ConcurrentModificationException While not under load

[nathandennis]

Having trouble with an exception just after ajax call.
jboss 4.2.2
seam 2.0.1.ga
richfaces 3.2

the expection

19:04:00,004 ERROR [SeamPhaseListener] uncaught exception
java.util.ConcurrentModificationException
        at java.util.SubList.checkForComodification(AbstractList.java:855)
        at java.util.SubList.size(AbstractList.java:728)
        at org.jboss.seam.contexts.EntityBeanList.passivateAll(EntityBeanList.java:68)
        at org.jboss.seam.contexts.AbstractEntityBeanCollection.passivate(AbstractEntityBeanCollection.java:43)
        at org.jboss.seam.contexts.ServerConversationContext.isAttributeDirty(ServerConversationContext.java:307)
        at org.jboss.seam.contexts.ServerConversationContext.flush(ServerConversationContext.java:280)
        at org.jboss.seam.contexts.Contexts.flushAndDestroyContexts(Contexts.java:371)
        at org.jboss.seam.contexts.FacesLifecycle.endRequest(FacesLifecycle.java:112)
        at org.jboss.seam.jsf.SeamPhaseListener.afterRenderResponse(SeamPhaseListener.java:502)
        at org.jboss.seam.jsf.SeamPhaseListener.afterServletPhase(SeamPhaseListener.java:235)
        at org.jboss.seam.jsf.SeamPhaseListener.afterPhase(SeamPhaseListener.java:182)
        at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:280)
        at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:144)
        at javax.faces.webapp.FacesServlet.service(FacesServlet.java:245)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:83)
        at org.jboss.seam.debug.hot.HotDeployFilter.doFilter(HotDeployFilter.java:68)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
        at org.jboss.seam.web.ExceptionFilter.doFilter(ExceptionFilter.java:64)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
        at org.jboss.seam.web.RedirectFilter.doFilter(RedirectFilter.java:45)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
        at org.ajax4jsf.webapp.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:147)
        at org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:276)
        at org.ajax4jsf.Filter.doFilter(Filter.java:175)
        at org.jboss.seam.web.Ajax4jsfFilter.doFilter(Ajax4jsfFilter.java:60)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
        at org.jboss.seam.web.LoggingFilter.doFilter(LoggingFilter.java:58)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
        at org.jboss.seam.servlet.SeamFilter.doFilter(SeamFilter.java:158)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
        at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:179)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:432)
        at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
        at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
        at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446)
        at java.lang.Thread.run(Thread.java:595)
19:04:00,006 ERROR [SeamPhaseListener] swallowing exception
java.util.ConcurrentModificationException
        at java.util.SubList.checkForComodification(AbstractList.java:855)
        at java.util.SubList.size(AbstractList.java:728)
        at org.jboss.seam.contexts.EntityBeanList.passivateAll(EntityBeanList.java:68)
        at org.jboss.seam.contexts.AbstractEntityBeanCollection.passivate(AbstractEntityBeanCollection.java:43)
        at org.jboss.seam.contexts.ServerConversationContext.isAttributeDirty(ServerConversationContext.java:307)
        at org.jboss.seam.contexts.ServerConversationContext.flush(ServerConversationContext.java:280)
        at org.jboss.seam.contexts.Contexts.flushAndDestroyContexts(Contexts.java:371)
        at org.jboss.seam.contexts.FacesLifecycle.endRequest(FacesLifecycle.java:112)
        at org.jboss.seam.jsf.SeamPhaseListener.afterRenderResponse(SeamPhaseListener.java:502)
        at org.jboss.seam.jsf.SeamPhaseListener.afterServletPhase(SeamPhaseListener.java:235)
        at org.jboss.seam.jsf.SeamPhaseListener.afterPhase(SeamPhaseListener.java:182)
        at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:280)
        at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:144)
        at javax.faces.webapp.FacesServlet.service(FacesServlet.java:245)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:83)
        at org.jboss.seam.debug.hot.HotDeployFilter.doFilter(HotDeployFilter.java:68)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
        at org.jboss.seam.web.ExceptionFilter.doFilter(ExceptionFilter.java:64)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
        at org.jboss.seam.web.RedirectFilter.doFilter(RedirectFilter.java:45)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
        at org.ajax4jsf.webapp.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:147)
        at org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:276)
        at org.ajax4jsf.Filter.doFilter(Filter.java:175)
        at org.jboss.seam.web.Ajax4jsfFilter.doFilter(Ajax4jsfFilter.java:60)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
        at org.jboss.seam.web.LoggingFilter.doFilter(LoggingFilter.java:58)
        at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
        at org.jboss.seam.servlet.SeamFilter.doFilter(SeamFilter.java:158)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
        at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:179)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:432)
        at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
        at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
        at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446)
        at java.lang.Thread.run(Thread.java:595)

there are a bunch of ajax request on this page.. and this two are the only ones giving trouble.

