* </p>
     */
    void dispatchTo(UserInputReceiver userInput);

    /**
     * Discards the current {@link UserInputReceiver} instance used by this service.
     */
    void stopDispatching();

        if (!delegate.compareAndSet(null, userInput)) {
            throw new IllegalStateException("User input has already been initialized.");
        }
    }

    @Override
    public void stopDispatching() {
        delegate.set(null);
    }

        });
        forwarder = new ForwardingUserInput(inputStream, dispatch, executor);
        userInput.dispatchTo(forwarder);
    }

    @Override
    public void stop() {
        userInput.stopDispatching();
        forwarder.stop();
        executor.shutdown();
    }

    private static class ForwardingUserInput implements UserInputReceiver {
        private final Dispatch<? super InputMessage> dispatch;