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hawkw subscriber: prepare to release 0.2.1 (#586)
### Changed

- **filter**: `EnvFilter` directive selection now behaves correctly
  (i.e. like `env_logger`) (#583)

### Fixed

- **filter**: Fixed `EnvFilter` incorrectly allowing less-specific
  filter directives to enable events that are disabled by more-specific
  filters (#583)
- **filter**: Multiple significant `EnvFilter`  performance
  improvements, especially when filtering events generated by `log`
  records (#578, #583)
- **filter**: Replaced `BTreeMap` with `Vec` in `DirectiveSet`,
  improving iteration performance significantly with typical numbers of
  filter directives (#580)

A big thank-you to @samschlegel for lots of help with `EnvFilter` 
performance tuning in this release!

Signed-off-by: Eliza Weisman <>
Latest commit 4dad420 Feb 14, 2020
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examples Match changes to std::Backtrace output format (#584) Feb 13, 2020
Cargo.toml subscriber: prepare to release 0.2.1 (#586) Feb 14, 2020 Fix small typos (#405) Oct 24, 2019

Tracing Examples

This directory contains a collection of examples that demonstrate the use of the tracing ecosystem:

  • tracing:
    • counters: Implements a very simple metrics system to demonstrate how subscribers can consume field values as typed data.
    • sloggish: A demo Subscriber implementation that mimics the output of slog-term's Compact formatter.
  • tracing-attributes:
    • attrs-basic: A simple example of the #[instrument] attribute.
    • attrs-args: An example implementing a simple recursive calculation of Fibonacci numbers, to demonstrate how the #[instrument] attribute can record function arguments.
  • tracing-subscriber:
    • fmt: Demonstrates the use of the fmt module in tracing-subscriber, which provides a subscriber implementation that logs traces to the console.
    • fmt-stderr: Demonstrates overriding the output stream used by the fmt subscriber.
    • subscriber-filter: Demonstrates the tracing-subscriber::filter module, which provides a layer which adds configurable filtering to a subscriber implementation.
    • tower-load: Demonstrates how dynamically reloadable filters can be used to debug a server under load in production.
  • tracing-futures:
    • futures-proxy-server: Demonstrates the use of tracing-futures by implementing a simple proxy server, based on this example from tokio.
    • futures-spawn: A simple demonstration of the relationship between the spans representing spawned futures.
  • tracing-tower:
    • tower-h2-client: Demonstrates the use of tracing-tower to instrument a simple tower-h2 HTTP/2 client (based on this example from tower-h2).
    • tower-h2-server: Demonstrates the use of tracing-tower to instrument a simple tower-h2 HTTP/2 server (based on this example from tower-h2).
  • tracing-serde:
    • serde-yak-shave: Demonstrates the use of tracing-serde by implementing a subscriber that emits trace output as JSON.
  • tracing-log:
    • hyper-echo: Demonstrates how tracing-log can be used to record unstructured logs from dependencies as tracing events, by instrumenting this example from hyper, and using tracing-log to record logs emitted by hyper.

The nightly-examples directory contains examples of how tracing can be used with async/await. These are kept separate as async/await is currently only available on nightly Rust toolchains.

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