## Motivation
I was just trying to use tokio-trace for a greenfield project, but I was frustrated to discover that I couldn't really use it easily.
I was using the [`runtime`](https://docs.rs/runtime/0.3.0-alpha.4/runtime/) crate, which transparently spawns a thread pool executor for futures. In that thread pool, there's no way to set a tokio-trace subscriber for the duration of each thread, since you don't control the thread initialization. You *might* be able to wrap every future you spawn with a subscriber call, but that's a lot of work.
I was also confused because the documentation said that setting a subscriber in the main thread would use that subscriber for the rest of the program. That isn't the case, though -- the subscriber will be used only on the main thread, and not on worker threads, etc.
## Solution
I added a function `set_global_default`, which works similarly to the `log` crate:
```rust
tokio_trace::subscriber::set_global_default(FooSubscriber::new());
```
The global subscriber (actually a global `Dispatch`) is a `static mut` protected by an atomic; implementation is copied from the `log` crate. It is used as a fallback if a thread has no `Dispatch` currently set. This is extremely simple to use, and doesn't break any existing functionality.
Performance-wise, thread-local `Dispatch` lookup goes from ~4.5ns to ~5ns, according to the benchmarks. So, barely any runtime overhead. (Presumably there's a little compile-time overhead but idk how to measure that.) Since the atomic guard is only ever written once, it will be shared among a CPU's cores and read very cheaply.
I added some docs to partially address #1151. I also switched the tokio-trace benchmarks to criterion because the nightly benchmarks weren't compiling (missing `dyn` flags?)
## Motivation
Currently, the primary way to use a span is to use `.enter` and pass a
closure to be executed under the span. While that is convenient in many
settings, it also comes with two decently inconvenient drawbacks:
- It breaks control flow statements like `return`, `?`, `break`, and
`continue`
- It require re-indenting a potentially large chunk of code if you wish
it to appear under a span
## Solution
This branch changes the `Span::enter` function to return a scope guard
that exits the span when dropped, as in:
```rust
let guard = span.enter();
// code here is within the span
drop(guard);
// code here is no longer within the span
```
The method previously called `enter`, which takes a closure and
executes it in the span's context, is now called `Span::in_scope`, and
was reimplemented on top of the new `enter` method.
This is a breaking change to `tokio-trace` that will be part of the
upcoming 0.2 release.
Closes#1075
Signed-off-by: Eliza Weisman <[email protected]>
This branch adds links to the master RustDoc published by CI to the
`tokio-trace` and `tokio-trace-core` README. In addition, it fixes a
broken links in the RustDoc for `tokio-trace` and updates the
`tokio-trace-core` RustDoc to match the README.
Signed-off-by: Eliza Weisman <[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]>
James Gilles