Trait representing the functions required to collect trace data.</dd></dl></section></div></main></body></html> |