if (isDone()) {
      listener.execute();
    } else {
      listeners.add(listener);
    }
  }

  @CanIgnoreReturnValue
  protected boolean setException(Throwable throwable) {
    checkNotNull(throwable);
    if (!state.permitsPublicUserToTransitionTo(State.FAILURE)) {
      return false;
    }

    forceSetException(throwable);
    return true;
  }

 * to set the result of the computation through the protected methods {@link #set(Object)}, {@link
 * #setFuture(ListenableFuture)} and {@link #setException(Throwable)}. Subclasses may also override
 * {@link #afterDone()}, which will be invoked automatically when the future completes. Subclasses
 * should rarely override other methods.
 *
 * @author Sven Mawson