pub trait RefMetrics: Send + Sync {
// Required methods
fn mailbox_len(&self) -> usize;
fn inflight_count(&self) -> usize;
fn idle_for(&self) -> Duration;
fn silence_for(&self) -> Duration;
fn incarnation(&self) -> u64;
fn is_closed(&self) -> bool;
fn is_terminated(&self) -> bool;
fn stop(&self) -> Result<(), TellError>;
// Provided methods
fn control_mailbox_len(&self) -> usize { ... }
fn pid(&self) -> Pid { ... }
}