How to check the synchronization is complted or not?

I have written a programme to synchronize the given items as given below. But always getting exception as still the synchronisation is running and can't check the result. Please help me how can I check the synchronisation is completed or not.

final SyncResult syncResult = catalogSynchronizationService.performSynchronization(listOfItems, syncItemJob, syncConfig);
if (syncResult.isFinished()) { result = new ActionResult<>(ActionResult.SUCCESS,null); Messagebox.show(result.getResultCode()); }