Why is AbstractClientConnector throwing checkForComodification exception

General
1

What causes a ConcurrentModificationException during the setting of panel contents? What do I have to look for in the component I am adding to avoid this?

Here’s my code:

[code]
private Panel mBodyPanel = new Panel();

private HashMap<String, VerticalLayout> allViews = new HashMap<String, VerticalLayout>();

… create several verticalLayout and store in allViews…

    Button statbtn = new Button(name, new ClickListener()
    {
        @Override
        public void buttonClick(ClickEvent event) {
             VerticalLayout vl = allViews.get("Stats");
             if (vl != null) mBodyPanel.setContent(vl);   <--- Exception thrown here!
        }
    });

[/code]And I am getting this exception:

java.util.ConcurrentModificationException: null
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859) ~[na:1.7.0_51]

    at java.util.ArrayList$Itr.next(ArrayList.java:831) ~[na:1.7.0_51]

    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:589) ~[AbstractClientConnector.class:7.4.6]

    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:621) ~[AbstractComponent.class:7.4.6]

    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) ~[AbstractClientConnector.class:7.4.6]

    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:621) ~[AbstractComponent.class:7.4.6]

    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) ~[AbstractClientConnector.class:7.4.6]

    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:621) ~[AbstractComponent.class:7.4.6]

    at com.vaadin.ui.AbstractComponent.setParent(AbstractComponent.java:528) ~[AbstractComponent.class:7.4.6]

    at com.vaadin.ui.AbstractSingleComponentContainer.setContent(AbstractSingleComponentContainer.java:149) ~[AbstractSingleComponentContainer.class:7.4.6]

    at com.ixiacom.project.gui.component.ports.MultiViewPanel$1.buttonClick(MultiViewPanel.java:70) ~[MultiViewPanel$1.class:na]

    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.7.0_51]

    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[na:1.7.0_51]

    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.7.0_51]

    at java.lang.reflect.Method.invoke(Method.java:606) ~[na:1.7.0_51]

    at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:508) ~[ListenerMethod.class:7.4.6]

    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:198) ~[EventRouter.class:7.4.6]

    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:161) ~[EventRouter.class:7.4.6]

    at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:977) ~[AbstractClientConnector.class:7.4.6]

    at com.vaadin.ui.Button.fireClick(Button.java:393) ~[Button.class:7.4.6]

    at com.vaadin.ui.Button$1.click(Button.java:61) ~[Button$1.class:7.4.6]

    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.7.0_51]

    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[na:1.7.0_51]

    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.7.0_51]

    at java.lang.reflect.Method.invoke(Method.java:606) ~[na:1.7.0_51]

    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:168) ~[ServerRpcManager.class:7.4.6]

    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:118) ~[ServerRpcManager.class:7.4.6]

    at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:291) [ServerRpcHandler.class:7.4.6]

    at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:184) [ServerRpcHandler.class:7.4.6]

    at com.vaadin.server.communication.PushHandler$3.run(PushHandler.java:176) [PushHandler$3.class:7.4.6]

    at com.vaadin.server.communication.PushHandler.callWithUi(PushHandler.java:255) [PushHandler.class:7.4.6]

    at com.vaadin.server.communication.PushHandler.access$200(PushHandler.java:58) [PushHandler.class:7.4.6]

    at com.vaadin.server.communication.PushHandler$1.onRequest(PushHandler.java:78) [PushHandler$1.class:7.4.6]

    at org.atmosphere.cpr.AsynchronousProcessor.action(AsynchronousProcessor.java:205) [AsynchronousProcessor.class:2.2.4.vaadin5]

    at org.atmosphere.cpr.AsynchronousProcessor.suspended(AsynchronousProcessor.java:104) [AsynchronousProcessor.class:2.2.4.vaadin5]

    at org.atmosphere.container.Servlet30CometSupport.service(Servlet30CometSupport.java:66) [Servlet30CometSupport.class:2.2.4.vaadin5]

    at org.atmosphere.cpr.AtmosphereFramework.doCometSupport(AtmosphereFramework.java:2075) [AtmosphereFramework.class:2.2.4.vaadin5]

