public void addSessionEventURL(String url,SessionID sid){
  Set<SessionID> sids=sessionEventURLs.get(url);
  if (sids == null) {
    sids=Collections.newSetFromMap(new ConcurrentHashMap<SessionID,Boolean>());
    Set<SessionID> previousValue=sessionEventURLs.putIfAbsent(url,sids);
    if (previousValue != null) {
      sids=previousValue;
    }
  }
  if (sids.add(sid)) {
    notifyPersistenceManager();
  }
}

public void addSessionEventURL ( String url , SessionID sid ) { Set < SessionID > sids = sessionEventURLs . get ( url ) ; if ( sids == null ) { sids = Collections . newSetFromMap ( new ConcurrentHashMap < SessionID , Boolean > ( ) ) ; Set < SessionID > previousValue = sessionEventURLs . putIfAbsent ( url , sids ) ; if ( previousValue != null ) { sids = previousValue ; } } if ( sids . add ( sid ) ) { notifyPersistenceManager ( ) ; } }
adds a listener for the associated session id .
