* href="https://github.com/google/guava/wiki/GraphsExplained#non-recursiveness">recursively</a>.
   * This is because the {@code forTree()}-based implementations don't keep track of visited nodes,
   * and therefore don't need to call `equals()` or `hashCode()` on the node objects; this saves
   * both time and space versus traversing the same graph using {@code forGraph()}.
   *

      ReferenceQueue<Object> queue,
      PhantomReference<Object> frqReference) {
    this.queue = queue;

    this.finalizableReferenceClassReference = new WeakReference<>(finalizableReferenceClass);

    // Keep track of the FRQ that started us so we know when to stop.
    this.frqReference = frqReference;
  }

  /** Loops continuously, pulling references off the queue and cleaning them up. */

  @VisibleForTesting @CheckForNull transient @Nullable Object[] elements;

  /**
   * Keeps track of metadata like the number of hash table bits and modifications of this data
   * structure (to make it possible to throw ConcurrentModificationException in the iterator). Note
   * that we choose not to make this volatile, so we do less of a "best effort" to track such
   * errors, for better performance.
   */
  private transient int metadata;

    /** The key of the configuration. e.g. true */
    String QUERY_TIMEOUT_LOGGING = "query.timeout.logging";

    /** The key of the configuration. e.g. 10000 */
    String QUERY_TRACK_TOTAL_HITS = "query.track.total.hits";

    /** The key of the configuration. e.g. location */
    String QUERY_GEO_FIELDS = "query.geo.fields";

    /** The key of the configuration. e.g. browser_lang */

    String QUERY_HIGHLIGHT_TERMINAL_CHARS = "queryHighlightTerminalChars";

    String QUERY_HIGHLIGHT_BOUNDARY_CHARS = "queryHighlightBoundaryChars";

    String QUERY_TRACK_TOTAL_HITS_VALUE = "queryTrackTotalHitsValue";

    String CORS_ALLOW_ORIGIN = "CorsAllowOrigin";

    String API_DASHBOARD_RESPONSE_HEADER_LIST = "apiDashboardResponseHeaderList";

   *
   * <p>This class is accessible but not supported in GWT as it references {@link
   * PermittedMetaException}.
   */
  protected final class MultiExceptionListIterator implements ListIterator<E> {
    // TODO: track seen elements when order isn't guaranteed
    // TODO: verify contents afterward
    // TODO: something shiny and new instead of Stack
    // TODO: test whether null is supported (create a Feature)
    /**

   *
   * <p>This class is accessible but not supported in GWT as it references {@link
   * PermittedMetaException}.
   */
  protected final class MultiExceptionListIterator implements ListIterator<E> {
    // TODO: track seen elements when order isn't guaranteed
    // TODO: verify contents afterward
    // TODO: something shiny and new instead of Stack
    // TODO: test whether null is supported (create a Feature)
    /**

  }

  /**
   * A {@code LockGraphNode} associated with each lock instance keeps track of the directed edges in
   * the lock acquisition graph.
   */
  private static class LockGraphNode {

    /**
     * The map tracking the locks that are known to be acquired before this lock, each associated
     * with an example stack trace. Locks are weakly keyed to allow proper garbage collection when
     * they are no longer referenced.

  @VisibleForTesting @CheckForNull transient @Nullable Object[] values;

  /**
   * Keeps track of metadata like the number of hash table bits and modifications of this data
   * structure (to make it possible to throw ConcurrentModificationException in the iterator). Note
   * that we choose not to make this volatile, so we do less of a "best effort" to track such
   * errors, for better performance.
   *

  Set<V> createCollection() {
    return Platform.newLinkedHashSetWithExpectedSize(valueSetCapacity);
  }

  /**
   * {@inheritDoc}
   *
   * <p>Creates a decorated insertion-ordered set that also keeps track of the order in which
   * key-value pairs are added to the multimap.
   *
   * @param key key to associate with values in the collection
   * @return a new decorated set containing a collection of values for one key