tx.addCallback(callback);
this.getCallback(tx).addDelivery(d);
   public void acknowledge(Delivery d, Transaction tx) throws Throwable   {      //Transactional so remove after tx commit      RemoveDeliveryCallback callback = new RemoveDeliveryCallback(d);            tx.addCallback(callback);            if (trace) { log.trace(this + " added " + d + " to memory on transaction " + tx); }            if (recoverable && d.getReference().isReliable())      {                  pm.removeReference(channel.getChannelID(), d.getReference(), tx);                 }                }