}
private static final EventQueueProvider getProvider() {
if (_provider == null)
synchronized (EventQueues.class) {
if (_provider == null) {
EventQueueProvider provider = null;
String clsnm = Library.getProperty("org.zkoss.zk.ui.event.EventQueueProvider.class");
if (clsnm == null)
clsnm = Library.getProperty("org.zkoss.zkmax.ui.EventQueueProvider.class");
//backward compatible
if (clsnm != null)