checkNotNull(unit);
    return get();
  }

  @Override
  public void addListener(Runnable runnable, Executor executor) {
    Listener listener = new Listener(runnable, executor);
    if (isDone()) {
      listener.execute();
    } else {
      listeners.add(listener);
    }
  }

  @CanIgnoreReturnValue
  protected boolean setException(Throwable throwable) {
    checkNotNull(throwable);

      return UNSAFE.compareAndSwapObject(future, LISTENERS_OFFSET, expect, update);
    }

    /** Performs a GAS operation on the {@link #listeners} field. */
    @Override
    Listener gasListeners(AbstractFuture<?> future, Listener update) {
      while (true) {
        Listener listener = future.listeners;
        if (update == listener) {