* call cancel() and be unable to cancel the delegate.
   * There are a number of ways to solve this, none of which are very pretty, and it is currently
   * believed to be a purely theoretical problem (since the other actions should supply sufficient
   * write-barriers).
   */

  @LazyInit private @Nullable ListenableFuture<V> delegateRef;
  @LazyInit private @Nullable ScheduledFuture<?> timer;