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executor: switch from log to tracing (#1454)

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## Motivation

The `tracing` crate implements scoped, structured, context-aware
diagnostics, which can add significant debugging value over unstructured
log messages. `tracing` is part of the Tokio project. As part of the
`tokio` 0.2 changes, I thought it would be good to move over from `log`
to `tracing` in the tokio runtime. Updating the executor crate is an obvious
starting point. 

## Solution

This branch replaces the use of `log` in `tokio-executor` with
`tracing`. I've tried to leave all the instrumentation points more or
less the same, but modified to use structured fields instead of string
interpolation. I've also added a few `tracing` spans, primarily in
places where a variable is added to all the log messages in a scope.

## Notes

For users who are using the legacy `log` output, there is a feature flag
to enable `log` support in `tracing`. I thought about making this on by
default, but that would also enable the `tracing` dependency by default,
and it is only pulled in when the `threadpool` feature flag is enabled.
The `tokio` crate could enable the log feature in its default features
instead, since the threadpool feature is on by default in `tokio`. If
this isn't the right approach, I can change how `log` back-compatibility
is enabled.

We might want to consider adding more `tracing` spans in the threadpool
later. This could be useful for profiling, and for helping users debug
the way their applications interact with the executor. This branch is
just intended as a starting point so that we can begin emitting
`tracing` data from the executor; we should revisit what instrumentation
should be exposed, as well.

Signed-off-by: Eliza Weisman <[email protected]>
This commit is contained in:
Eliza Weisman
2019-08-20 12:44:26 -07:00
committed by GitHub
parent 2d56312b89
commit 7e7a5147a3
10 changed files with 138 additions and 42 deletions
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tokio-executor/Cargo.toml
+2 -2
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@@ -30,7 +30,6 @@ threadpool = [
"futures-core-preview",
"futures-util-preview",
"num_cpus",
"log",
"lazy_static",
"slab",
]
@@ -38,6 +37,8 @@ threadpool = [
[dependencies]
tokio-sync = { version = "=0.2.0-alpha.2", optional = true, path = "../tokio-sync" }
tracing = { version = "0.1.5", optional = true }
# current-thread dependencies
crossbeam-channel = { version = "0.3.8", optional = true }
@@ -48,7 +49,6 @@ crossbeam-utils = { version = "0.6.4", optional = true }
futures-core-preview = { version = "=0.3.0-alpha.18", optional = true }
futures-util-preview = { version = "=0.3.0-alpha.18", optional = true }
num_cpus = { version = "1.2", optional = true }
log = { version = "0.4", optional = true }
lazy_static = { version = "1", optional = true }
slab = { version = "0.4.1", optional = true }