    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatch(DefaultWebSocketProcessor.java:570) [DefaultWebSocketProcessor.class:2.2.4.vaadin5]

    at org.atmosphere.websocket.DefaultWebSocketProcessor$3.run(DefaultWebSocketProcessor.java:332) [DefaultWebSocketProcessor$3.class:2.2.4.vaadin5]

    at org.atmosphere.util.VoidExecutorService.execute(VoidExecutorService.java:101) [VoidExecutorService.class:2.2.4.vaadin5]

    at org.atmosphere.websocket.DefaultWebSocketProcessor.dispatch(DefaultWebSocketProcessor.java:327) [DefaultWebSocketProcessor.class:2.2.4.vaadin5]

    at org.atmosphere.websocket.DefaultWebSocketProcessor.invokeWebSocketProtocol(DefaultWebSocketProcessor.java:424) [DefaultWebSocketProcessor.class:2.2.4.vaadin5]

    at org.atmosphere.container.JSR356Endpoint$1.onMessage(JSR356Endpoint.java:206) [JSR356Endpoint$1.class:2.2.4.vaadin5]

    at org.atmosphere.container.JSR356Endpoint$1.onMessage(JSR356Endpoint.java:203) [JSR356Endpoint$1.class:2.2.4.vaadin5]

    at org.apache.tomcat.websocket.WsFrameBase.sendMessageText(WsFrameBase.java:375) [tomcat-websocket.jar:8.0.5]

    at org.apache.tomcat.websocket.WsFrameBase.processDataText(WsFrameBase.java:472) [tomcat-websocket.jar:8.0.5]

    at org.apache.tomcat.websocket.WsFrameBase.processData(WsFrameBase.java:275) [tomcat-websocket.jar:8.0.5]

    at org.apache.tomcat.websocket.WsFrameBase.processInputBuffer(WsFrameBase.java:116) [tomcat-websocket.jar:8.0.5]

    at org.apache.tomcat.websocket.server.WsFrameServer.onDataAvailable(WsFrameServer.java:55) [tomcat-websocket.jar:8.0.5]

    at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler$WsReadListener.onDataAvailable(WsHttpUpgradeHandler.java:194) [tomcat-websocket.jar:8.0.5]

    at org.apache.coyote.http11.upgrade.AbstractServletInputStream.onDataAvailable(AbstractServletInputStream.java:194) [tomcat-coyote.jar:8.0.5]

    at org.apache.coyote.http11.upgrade.AbstractProcessor.upgradeDispatch(AbstractProcessor.java:95) [tomcat-coyote.jar:8.0.5]

    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:650) [tomcat-coyote.jar:8.0.5]

    at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222) [tomcat-coyote.jar:8.0.5]

    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1575) [tomcat-coyote.jar:8.0.5]

    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1533) [tomcat-coyote.jar:8.0.5]

    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_51]

    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_51]

    at java.lang.Thread.run(Thread.java:744) [na:1.7.0_51]

I am running Vaadin 7.4.6 with Java 7

Any ideas or pointers on how to track down this issue?

2

Hmmm… Is statbtn inside mBodyPanel’s content? If yes that is the problem.

3

No. The button is in a control section (a CssLayout) that sits on the top of the page that has multiple buttons that control switching the contents of the lower panel. Here’s the hierarchy:

[code]

  • VerticalLayout
    • CssLayout
      • Button ← statBtn
    • Panel ← mBodyLayout
      [/code]Is this potentially a problem?

I am essentially trying to mimick the behavior of a tabbed pane. And this has been working for a while, but only recently it started breaking and I can’t figure out why or how to work around it.

4

Can you attach here the MultiViewPanel codes? Code snippet above can’t show why this is happening.

5

Hi, do you have any overridden attach() methods or added attach listeners that change the component hierarch (add/remove components)? For instance, something like this is not going to work:

class MyLabel extends Label() {
    @Override
    public void attach() {
        super.attach();
        getParent().addComponent(new Button());
    }
}

layout.addComponent(new MyLabel());
panel.setContent(layout);
6

I don’t override any attach() method myself. However, I have a CustomField and I am using the MasonryLayout addon and one of them may be causing this issue.

I traced the problem down to a valueChange that gets fired during a call to addComponent.

In short:
A Custom field’s attach() is calling setInternalValue() which is firing a valueChange event. I have a listener on the field that updates the parent layout when a change happens. I believe the exception occurs in that chain of events.

In detail:
I am using MasonryLayout to display a dashboard of blocks of editable objects in a panel. Each block size and visibility may change due to the user modifying its fields. So all fields are wired to to fire a “dirty” event when any of their values is changed. The listener to the event tells the layout to re-layout the blocks to accomodate for any changes.

This all worked fine until I found that MasonryLayout does not properly detect block size changes and causes blocks to overlap or leave empty gaps. This seems like a bug in MasonryLayout. To get around this issue I found that adding (or removing) an empty (fake) block forces a relayout. This worked well but apparently introduced this error in one of my views (I use this pattern in multiple views).

The error occurs when the first block that contains a CustomField is added. The attach() method is causing setInternalValue() to be invoked and firing a value change event which causes an attempt to add the fake component.