code: public static synchronized IDGenerator generatorFor(ZooKeeperConnection zooKeeperConnection,
                                                          String znode,
                                                          Mode mode)
              throws IOException {
  
          if (!instances.containsKey(znode)) {
              final int clusterId = ClusterID.get(zooKeeperConnection.getActiveConnection(), znode);
              SynchronizedGeneratorIdentity generatorIdentityHolder =
                      new SynchronizedGeneratorIdentity(zooKeeperConnection, znode, clusterId, null);
  
              return generatorFor(generatorIdentityHolder, mode);
          }
          return instances.get(znode);
      }
docs: Get the synchronized ID generator instance.
  
  @param zooKeeperConnection Connection to the ZooKeeper quorum.
  @param znode               Base-path of the resource pool in ZooKeeper.
  @param mode                Generator mode.
  @return An instance of this class.
  @throws IOException Thrown when something went wrong trying to find the cluster ID or trying to claim a
  generator ID.