Website | Chat | Documentation (master branch)
The master branch is the pre-release, development version of tracing
. Please see the v0.1.x branch for the versions of tracing
released to crates.io.
tracing
is a framework for instrumenting Rust programs to collect
structured, event-based diagnostic information. tracing
is maintained by the
Tokio project, but does not require the tokio
runtime to be used.
In order to record trace events, executables have to use a collector
implementation compatible with tracing
. A collector implements a way of
collecting trace data, such as by logging it to standard output.
tracing-subscriber
's fmt
module provides
a collector for logging traces with reasonable defaults. Additionally,
tracing-subscriber
is able to consume messages emitted by log
-instrumented
libraries and modules.
To use tracing-subscriber
, add the following to your Cargo.toml
:
[dependencies]
tracing = "0.1"
tracing-subscriber = "0.2"
Then create and install a collector, for example using init()
:
use tracing::info;
use tracing_subscriber;
fn main() {
// install global collector configured based on RUST_LOG env var.
tracing_subscriber::fmt::init();
let number_of_yaks = 3;
// this creates a new event, outside of any spans.
info!(number_of_yaks, "preparing to shave yaks");
let number_shaved = yak_shave::shave_all(number_of_yaks);
info!(
all_yaks_shaved = number_shaved == number_of_yaks,
"yak shaving completed."
);
}
Using init()
calls set_global_default()
so this collector will be used
as the default in all threads for the remainder of the duration of the
program, similar to how loggers work in the log
crate.
For more control, a collector can be built in stages and not set globally, but instead used to locally override the default collector. For example:
use tracing::{info, Level};
use tracing_subscriber;
fn main() {
let collector = tracing_subscriber::fmt()
// filter spans/events with level TRACE or higher.
.with_max_level(Level::TRACE)
// build but do not install the subscriber.
.finish();
tracing::collect::with_default(collector, || {
info!("This will be logged to stdout");
});
info!("This will _not_ be logged to stdout");
}
Any trace events generated outside the context of a collector will not be collected.
This approach allows trace data to be collected by multiple collectors within different contexts in the program. Note that the override only applies to the currently executing thread; other threads will not see the change from with_default.
Once a collector has been set, instrumentation points may be added to the
executable using the tracing
crate's macros.
Libraries should only rely on the tracing
crate and use the provided macros
and types to collect whatever information might be useful to downstream consumers.
use std::{error::Error, io};
use tracing::{debug, error, info, span, warn, Level};
// the `#[tracing::instrument]` attribute creates and enters a span
// every time the instrumented function is called. The span is named after
// the function or method. Parameters passed to the function are recorded as fields.
#[tracing::instrument]
pub fn shave(yak: usize) -> Result<(), Box<dyn Error + 'static>> {
// this creates an event at the DEBUG level with two fields:
// - `excitement`, with the key "excitement" and the value "yay!"
// - `message`, with the key "message" and the value "hello! I'm gonna shave a yak."
//
// unlike other fields, `message`'s shorthand initialization is just the string itself.
debug!(excitement = "yay!", "hello! I'm gonna shave a yak.");
if yak == 3 {
warn!("could not locate yak!");
// note that this is intended to demonstrate `tracing`'s features, not idiomatic
// error handling! in a library or application, you should consider returning
// a dedicated `YakError`. libraries like snafu or thiserror make this easy.
return Err(io::Error::new(io::ErrorKind::Other, "shaving yak failed!").into());
} else {
debug!("yak shaved successfully");
}
Ok(())
}
pub fn shave_all(yaks: usize) -> usize {
// Constructs a new span named "shaving_yaks" at the TRACE level,
// and a field whose key is "yaks". This is equivalent to writing:
//
// let span = span!(Level::TRACE, "shaving_yaks", yaks = yaks);
//
// local variables (`yaks`) can be used as field values
// without an assignment, similar to struct initializers.
let span = span!(Level::TRACE, "shaving_yaks", yaks);
let _enter = span.enter();
info!("shaving yaks");
let mut yaks_shaved = 0;
for yak in 1..=yaks {
let res = shave(yak);
debug!(yak, shaved = res.is_ok());
if let Err(ref error) = res {
// Like spans, events can also use the field initialization shorthand.
// In this instance, `yak` is the field being initialized.
error!(yak, error = error.as_ref(), "failed to shave yak!");
} else {
yaks_shaved += 1;
}
debug!(yaks_shaved);
}
yaks_shaved
}
[dependencies]
tracing = "0.1"
Note: Libraries should NOT install a collector by using a method that calls
set_global_default()
, as this will cause conflicts when executables try to
set the default later.
To trace async fn
s, the preferred method is using the #[instrument]
attribute:
use tracing::{info, instrument};
use tokio::{io::AsyncWriteExt, net::TcpStream};
use std::io;
#[instrument]
async fn write(stream: &mut TcpStream) -> io::Result<usize> {
let result = stream.write(b"hello world\n").await;
info!("wrote to stream; success={:?}", result.is_ok());
result
}
Special handling is needed for the general case of code using
std::future::Future
or blocks with async
/await
, as the
following example will not work:
async {
let _s = span.enter();
// ...
}
The span guard _s
will not exit until the future generated by the async
block is complete.
Since futures and spans can be entered and exited multiple times without them completing,
the span remains entered for as long as the future exists, rather than being entered only when
it is polled, leading to very confusing and incorrect output.
