code: int getAveMapSlotRefillMsecs() {
      synchronized (mapSlotRefillMsecsQueue) {
        if (mapSlotRefillMsecsQueue.isEmpty()) {
          return -1;
        }
  
        int totalMapSlotRefillMsecs = 0;
        for (int refillMsecs : mapSlotRefillMsecsQueue) {
          totalMapSlotRefillMsecs += refillMsecs;
        }
        return totalMapSlotRefillMsecs / mapSlotRefillMsecsQueue.size();
      }
    }
docs: Get the average time in milliseconds to refill a free map slot.  This
  average is calculated on a rotating buffer.
  
  @return Average time in milliseconds to refill a free map slot.  Return -1
  if the value is not valid (hasn't actually refilled anything)