relay.go
func (r *relayItems) Count() int {
	r.RLock()
	n := len(r.items) - int(r.tombs)
	r.RUnlock()
	return n
}
func (r *relayItems) Count() int {
	r.RLock()
	n := len(r.items) - int(r.tombs)
	r.RUnlock()
	return n
}
// Count returns the number of non-tombstone items in the relay.