@Override
        public boolean available(int port) {
          try {
            ServerSocket sock = new ServerSocket(port);
            sock.close();
            return true;
          } catch (IOException ex) {
            return false;
          }
        }
A set of ports that have been claimed using {@link #randomFreePort()}.
hbase-common/src/test/java/org/apache/hadoop/hbase/HBaseCommonTestingUtil.java