code: public void ack(Object msgId) {
  
  		Message msg = this.pendingMessages.remove(msgId);
          JmsMessageID oldest = this.toCommit.first();
          if(msgId.equals(oldest)) {
              if (msg != null) {
                  try {
                      LOG.debug("Committing...");
                      msg.acknowledge();
                      LOG.debug("JMS Message acked: " + msgId);
                      this.toCommit.remove(msgId);
                  } catch (JMSException e) {
                      LOG.warn("Error acknowldging JMS message: " + msgId, e);
                  }
              } else {
                  LOG.warn("Couldn't acknowledge unknown JMS message ID: " + msgId);
              }
          } else {
              this.toCommit.remove(msgId);
          }
  
  	}
docs: /*
  Will only be called if we're transactional or not AUTO_ACKNOWLEDGE