@ParametricNullness final K key;
    int index;

    EntryForKey(int index) {
      // The cast is safe because we call forEntry only for indexes that contain entries.
      this.key = uncheckedCastNullableTToT(keys[index]);
      this.index = index;
    }

    void updateIndex() {
      if (index == ABSENT || index > size || !Objects.equal(keys[index], key)) {
        index = findEntryByKey(key);
      }
    }

  int getHash();

  /** Returns the key for this entry. */
  @CheckForNull
  K getKey();

  /*
   * Used by entries that use access order. Access entries are maintained in a doubly-linked list.
   * New entries are added at the tail of the list at write time; stale entries are expired from
   * the head of the list.
   */

  /** Returns the time that this entry was last accessed, in ns. */

    // We need to
    // 1. atomically swap the listeners with TOMBSTONE, this is because addListener uses that
    //    to synchronize with us
    // 2. reverse the linked list, because despite our rather clear contract, people depend on us
    //    executing listeners in the order they were added
    // 3. push all the items onto 'onto' and return the new head of the stack

  int getHash();

  /** Returns the key for this entry. */
  @CheckForNull
  K getKey();

  /*
   * Used by entries that use access order. Access entries are maintained in a doubly-linked list.
   * New entries are added at the tail of the list at write time; stale entries are expired from
   * the head of the list.
   */

  /** Returns the time that this entry was last accessed, in ns. */

    try {
      // if waiting works, this should get stuck
      Queues.drain(q, newArrayList(), 1, MAX_VALUE, NANOSECONDS);
      fail();
    } catch (InterruptedException expected) {
      // we indeed waited; a slow thread had enough time to interrupt us
    }
  }

  // same as above; uninterruptible version
  private void assertUninterruptibleDrained(BlockingQueue<Object> q) {

   * @param newCount the desired count of the element in this multiset
   * @return {@code true} if the condition for modification was met. This implies that the multiset
   *     was indeed modified, unless {@code oldCount == newCount}.
   * @throws IllegalArgumentException if {@code oldCount} or {@code newCount} is negative

   */
  @CheckForNull private transient int[] successor;

  /** Pointer to the first node in the linked list, or {@code ENDPOINT} if there are no entries. */
  private transient int firstEntry;

  /** Pointer to the last node in the linked list, or {@code ENDPOINT} if there are no entries. */
  private transient int lastEntry;

  CompactLinkedHashSet() {
    super();
  }

  private ExecutionSequencer() {}

  /** Creates a new instance. */
  public static ExecutionSequencer create() {
    return new ExecutionSequencer();
  }

  /** This reference acts as a pointer tracking the head of a linked list of ListenableFutures. */
  private final AtomicReference<ListenableFuture<@Nullable Void>> ref =
      new AtomicReference<>(immediateVoidFuture());

   * high 32 bits of each long is the "prev" pointer, whereas the low 32 bits is the "succ" pointer
   * (pointing to the nextEntry entry in the linked list). The pointers in [size(), entries.length)
   * are all "null" (UNSET).
   *
   * <p>A node with "prev" pointer equal to {@code ENDPOINT} is the first node in the linked list,
   * and a node with "nextEntry" pointer equal to {@code ENDPOINT} is the last node.
   */

      // linked list starting from `newTable`. In general, each element from the old linked list
      // belongs to a different linked list from `newTable`. We insert each element in turn at the
      // head of its appropriate `newTable` linked list.
      while (oldNext != UNSET) {
        int entryIndex = oldNext - 1;
        int oldEntry = entries[entryIndex];