This branch makes the following changes to `tokio-trace`'s `Span` type:
* **Remove manual close API from spans**
In practice, there wasn't really a use-case for this, and it
complicates the implementation a bit. We can always add it back later.
* **Remove generic lifetime from `Span`**
Again, there wasn't actually a use-case for spans with metadata that
doesn't live for the static lifetime, and it made using `Span`s in
other types somewhat inconvenient. It's also possible to implement an
alternative API for non-static spans on top of the `tokio-trace-core`
primitives.
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
* trace-core: Pass dispatcher by ref to `dispatcher::with_default`
As requested by @carllerche in https://github.com/tokio-rs/tokio/pull/966#discussion_r264380005, this branch changes the
`dispatcher::with_default` function in `tokio-trace-core` to take the
dispatcher by ref and perform the clone internally. This makes this
function more consistant with other `with_default` functions in other
crates.
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
* trace: Don't set the default dispatcher on entering a span
Setting the default dispatcher on span entry is a relic of when spans
tracked their parent's ID. At that time, it was necessary to ensure that
any spans created inside a span were observed by the same subscriber
that originally provided the entered span with an ID, as otherwise, new
spans would be created with parent IDs that did not originate from that
subscriber.
Now that spans don't track their parent ID, this is no longer necessary.
However, removing this behavior does mean that if a span is entered
outside of the subscriber context it was created in, any subsequent
spans will be observed by the current default subscriber and thus will
not be part of the original span's trace tree. Since subscribers are not
expected to change frequently, and spans are not expected to move
between them, this is likely acceptable.
I've removed the tests for the old behavior.
Note that this change improves the performance of span entry/exit fairly
significantly. Here are the results of running a benchmark that enters
a span, does nothing, and immediately exits it, before this change:
```
test enter_span ... bench: 93 ns/iter (+/- 14)
```
...and after:
```
test enter_span ... bench: 51 ns/iter (+/- 9)
```
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
This branch changes the `Subscriber::record` method to take a new
arguments struct, `span::Record`. The `field::Record` trait was renamed
to `field::Visit` to prevent name conflicts.
In addition, the `ValueSet::is_empty`, `ValueSet::contains`, and
`ValueSet::record` methods were made crate-private, as they are exposed
on the `Attributes` and `Record` types.
Signed-off-by: Eliza Weisman <elzia@buoyant.io>
This branch allows users of `tokio-trace` to explicitly set a span's
parent, or indicate that a span should be a new root of its own trace
tree. A `parent: ` key has been added to the `span!` macros. When a span
is provided, that span will be set as the parent, while `parent: None`
will result in a new root span. No `parent:` key results in the current
behaviour.
A new type, `span::Attributes`, was added to `tokio-trace-core` to act
as an arguments struct for the `Subscriber::new_span` method. This will
allow future fields to be added without causing breaking API changes.
The `Attributes` struct currently contains the new span's metadata,
`ValueSet`, and parent.
Finally, the `span::Span` type in `-core` was renamed to `span::Id`, for
consistency with `tokio-trace` and to differentiate it from
`span::Attributes`. This name was chosen primarily due to precedent in
other tracing systems.
Closes#920
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
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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 <eliza@buoyant.io>
