code: private byte[] replicas( ) {
      byte[] r = _replicas;
      if( r != null ) return r;
      byte[] nr = new byte[H2O.CLOUD.size()+1/*1-based numbering*/+10/*limit of 10 clients*/];
      if( REPLICAS_UPDATER.compareAndSet(this,null,nr) ) return nr;
      r = _replicas/*read again, since CAS failed must be set now*/;
      assert r!= null;
      return r;
    }
docs: Fills in the _replicas field atomically, on first set of a replica.