Function pair_is_dead 

pub fn pair_is_dead(
    home: &Path,
    id: &str,
    now_ms: i64,
    probe: &dyn ProcessProbe,
) -> bool

The pair’s record is gone, or both its sides read dead or none. The record is looked up by the id in the FILE NAME, and liveness is derived for that id even if the record’s contents disagree. An unreadable record is not “dead”.