Type Alias WatchCallback 

pub type WatchCallback = Arc<dyn Fn(&DnsEvent) + Send + Sync>;

Callback invoked by a backend’s event thread.

Must be Send + Sync because it runs on a native watcher thread. Keep it short: enqueue the event and return. Never call DnsManager::apply, Lease::restore, or other mutating APIs from inside the callback; doing so risks deadlock with the coalescer and reconciler threads.

Aliased Type

pub struct WatchCallback { /* private fields */ }