*
 * <p>Rate limiters are often used to restrict the rate at which some physical or logical resource
 * is accessed. This is in contrast to {@link java.util.concurrent.Semaphore} which restricts the
 * number of concurrent accesses instead of the rate (note though that concurrency and rate are
 * closely related, e.g. see <a href="http://en.wikipedia.org/wiki/Little%27s_law">Little's
 * Law</a>).
 *

   * access. Access time is reset by all cache read and write operations (including {@code
   * Cache.asMap().get(Object)} and {@code Cache.asMap().put(K, V)}), but not by {@code
   * containsKey(Object)}, nor by operations on the collection-views of {@link Cache#asMap}}. So,
   * for example, iterating through {@code Cache.asMap().entrySet()} does not reset access time for
   * the entries you retrieve.
   *

 */
@GwtIncompatible // not worth using in GWT for now
@ElementTypesAreNonnullByDefault
class CompactHashSet<E extends @Nullable Object> extends AbstractSet<E> implements Serializable {
  // TODO(user): cache all field accesses in local vars

  /** Creates an empty {@code CompactHashSet} instance. */
  public static <E extends @Nullable Object> CompactHashSet<E> create() {
    return new CompactHashSet<>();
  }

  /**

 *
 * <p>Rate limiters are often used to restrict the rate at which some physical or logical resource
 * is accessed. This is in contrast to {@link java.util.concurrent.Semaphore} which restricts the
 * number of concurrent accesses instead of the rate (note though that concurrency and rate are
 * closely related, e.g. see <a href="http://en.wikipedia.org/wiki/Little%27s_law">Little's
 * Law</a>).
 *

 */
@GwtIncompatible // not worth using in GWT for now
@ElementTypesAreNonnullByDefault
class CompactHashSet<E extends @Nullable Object> extends AbstractSet<E> implements Serializable {
  // TODO(user): cache all field accesses in local vars

  /** Creates an empty {@code CompactHashSet} instance. */
  public static <E extends @Nullable Object> CompactHashSet<E> create() {
    return new CompactHashSet<>();
  }

  /**

   * access. Access time is reset by all cache read and write operations (including {@code
   * Cache.asMap().get(Object)} and {@code Cache.asMap().put(K, V)}), but not by {@code
   * containsKey(Object)}, nor by operations on the collection-views of {@link Cache#asMap}}. So,
   * for example, iterating through {@code Cache.asMap().entrySet()} does not reset access time for
   * the entries you retrieve.
   *

      for (int i = delegateIndex; i < delegates.size(); i++) {
        if (delegates.get(i).setFuture(inputFuture)) {
          recordCompletion();
          // this is technically unnecessary, but should speed up later accesses
          delegateIndex = i + 1;
          return;
        }
      }
      // If all the delegates were complete, no reason for the next listener to have to

     */
    @GuardedBy("this")
    final Queue<ReferenceEntry<K, V>> writeQueue;

    /**
     * A queue of elements currently in the map, ordered by access time. Elements are added to the
     * tail of the queue on access (note that writes count as accesses).
     */
    @GuardedBy("this")
    final Queue<ReferenceEntry<K, V>> accessQueue;

    /** Accumulates cache statistics. */

   * higher than performing just the operation without enforcing the capacity constraint.
   *
   * This implementation uses a per-segment queue to record a memento of the additions, removals,
   * and accesses that were performed on the map. The queue is drained on writes and when it exceeds
   * its capacity threshold.
   *
   * The Least Recently Used page replacement algorithm was chosen due to its simplicity, high hit

      for (int i = delegateIndex; i < delegates.size(); i++) {
        if (delegates.get(i).setFuture(inputFuture)) {
          recordCompletion();
          // this is technically unnecessary, but should speed up later accesses
          delegateIndex = i + 1;
          return;
        }
      }
      // If all the delegates were complete, no reason for the next listener to have to