}
public RecordLocation checkpoint() throws JMSException {
RecordLocation rc = super.checkpoint();
final HashMap cpAckedLastAckLocations;
// swap out the hashmaps..
synchronized(this) {
if( rc==null || (this.nextMark!=null && rc.compareTo(this.nextMark)<0) ) {
rc = this.nextMark;
}
cpAckedLastAckLocations = this.ackedLastAckLocations;
this.nextMark=null;
this.ackedLastAckLocations = new HashMap();