final PhantomReference<Object> frqRef;

  /** Whether or not the background thread started successfully. */
  final boolean threadStarted;

  /** Constructs a new queue. */
  public FinalizableReferenceQueue() {
    // We could start the finalizer lazily, but I'd rather it blow up early.
    queue = new ReferenceQueue<>();
    frqRef = new PhantomReference<>(this, queue);