Datatable ConcurrentModificationException

###JSF ConcurrentModificationException on datatable

We had an outage recently, and in the log of our application, we can see this exception. Looks like the data in a table is being modified while primefaces is sorting ¿How is this possible?

This is something that doesn’t happen frequently, it just happened once in a production enviroment. Also this same stack trace repeats like ten or more times in seconds.

I know that it is because some other thread is modifying the list, but I don’t understand why, because it is a simple datatable with a sorting and It happens occasionally.

05-Jul-2022 19:13:53.583 SEVERE [http-nio-8080-exec-746] com.sun.faces.application.view.FaceletViewHandlingStrategy.handleRenderException Error Rendering View[/pages/example.xhtml] java.util.ConcurrentModificationException at java.util.ArrayList.sort(ArrayList.java:1466) at java.util.Collections.sort(Collections.java:177) at org.primefaces.component.datatable.feature.SortFeature.singleSort(SortFeature.java:167) at org.primefaces.component.datatable.DataTableRenderer.preRender(DataTableRenderer.java:141) at org.primefaces.component.datatable.DataTableRenderer.encodeEnd(DataTableRenderer.java:93) at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:949) at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1912) at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1908) at javax.faces.render.Renderer.encodeChildren(Renderer.java:176) at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:918) at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1905) at com.sun.faces.context.PartialViewContextImpl$PhaseAwareVisitCallback.visit(PartialViewContextImpl.java:638) at com.sun.faces.component.visit.PartialVisitContext.invokeVisitCallback(PartialVisitContext.java:183) at javax.faces.component.UIForm.visitTree(UIForm.java:405) at javax.faces.component.UIComponent.visitTree(UIComponent.java:1747) at javax.faces.component.UIComponent.visitTree(UIComponent.java:1747) at com.sun.faces.context.PartialViewContextImpl.processComponents(PartialViewContextImpl.java:423) at com.sun.faces.context.PartialViewContextImpl.processPartial(PartialViewContextImpl.java:342) at org.primefaces.context.PrimePartialViewContext.processPartial(PrimePartialViewContext.java:65) at javax.faces.context.PartialViewContextWrapper.processPartial(PartialViewContextWrapper.java:252) at org.omnifaces.context.OmniPartialViewContext.processPartial(OmniPartialViewContext.java:122) at javax.faces.component.UIViewRoot.encodeChildren(UIViewRoot.java:1124) at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1905) at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:465) at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:194) at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:151) at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:151) at org.omnifaces.viewhandler.OmniViewHandler.renderView(OmniViewHandler.java:155) at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:126) at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:100) at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:223) at javax.faces.webapp.FacesServlet.service(FacesServlet.java:671) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at ar.com.dux.jsf.filters.CacheFilter.doFilter(CacheFilter.java:27) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at ar.com.dux.jsf.filters.SecurityFilter.doFilter(SecurityFilter.java:84) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:89) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.omnifaces.filter.GzipResponseFilter.doFilter(GzipResponseFilter.java:183) at org.omnifaces.filter.HttpFilter.doFilter(HttpFilter.java:108) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:196) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:698) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:364) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:624) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:831) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1650) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:748)

Reproducer

No response

Expected behavior

No response

PrimeFaces edition

Community

PrimeFaces version

8

Theme

Avalon

JSF implementation

Mojarra

JSF version

2.3.9

Browser(s)

Chrome

[fanste]

Edit: Damn, melloware was faster 😉

–

There are two possibe causes for that issue:

1. Multiple threads working on the same list
2. A single thread that modifies the list while iterating over it (e.g. counted for or foreach)

The second option should not be the cause here, as the stacktrace contains just a call to ArrayList.sort. I don’t think, that the JDK is faulty at that place.

The first option is more likely:

• Simultanious AJAX requests - com.sun.faces.context.PartialViewContextImpl.processPartial should be an indication, that this happens during AJAX
• Shared list due to wrong bean scope - e.g. session or even application
• Correct bean scope, but the list comes from a shared source

[melloware]

@marcelocastrillo you can try 1 of 2 solutions.

1. Wrap your backing bean list Collections.synchronizedList…

List<Object> objList = Collections.synchronizedList(new ArrayList<Object>());

1. Try java.util.concurrent.CopyOnWriteArrayList https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/CopyOnWriteArrayList.html it’s expensive to modify, but wait-free to read.