now some code.

@Stateful
@Name("picAction")
@Scope(ScopeType.CONVERSATION)
public class PicAction implements PicLocal, DropListener, Serializable 

....

     public void switchLayer(boolean layer, int layerindex){
          if (layer == false && this.layerselectlock==false && this.activelayer >= 0){
               saveOrder();
               if(activelayer < layerframe2.size() -1 ){
                         subreindex = layerframe2.subList(activelayer + 1, layerframe2.size());
                    
                    long startingpoint = subreindex.get(0).getPoz();
                    log.info("after sublist");
                    for(int i = 0; i < subreindex.size(); i++ ){     
                                     subreindex.get(i).setPoz(startingpoint - (long)1 + (long)i );
                              entityManager.merge(subreindex.get(i));                    
               }
                                   if(layerframe2.get(activelayer).getMark() == 107){
                         FileDeleteLocal removelayer = (FileDeleteLocal) Component.getInstance("fileDeleteAction");
                         removelayer.deleteMedia(layerframe2.get(activelayer).getLayername(),
                                        layerframe2.get(activelayer).getUserid());
                    }else {               entityManager.remove(entityManage               .find(Layers.class, layerframe2.get(activelayer).getId()));
                    }
               layerselectlock = true;
               initEdit(); //reinitialize list
         }....
          

     function deleteLayerTrash( cid ){
          document.getElementById('ajaxdisabled').style.visibility='visible';
          Seam.Remoting.getContext().setConversationId( cid );
          Seam.Component.getInstance("removeLayerAction").removeLayer(false, rerenderSideBar);
          }

onclick="deleteLayerTrash( #{conversation.id} )"

this quantity of code may be worthless.. this app is so large... it is becoming cumbersome.

The first time this is executed it works fine. It will throw the exception on the second or third execution WITHOUT FAIL.
any direction would be greatly appreciated. 

[tom_goring]

It's worth reading the richfaces manual:

5.4.2. Queue and Traffic Flood Protection
        "eventsQueue" attribute defines the name of the queue that will be used to order upcoming Ajax requests.
        By default, RichFaces does not queue Ajax requests. If events are produced simultaneously, they will come
        to the server simultaneously. JSF implementations (especially, the very first ones) does not guaranty that
        the request that comes first will be served or passed into the JSF lifecycle first. The order how the server
        side data will be modified in case of simultaneous request might be unpredictable. Usage of eventsQueue
        attribute allows to avoid possible mess. Define the queue name explicitly, if you expect intensive Ajax
        traffic in your application.
        The next request posted in the same queue will wait until the previos one is not processed and Ajax
        Response is returned back if the "eventsQueue" attribute is defined. In addition, Richfaces starts to remove
        from the queue "similar" requests. "Similar'"requests are the requests produced by the same event. For
        example, according to the following code, only the newest request will be sent to the server if you type
        very fast and has typed the several characters already before the previous Ajax Response is back.
         ...
               <h:inputText value="#{userBean.name}">
                    <a4j:support event="onkeyup" eventsQueue="foo" reRender="bar" />
               </h:inputText>

[nathandennis]

i cant tell if from the trace... but you may be onto something.

is where a way of Queueing ajax request generated from Seam.Remote?

[nathandennis]

ignore that stupid question... thats the equivalent of asking how do i walk to the store in a bus?

the eventsQueue wasnt actually the source of that exception. it was an array that was not being reinitialized... HOWEVER,, the was the source of many other weird behaviors i was having and your absolutely correct.. i should pay more attention to the manual.

i had read that pharagraph about three months ago, but since i wasnt having problems with such things at the time,,, i guess it didnt register.
five kudos.