private void deliver(@Nonnull final List<Deliverable> deliverable)
    {
        pendingElements.addAll(deliverable); // ConcurrentLinkedQueue.addAll is not guaranteed to be atomic. We don't need that, as long as the insertion/iteration order is guaranteed. I'm not sure if it is (but I assume so).
        tryImmediateDelivery();
    }
Delivers the provided data to the client, using the first available
connection, queuing the data of no connection is presently available.

The data is expected to be XMPP-valid.

@param deliverable data to be delivered.
xmppserver/src/main/java/org/jivesoftware/openfire/http/HttpSession.java