For more details, see the documentation on closing spans.
This problem can be solved using the Future::instrument
combinator:
use tracing::Instrument;
let my_future = async {
// ...
};
my_future
.instrument(tracing::info_span!("my_future"))
.await
Future::instrument
attaches a span to the future, ensuring that the span's lifetime
is as long as the future's.
Under the hood, the #[instrument]
macro performs same the explicit span
attachment that Future::instrument
does.
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.
First, see if the answer to your question can be found in the API documentation. If the answer is not there, there is an active community in the Tracing Discord channel. We would be happy to try to answer your question. Last, if that doesn't work, try opening an issue with the question.
๐ Thanks for your help improving the project! We are so happy to have you! We have a contributing guide to help you get involved in the Tracing project.
The tracing
crate contains the primary instrumentation API, used for
instrumenting libraries and applications to emit trace data. The tracing-core
crate contains the core API primitives on which the rest of tracing
is
instrumented. Authors of trace subscribers may depend on tracing-core
, which
guarantees a higher level of stability.
Additionally, this repository contains several compatibility and utility
libraries built on top of tracing
. Some of these crates are in a pre-release
state, and are less stable than the tracing
and tracing-core
crates.
The crates included as part of Tracing are:
-
tracing-futures
: Utilities for instrumentingfutures
. (crates.io|docs) -
tracing-macros
: Experimental macros for emitting trace events (unstable). -
tracing-attributes
: Procedural macro attributes for automatically instrumenting functions. (crates.io|docs) -
tracing-log
: Compatibility with thelog
crate (unstable). -
tracing-opentelemetry
: Provides a layer that connects spans from multiple systems into a trace and emits them to OpenTelemetry-compatible distributed tracing systems for processing and visualization. (crates.io|docs) -
tracing-serde
: A compatibility layer for serializing trace data withserde
(unstable). -
tracing-subscriber
: Collector implementations, and utilities for implementing and composingCollector
s. (crates.io|docs) -
tracing-tower
: Compatibility with thetower
ecosystem (unstable). -
tracing-appender
: Utilities for outputting tracing data, including a file appender and non-blocking writer. (crates.io|docs) -
tracing-error
: ProvidesSpanTrace
, a type for instrumenting errors with tracing spans -
tracing-flame
; Provides a layer for generating flame graphs based on tracing span entry / exit events. -
tracing-journald
: Provides a layer for recording events to the Linuxjournald
service, preserving structured data.
In addition to this repository, here are also several third-party crates which
are not maintained by the tokio
project. These include:
tracing-timing
implements inter-event timing metrics on top oftracing
. It provides a subscriber that records the time elapsed between pairs oftracing
events and generates histograms.tracing-honeycomb
Provides a layer that reports traces spanning multiple machines to honeycomb.io. Backed bytracing-distributed
.tracing-distributed
Provides a generic implementation of a layer that reports traces spanning multiple machines to some backend.tracing-actix-web
providestracing
integration for theactix-web
web framework.tracing-actix
providestracing
integration for theactix
actor framework.tracing-gelf
implements a subscriber for exporting traces in Greylog GELF format.tracing-coz
provides integration with the coz causal profiler (Linux-only).tracing-bunyan-formatter
provides a layer implementation that reports events and spans in bunyan format, enriched with timing information.tide-tracing
provides a tide middleware to trace all incoming requests and responses.color-spantrace
provides a formatter for rendering span traces in the style ofcolor-backtrace
color-eyre
provides customized panic and eyre report handlers foreyre::Report
for capturing span traces and backtraces with new errors and pretty printing them.spandoc
provides a proc macro for constructing spans from doc comments inside of functions.tracing-wasm
provides aCollector
/Subscriber
implementation that reports events and spans via browserconsole.log
and User Timing API (window.performance
).test-log
takes care of initializingtracing
for tests, based on environment variables with anenv_logger
compatible syntax.tracing-unwrap
provides convenience methods to report failed unwraps onResult
orOption
types to aCollector
.diesel-tracing
provides integration withdiesel
database connections.tracing-tracy
provides a way to collect Tracy profiles in instrumented applications.tracing-elastic-apm
provides a layer for reporting traces to Elastic APM.tracing-etw
provides a layer for emitting Windows ETW events.sentry-tracing
provides a layer for reporting events and traces to Sentry.tracing-forest
provides a subscriber that preserves contextual coherence by grouping together logs from the same spans during writing.tracing-loki
provides a layer for shipping logs to Grafana Loki.
(if you're the maintainer of a tracing
ecosystem crate not in this list,
please let us know!)
Note: that some of the ecosystem crates are currently unreleased and
undergoing active development. They may be less stable than tracing
and
tracing-core
.
This is a list of links to blog posts, conference talks, and tutorials about Tracing.
- Diagnostics with Tracing on the Tokio blog, August 2019
- Production-Grade Logging in Rust Applications, November 2020
- Custom Logging in Rust using
tracing
andtracing-subscriber
, part 1 and part 2, October 2021
- Bay Area Rust Meetup talk and Q&A, March 2019
- RustConf 2019 talk and slides, August 2019
- Are we observable yet? @ RustyDays talk and slides, August 2020
Help us expand this list! If you've written or spoken about Tracing, or know of resources that aren't listed, please open a pull request adding them.
This project is licensed under the MIT license.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Tracing by you, shall be licensed as MIT, without any additional terms or conditions.