code: public void noteInternMappingsReceived (Collection<String> sinterns)
      {
          // sanity check
          if (_internmap == null) {
              throw new RuntimeException("Missing intern map");
          }
  
          // make each intern's code positive to signify that we no longer need to send metadata
          for (String sintern : sinterns) {
              Short code = _internmap.get(sintern);
              if (code == null) {
                  throw new RuntimeException("No intern mapping for " + sintern);
              }
              short scode = code;
              if (scode < 0) {
                  _internmap.put(sintern, (short)-code);
              }
          }
      }
docs: Notes that the receiver has received the mappings for a group of interns and thus that from
  now on, only the codes need be sent.