* Commences a shutdown of this dispatch.
     */
    @Override
    public void requestStop() {
        lock.lock();
        try {
            doRequestStop();
        } finally {
            lock.unlock();
        }
    }

    private void doRequestStop() {
        setState(State.Stopped);
    }

    /**
     * Stops accepting new messages, and blocks until all queued messages have been dispatched.