void clearReferenceQueues() {
      if (map.usesKeyReferences()) {
        clearKeyReferenceQueue();
      }
      if (map.usesValueReferences()) {
        clearValueReferenceQueue();
      }
    }

    void clearKeyReferenceQueue() {
      while (keyReferenceQueue.poll() != null) {}
    }

    void clearValueReferenceQueue() {