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subscriber: set log max level when reloading (#1270)
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This modifies the `tracing_subscriber::reload` layer to also set the
`log` crate's max level with the current max `tracing` level filter
after reloading. If reloading the subscriber caused the max `tracing`
level to change, this ensures that the change is propagated to the `log`
crate as well. In the case where the max level was made more verbose,
this will ensure that `log` records which were previously disabled are
enabled correctly; in the case where it was made less verbose, this
improve performance by not having to perfrom more costly filtering for
those `log` records.

The `log` max level is set only after rebuilding the callsite interest
cache, which is what sets the max `tracing` level filter. This ensures
that we pass the latest state to the `log` crate.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
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hawkw authored and hds committed Nov 22, 2024
1 parent f6a6c8c commit 6f08af0
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10 changes: 10 additions & 0 deletions tracing-subscriber/src/reload.rs
Original file line number Diff line number Diff line change
Expand Up @@ -317,6 +317,16 @@ impl<L, S> Handle<L, S> {
drop(lock);

callsite::rebuild_interest_cache();

// If the `log` crate compatibility feature is in use, set `log`'s max
// level as well, in case the max `tracing` level changed. We do this
// *after* rebuilding the interest cache, as that's when the `tracing`
// max level filter is re-computed.
#[cfg(feature = "tracing-log")]
tracing_log::log::set_max_level(tracing_log::AsLog::as_log(
&crate::filter::LevelFilter::current(),
));

Ok(())
}

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37 changes: 37 additions & 0 deletions tracing-subscriber/tests/reload_max_log_level.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,37 @@
#![cfg(all(feature = "env-filter", feature = "tracing-log"))]

use tracing::{self, Level};
use tracing_mock::{expect, subscriber};
use tracing_subscriber::{filter::LevelFilter, prelude::*, reload};

#[test]
fn reload_max_log_level() {
let (subscriber, finished) = subscriber::mock()
.event(expect::event().at_level(Level::INFO))
.event(expect::event().at_level(Level::DEBUG))
.event(expect::event().at_level(Level::INFO))
.only()
.run_with_handle();
let (filter, reload_handle) = reload::Layer::new(LevelFilter::INFO);
subscriber.with(filter).init();

assert!(log::log_enabled!(log::Level::Info));
assert!(!log::log_enabled!(log::Level::Debug));
assert!(!log::log_enabled!(log::Level::Trace));

log::debug!("i'm disabled");
log::info!("i'm enabled");

reload_handle
.reload(Level::DEBUG)
.expect("reloading succeeds");

assert!(log::log_enabled!(log::Level::Info));
assert!(log::log_enabled!(log::Level::Debug));
assert!(!log::log_enabled!(log::Level::Trace));

log::debug!("i'm enabled now");
log::info!("i'm still enabled, too");

finished.assert_finished();
}

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