Filter leak when using WithSubscriber

[jeromegn]

Bug Report

Version

├── tracing v0.1.18 (*)
├── tracing-core v0.1.13 (*)
├── tracing-futures v0.2.4
│   └── tracing v0.1.18 (*)
├── tracing-log v0.1.1
│   └── tracing-core v0.1.13 (*)
├── tracing-subscriber v0.2.10
│   ├── tracing-core v0.1.13 (*)
│   ├── tracing-log v0.1.1 (*)
│   └── tracing-serde v0.1.1
│       └── tracing-core v0.1.13 (*)

Platform

Linux 5.7.12-arch1-1

Crates

tracing-subscriber (probably)

Description

When using the WithSubscriber trait, the filter appears to leak to the global subscriber. At least when not setting any filter.

I'm using a global subscriber with an EnvFilter. If I use something like:

my_future.with_subscriber(tracing_subscriber::Registry::default())

then once my future completes, my global subscriber has "changed" (I think) and no longer filter events or spans according to the original setting. In my use case I was setting the level to "info" and I started getting events and spans with traces up to the "trace" level.

[hawkw]

I think I know what's up here. When a Dispatch is created, we call the callsite::register_dispatch function, which adds the Dispatch to the registry, and registers every callsite with it:

tracing/tracing-core/src/dispatcher.rs

Line 409 in 7f24283

callsite::register_dispatch(&me);

This stores cached filter evaluations from all current subscribers in the per-callsite cache.

However, when a Dispatch is dropped, these cached filters remain in the callsite cache until the next time it is invalidated, either by creating a new Dispatch or by manually calling rebuild_interest_cache. This results in the dropped dispatcher's filters persisting.

I think we ought to change this so that whenever the last clone of a Dispatch is dropped, it re-invalidates the interest cache. I think the easiest way to do this might be changing the Arc<dyn Subscriber + Send + Sync> to a newtype of some kind, and having a Drop impl for that type that calls rebuild_interest_cache.

[hawkw]

@jeromegn the fix I described above should be fairly straightforward to implement, if you're interested in getting another tracing-core commit under your belt. :) Otherwise, I'm happy to do it.

[jeromegn]

I can give it a shot! Will probably ask for help on Discord though :)

[jeromegn]

Confirmed fixed by 2a5da8d