}

  /** Listeners also form a stack through the {@link #listeners} field. */
  private static final class Listener {
    static final Listener TOMBSTONE = new Listener();
    @CheckForNull // null only for TOMBSTONE
    final Runnable task;
    @CheckForNull // null only for TOMBSTONE
    final Executor executor;

    // writes to next are made visible by subsequent CAS's on the listeners field
    @CheckForNull Listener next;

  void setUp() throws Exception {
    if (state != State.NOT_DONE && (numListeners != 0 || numThreads != 0)) {
      throw new SkipThisScenarioException();
    }
  }

  // This exclusion doesn't exclude the TOMBSTONE objects we set. So 'done' NEW futures will look
  // larger than they are.
  @SuppressWarnings("FutureReturnValueIgnored")
  @Footprint(exclude = {Runnable.class, Executor.class, Thread.class, Exception.class})

  void setUp() throws Exception {
    if (state != State.NOT_DONE && (numListeners != 0 || numThreads != 0)) {
      throw new SkipThisScenarioException();
    }
  }

  // This exclusion doesn't exclude the TOMBSTONE objects we set. So 'done' NEW futures will look
  // larger than they are.
  @SuppressWarnings("FutureReturnValueIgnored")
  @Footprint(exclude = {Runnable.class, Executor.class, Thread.class, Exception.class})