code: @Override
    public void assignClient(long clientId) {
      LOG.info("Assigning client " + clientId + " ...");
      synchronized (clientModificationsLock) {
        newlyAssignedClients.add(clientId);
      }
    }
docs: Assigns a client to this dispatcher. If a notification fails to be sent
  to a client, then it will be placed in a queue and the assigned
  dispatcher for each client will try to re-send notifications from that
  queue.
  
  @param clientId the id of the assigned client.