code: func NewAtomicWebSocketSet() AtomicWebSocketSet {
  	return AtomicWebSocketSet{
  		sockets: map[uint64]*websocket.Conn{},
  		mutex:   &sync.Mutex{},
  	}
  }
docs: // NewAtomicWebSocketSet returns an AtomicWebSocketSet to maintain open
  // WebSocket connections on a per-user basis.