Module observer 

Three-tier observer resolution + the Observer trait.

Spec 11 § 3:

• Per-task OBSERVER_TASK (highest priority; via Future::with_observer adapter, lands in spec 13 § 3 / Phase 3 task 3.3).
• Per-thread OBSERVER_THREAD — with_observer_thread_local, with_test_observer, #[obs::test].
• Global OBSERVER_GLOBAL — install_observer.

The hot path checks OVERRIDE_COUNT == 0 first so a process that never installs an override pays one atomic load and one ArcSwap::load_full. The CAN_ENTER cell prevents re-entry when a sink synthesises an event.

Structs

InMemoryHandle

Stable handle to an InMemorySink. Clone-safe; share across threads.

InMemoryObserver

Test-grade observer: every envelope is delivered to an InMemorySink. Spec 61 § 2.4 example.

NoopObserver

The default observer: drops every envelope.

StandardObserver

Production-ready observer with reloadable config and per-tier worker pool.

StandardObserverBuilder

Builder for StandardObserver.

ThreadObserverGuard

RAII guard returned by with_observer_thread_local.

WeakObserver

Weak handle for code that needs to refer to the observer without extending its lifetime — chiefly sinks that internally hold callbacks back into the observer (e.g. the future ObsToTracingSink re-emitting through the registered tracing dispatcher).

WorkerCounters

Per-tier counters surfaced as ObsSinkDropped self-events.

Enums

BuildError

Errors returned by StandardObserverBuilder::build.

Traits

Observer

The global observer trait. Sealed in spirit (downstream crates implement it freely, but the SDK ships NoopObserver, InMemoryObserver, StandardObserver covering 99% of cases).

Functions

enter_emit_envelope

Dispatch one envelope through the observer with the re-entry guard held. Spec 11 § 3.1 “Re-entry and the CAN_ENTER cell”.

install_observer

Install the global observer. Called once at process start.

install_observer_arc

Install a pre-arc’d observer. Convenience for tests and patterns that already have an Arc<dyn Observer> (e.g. multi-tenant registries).

observer

Resolve the active observer.

observer_weak

Weak handle to whatever observer() would return right now.

with_observer_task

Async sibling of with_test_observer: install the observer in the per-task slot for the duration of fut. This is the version the #[obs::test] async expansion uses so that an emit on a migrated-tokio-worker-thread still resolves to the test observer (the per-thread slot would not be set on the destination worker).

with_observer_task_sync

Synchronous sibling of with_observer_task used by Instrumented<F>::poll so a single poll can bind / unbind the per-task observer without requiring an await. Spec 13 § 3.

with_observer_thread_local

Sync RAII guard. Sets the per-thread observer override; restores the previous value on drop. Do not hold across .await — see the warning in spec 11 § 3.1; use Future::with_observer (Phase 3 task 3.3) for async.

with_test_observer

Test-flavored helper. Installs the observer per-thread for the duration of f; restores on closure exit. Used by #[obs::test] (Phase 2 task 2.6) and by users that want to assert what was emitted from a synchronous block.