log.info("acknowledging: " + messageID);
   protected void acknowledge(long messageID) throws Throwable   {        // acknowledge a delivery         Delivery d;              synchronized (lock)      {         d = (Delivery)deliveries.remove(new Long(messageID));      }            if (d != null)      {         d.acknowledge(null);      }      else      {              throw new IllegalStateException("Cannot find delivery to acknowledge:" + messageID);      }         }