@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);
    if (!state.permitsPublicUserToTransitionTo(State.FAILURE)) {

            continue restart;
          }
        } else if (!ATOMIC_HELPER.casWaiters(this, curr, succ)) { // We are unlinking head
          continue restart; // We raced with an add or complete
        }
        curr = succ;
      }
      break;
    }
  }

  /** Listeners also form a stack through the {@link #listeners} field. */
  private static final class Listener {

            continue restart;
          }
        } else if (!ATOMIC_HELPER.casWaiters(this, curr, succ)) { // We are unlinking head
          continue restart; // We raced with an add or complete
        }
        curr = succ;
      }
      break;
    }
  }

  /** Listeners also form a stack through the {@link #listeners} field. */
  private static final class Listener {