Crate tracing_core

source · [−]
Expand description

Core primitives for tracing.

tracing is a framework for instrumenting Rust programs to collect structured, event-based diagnostic information. This crate defines the core primitives of tracing.

This crate provides:

  • span::Id identifies a span within the execution of a program.

  • Event represents a single event within a trace.

  • Subscriber, the trait implemented to collect trace data.

  • Metadata and Callsite provide information describing spans and Events.

  • Field, FieldSet, Value, and ValueSet represent the structured data attached to a span.

  • Dispatch allows spans and events to be dispatched to Subscribers.

In addition, it defines the global callsite registry and per-thread current dispatcher which other components of the tracing system rely on.

Compiler support: requires rustc 1.49+

Usage

Application authors will typically not use this crate directly. Instead, they will use the tracing crate, which provides a much more fully-featured API. However, this crate’s API will change very infrequently, so it may be used when dependencies must be very stable.

Subscriber implementations may depend on tracing-core rather than tracing, as the additional APIs provided by tracing are primarily useful for instrumenting libraries and applications, and are generally not necessary for Subscriber implementations.

The tokio-rs/tracing repository contains less stable crates designed to be used with the tracing ecosystem. It includes a collection of Subscriber implementations, as well as utility and adapter crates.

Crate Feature Flags

The following crate feature flags are available:

  • std: Depend on the Rust standard library (enabled by default).

    no_std users may disable this feature with default-features = false:

    [dependencies]
tracing-core = { version = "0.1.22", default-features = false }

    Note:tracing-core’s no_std support requires liballoc.

Unstable Features

These feature flags enable unstable features. The public API may break in 0.1.x releases. To enable these features, the --cfg tracing_unstable must be passed to rustc when compiling.

The following unstable feature flags are currently available:

Enabling Unstable Features

The easiest way to set the tracing_unstable cfg is to use the RUSTFLAGS env variable when running cargo commands:

RUSTFLAGS="--cfg tracing_unstable" cargo build

Alternatively, the following can be added to the .cargo/config file in a project to automatically enable the cfg flag for that project:

[build]
rustflags = ["--cfg", "tracing_unstable"]

Supported Rust Versions

Tracing is built against the latest stable release. The minimum supported version is 1.49. The current Tracing version is not guaranteed to build on Rust versions earlier than the minimum supported version.

Tracing follows the same compiler support policies as the rest of the Tokio project. The current stable Rust compiler and the three most recent minor versions before it will always be supported. For example, if the current stable compiler version is 1.45, the minimum supported version will not be increased past 1.42, three minor versions prior. Increasing the minimum supported compiler version is not considered a semver breaking change as long as doing so complies with this policy.

Re-exports

pub use self::metadata::Kind;
pub use self::subscriber::Interest;

Modules

callsite
Callsites represent the source locations from which spans or events originate.
dispatcher
Dispatches trace events to Subscribers.
event
Events represent single points in time during the execution of a program.
field
Span and Event key-value data.
metadata
Metadata describing trace data.
span
Spans represent periods of time in the execution of a program.
subscriber
Collectors collect and record trace data.

Macros

identify_callsite
Statically constructs an Identifier for the provided Callsite.
metadata
Statically constructs new span metadata.

Structs

Dispatch
Dispatch trace data to a Subscriber.
Event
Events represent single points in time where something occurred during the execution of a program.
Field
An opaque key allowing O(1) access to a field in a Span’s key-value data.
Level
Describes the level of verbosity of a span or event.
LevelFilter
A filter comparable to a verbosity Level.
Metadata
Metadata describing a span or event.
Once
A synchronization primitive which can be used to run a one-time global initialization. Useful for one-time initialization for FFI or related functionality. This type can only be constructed with Once::new().

Traits

Callsite
Trait implemented by callsites.
Subscriber
Trait representing the functions required to collect trace data.