// so that the cleanup work is visible to listeners.
      // afterDone() should be generally fast and only used for cleanup work... but in theory can
      // also be recursive and create StackOverflowErrors
      future.afterDone();
      // push the current set of listeners onto next
      next = future.clearListeners(next);
      future = null;

      ListenableFuture<V> localDelegate = delegate;
      if (localDelegate != null) {
        return "delegate=[" + localDelegate + "]";
      }
      return null;
    }

    @Override
    protected void afterDone() {
      delegate = null;
    }
  }

  /**
   * Creates a new {@code ListenableFuture} whose value is a list containing the values of all its