public OperationEngineHandler(SessionHandler sessionHandler, int siteId) throws OperationEngineException {
this.sessionHandler = sessionHandler;
//create the op engine.
this.engine = new OperationEngine(siteId);
this.engine.freezeSite(0);
//schedule the purge thread.
this.purgeTimer = new Timer();
this.purgeTask = new PurgeTask();