pub fn acquire(issues_dir: &Path, session_id: &str) -> Result<AliveGuard>Expand description
Try to acquire (and hold) an exclusive advisory lock for session_id.
The returned AliveGuard releases the lock when dropped — so callers
must keep it alive for the whole session. Opening with write+create and
calling flock(LOCK_EX | LOCK_NB) is atomic enough for our purposes:
failure to acquire means another live process holds it.