Steps to Reproduce

1. run with Firefox
2. click Start button
3. wait for more than 1 minute

Current Result

18:03:25.338 [http-nio-8080-exec-6] WARN o.z.z.au.websocket.WebSocketEndPoint - SERVER ERROR
org.zkoss.zk.ui.UiException: java.lang.IllegalMonitorStateException
at org.zkoss.zkmax.au.websocket.WebSocketEndPoint$1.onMessage(WebSocketEndPoint.java:176)
at org.zkoss.zkmax.au.websocket.WebSocketEndPoint$1.onMessage(WebSocketEndPoint.java:153)
at org.apache.tomcat.websocket.WsFrameBase.sendMessageText(WsFrameBase.java:401)
at org.apache.tomcat.websocket.server.WsFrameServer.sendMessageText(WsFrameServer.java:119)
at org.apache.tomcat.websocket.WsFrameBase.processDataText(WsFrameBase.java:502)
at org.apache.tomcat.websocket.WsFrameBase.processData(WsFrameBase.java:301)
at org.apache.tomcat.websocket.WsFrameBase.processInputBuffer(WsFrameBase.java:133)
at org.apache.tomcat.websocket.server.WsFrameServer.onDataAvailable(WsFrameServer.java:82)
at org.apache.tomcat.websocket.server.WsFrameServer.doOnDataAvailable(WsFrameServer.java:171)
at org.apache.tomcat.websocket.server.WsFrameServer.notifyDataAvailable(WsFrameServer.java:151)
at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.upgradeDispatch(WsHttpUpgradeHandler.java:148)
at org.apache.coyote.http11.upgrade.UpgradeProcessorInternal.dispatch(UpgradeProcessorInternal.java:54)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:59)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:818)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1626)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: java.lang.IllegalMonitorStateException: null
at java.base/java.lang.Object.notify(Native Method)
at org.zkoss.zkmax.au.websocket.WebSocketServerPush.setReady(WebSocketServerPush.java:76)
at org.zkoss.zkmax.au.websocket.WebSocketEndPoint.process(WebSocketEndPoint.java:288)
at org.zkoss.zkmax.au.websocket.WebSocketEndPoint$1.onMessage(WebSocketEndPoint.java:172)
... 19 common frames omitted

Expected Result

no such error

Debug Information

• this bug affects demo
• someone can reproduce it with chrome, Windows