In Tokio, tasks are optionally instrumented with tracing spans to allow
analysis of the runtime behavior to be performed with tools like
tokio-console.
The span that is created for each task gets currently follows the
default tracing behavior and has a contextual parent attached to it
based on the span that is actual when `tokio::spawn` or similar is
called.
However, in tracing, a span will remain "alive" until all its children
spans are closed. This doesn't match how spawned tasks work. A task may
outlive the context in which is was spawned (and frequently does). This
causes tasks which spawn other - longer living - tasks to appear in
`tokio-console` as having lost their waker when instead they should be
shown as completed (tokio-rs/console#345). It can also cause undesired
behavior for unrelated tracing spans if a subscriber is receiving both
the other spans as well as Tokio's instrumentation.
To fix this mismatch in behavior, the task span has `parent: None` set
on it, making it an explicit root - it has no parent. The same was
already done for all spans representing resources in #6107. This change
is made within the scope of #5792.
Due to a defect in the currently available `tracing-mock` crate, it is
not possible to test this change at a tracing level
(tokio-rs/tracing#2440). Instead, a test for the `console-subscriber`
has been written which shows that this change fixes the defect as
observed in `tokio-console` (tokio-rs/console#490).
A child span stored on sync primitives can keep the parent span open,
unable to be closed by subscribers due to the sync resource referencing it.
Fixes: #6106
Co-authored-by: David Barsky <me@davidbarsky.com>
The documentation for the `Handle::dump()` method includes a description
of the Rust flags needed. However, the sample `.cargo/config.toml` file
is incorrect. It gives the Rust flags as:
```
rustflags = ["--cfg tokio_unstable", "--cfg tokio_taskdump"]
```
However, each command line argument needs to be a separate element in
the array:
```
rustflags = ["--cfg", "tokio_unstable", "--cfg", "tokio_taskdump"]
```
This change corrects that line.
Tokio is instrumented with traces which can be used to analyze the
behavior of the runtime during execution or post-mortem. The
instrumentation is optional. This is where tokio-console collections
information.
There are currently no tests for the instrumentation.
In order to provide more stability to the instrumentation and prepare
for future changes, tests are added to verify the current behavior. The
tests are written using the `tracing-mock` crate. As this crate is still
unreleased, a separate test create has been added under `tokio/tests`
which is outside the workspace. This allows us to pull in both `tracing`
and `tracing-mock` from the tracing repository on GitHub without
affecting the rest of the tokio repository.
This change adds initial tests for the task instrumentation. Further
tests will be added in subsequent commits.
Once `tracing-mock` is published on crates.io (tokio-rs/tracing#539),
these tests can be moved in with the "normal" tokio integration tests.
The decision to add these tests now is due to the release of
`tracing-mock` taking a while, so it would be better to have tests while
we wait.
