2 unstable releases
Uses old Rust 2015
0.1.0 | Apr 22, 2019 |
---|---|
0.0.0 | Nov 27, 2017 |
#814 in Debugging
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tokio-trace
A scoped, structured logging and diagnostics system.
Overview
tokio-trace
is a framework for instrumenting Rust programs to collect
structured, event-based diagnostic information.
In asynchronous systems like Tokio, interpreting traditional log messages can
often be quite challenging. Since individual tasks are multiplexed on the same
thread, associated events and log lines are intermixed making it difficult to
trace the logic flow. tokio-trace
expands upon logging-style diagnostics by
allowing libraries and applications to record structured events with additional
information about temporality and causality — unlike a log message, a span
in tokio-trace
has a beginning and end time, may be entered and exited by the
flow of execution, and may exist within a nested tree of similar spans. In
addition, tokio-trace
spans are structured, with the ability to record typed
data as well as textual messages.
The tokio-trace
crate provides the APIs necessary for instrumenting libraries
and applications to emit trace data.
Usage
First, add this to your Cargo.toml
:
[dependencies]
tokio-trace = "0.1"
Next, add this to your crate:
#[macro_use]
extern crate tokio_trace;
This crate provides macros for creating Span
s and Event
s, which represent
periods of time and momentary events within the execution of a program,
respectively.
As a rule of thumb, spans should be used to represent discrete units of work (e.g., a given request's lifetime in a server) or periods of time spent in a given context (e.g., time spent interacting with an instance of an external system, such as a database). In contrast, events should be used to represent points in time within a span — a request returned with a given status code, n new items were taken from a queue, and so on.
Span
s are constructed using the span!
macro, and then entered
to indicate that some code takes place within the context of that Span
:
// Construct a new span named "my span".
let mut span = span!("my span");
span.enter(|| {
// Any trace events in this closure or code called by it will occur within
// the span.
});
// Dropping the span will close it, indicating that it has ended.
The Event
type represent an event that occurs instantaneously, and is
essentially a Span
that cannot be entered. They are created using the event!
macro:
use tokio_trace::Level;
event!(Level::INFO, "something has happened!");
Users of the log
crate should note that tokio-trace
exposes a set of macros for
creating Event
s (trace!
, debug!
, info!
, warn!
, and error!
) which may
be invoked with the same syntax as the similarly-named macros from the log
crate. Often, the process of converting a project to use tokio-trace
can begin
with a simple drop-in replacement.
Let's consider the log
crate's yak-shaving example:
#[macro_use]
extern crate tokio_trace;
use tokio_trace::field;
pub fn shave_the_yak(yak: &mut Yak) {
// Create a new span for this invocation of `shave_the_yak`, annotated
// with the yak being shaved as a *field* on the span.
span!("shave_the_yak", yak = field::debug(&yak)).enter(|| {
// Since the span is annotated with the yak, it is part of the context
// for everything happening inside the span. Therefore, we don't need
// to add it to the message for this event, as the `log` crate does.
info!(target: "yak_events", "Commencing yak shaving");
loop {
match find_a_razor() {
Ok(razor) => {
// We can add the razor as a field rather than formatting it
// as part of the message, allowing subscribers to consume it
// in a more structured manner:
info!({ razor = field::display(razor) }, "Razor located");
yak.shave(razor);
break;
}
Err(err) => {
// However, we can also create events with formatted messages,
// just as we would for log records.
warn!("Unable to locate a razor: {}, retrying", err);
}
}
}
})
}
You can find examples showing how to use this crate in the examples directory.
In libraries
Libraries should link only to the tokio-trace
crate, and use the provided
macros to record whatever information will be useful to downstream consumers.
In executables
In order to record trace events, executables have to use a Subscriber
implementation compatible with tokio-trace
. A Subscriber
implements a way of
collecting trace data, such as by logging it to standard output.
Unlike the log
crate, tokio-trace
does not use a global Subscriber
which
is initialized once. Instead, it follows the tokio
pattern of executing code
in a context. For example:
#[macro_use]
extern crate tokio_trace;
let my_subscriber = FooSubscriber::new();
tokio_trace::subscriber::with_default(subscriber, || {
// Any trace events generated in this closure or by functions it calls
// will be collected by `my_subscriber`.
})
This approach allows trace data to be collected by multiple subscribers within
different contexts in the program. Alternatively, a single subscriber may be
constructed by the main
function and all subsequent code executed with that
subscriber as the default. Any trace events generated outside the context of a
subscriber will not be collected.
The executable itself may use the tokio-trace
crate to instrument itself as
well.
The tokio-trace-nursery
repository contains less stable crates designed to
be used with the tokio-trace
ecosystem. It includes a collection of
Subscriber
implementations, as well as utility and adapter crates.
License
This project is licensed under the MIT license.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Tokio by you, shall be licensed as MIT, without any additional terms or conditions.