## Motivation
Currently, `tokio-trace-core` permits `Subscriber`s to indicate that
they are "always", "sometimes", or "never" interested in a particular
callsite. When "always" or "never" is returned, then the interest is
cached and the subscriber will not be asked again about that callsite.
This is much more efficient than requiring the filter to be re-evaluated
every time the callsite is hit.
However, if a subscriber wishes to change its filter configuration
dynamically at runtime, it cannot benefit from this caching. Instead, it
must always return `Interest::sometimes`. Even when filters change very
infrequently, they must still always be re-evaluated every time.
In order to support a use-case where subscribers may change their filter
configuration at runtime (e.g. tokio-rs/tokio-trace-nursery#42),
but do so infrequently, we should introducing a new function to
invalidate the cached interest.
## Solution
This branch adds a new function in the `callsite` module, called
`rebuild_interest_cache`, that will invalidate and rebuild all cached
interest.
## Breaking Change
In order to fix a race condition that could occur when rebuilding
interest caches using `clear_interest` and `add_interest`, these methods
have been replaced by a new `set_interest` method. `set_interest` should
have the semantics of atomically replacing the previous cached interest,
so that the callsite does not enter a temporary state where it has no
interest.
Closes#1038
Co-Authored-By: yaahallo <[email protected]>
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## Motivation
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. Currently, none
of the available logging frameworks or libraries in Rust offer the
ability to trace logical paths through a futures-based program.
There also are complementary goals that can be accomplished with such a
system. For example, metrics / instrumentation can be tracked by
observing emitted events, or trace data can be exported to a distributed
tracing or event processing system.
In addition, it can often be useful to generate this diagnostic data in
a structured manner that can be consumed programmatically. While prior
art for structured logging in Rust exists, it is not currently
standardized, and is not "Tokio-friendly".
## Solution
This branch adds a new library to the tokio project, `tokio-trace`.
`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-core` crate contains the core primitives for this
system, which are expected to remain stable, while `tokio-trace` crate
provides a more "batteries-included" API. In particular, it provides
macros which are a superset of the `log` crate's `error!`, `warn!`,
`info!`, `debug!`, and `trace!` macros, allowing users to begin the
process of adopting `tokio-trace` by performing a drop-in replacement.
## Notes
Work on this project had previously been carried out in the
[tokio-trace-prototype] repository. In addition to the `tokio-trace` and
`tokio-trace-core` crates, the `tokio-trace-prototype` repo also
contains prototypes or sketches of adapter, compatibility, and utility
crates which provide useful functionality for `tokio-trace`, but these
crates are not yet ready for a release. When this branch is merged, that
repository will be archived, and the remaining unstable crates will be
moved to a new `tokio-trace-nursery` repository. Remaining issues on the
`tokio-trace-prototype` repo will be moved to the appropriate new repo.
The crates added in this branch are not _identical_ to the current head
of the `tokio-trace-prototype` repo, as I did some final clean-up and docs
polish in this branch prior to merging this PR.
[tokio-trace-prototype]: https://github.com/hawkw/tokio-trace-prototypeCloses: #561
Signed-off-by: Eliza Weisman <[email protected]>
Carl Lerche