Function register_invalidator_on 

pub fn register_invalidator_on<E, F>(
    dispatcher: &EventDispatcher,
    cache: Arc<Cache>,
    key_fn: F,
)
where
    E: Event,
    F: Fn(&E) -> Vec<String> + Send + Sync + 'static,

Register a cache-invalidation listener on an arbitrary EventDispatcher.

When an event of type E is dispatched through dispatcher, key_fn is invoked with the event to compute the set of tags to flush. Each tag is flushed via Cache::tags + crate::TaggedCache::flush; per-tag flush failures are tracing::warn!’d and swallowed at the dispatcher boundary so a degraded cache cannot brick the write path that fired the event.

Multiple invalidators may be registered for the same event type on the same dispatcher — all run; order between them is unspecified.

Prefer register_invalidator for the common case of registering on the process-wide global_dispatcher. Use this overload when the consumer holds a non-global dispatcher (isolated per-tenant context, per-test fixture, embedded library inside a larger app, …).

Parameters

• dispatcher: the dispatcher to register the listener on.
• cache: an Arc<Cache> whose store backs the tag flushing.
• key_fn: a closure Fn(&E) -> Vec<String> returning the tags to flush. Returning an empty Vec is a no-op (and skips the per-tag flush calls).