code: final void signalActivateSegment() throws SQLException {
  
        /*
           Note that 'offer' does so only if it can be done
           immediately without exceeding the queue capacity.
           The queue capacity is '1', so this means that
           signals may be ignored. Either way, this message
           will never block.
         */
  
        if(segmentSignalQueue != null) {
           segmentSignalQueue.offer(ACTIVATE_SEGMENT_SIGNAL);
        } else if(activeSegments == 0) { //Single segment, no monitor, started with the one segment deactivated...
           synchronized(this) {
              if(activeSegments == 0) { //... and DCL works here because activeSegments is volatile.
                 segments[0].activate();
                 activeSegments = 1;
              }
           }
        }
     }
docs: Signals that a new segment should be activated.