code: func (m *Manager) closeWatchLocked(proxyID string, watchIdx uint64) {
  	if watchers, ok := m.watchers[proxyID]; ok {
  		if ch, ok := watchers[watchIdx]; ok {
  			delete(watchers, watchIdx)
  			close(ch)
  			if len(watchers) == 0 {
  				delete(m.watchers, proxyID)
  			}
  		}
  	}
  }
docs: // closeWatchLocked cleans up state related to a single watcher. It assumes the
  // lock is held.