[WICKET-3876] Improve synchronization in AsynchronousDataStore buffer structure

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.5-RC5.1
• Fix Version/s: 1.5-RC6
• Component/s: wicket
• Assignee: Martin Tzvetanov Grigorov
• Reporter: Martin Tzvetanov Grigorov
• Created: 06/Jul/11 13:15
• Updated: 12/Jul/11 12:10
• Resolved: 12/Jul/11 12:10

Description

On heavy load we saw the following exception in the logs:

java.lang.NullPointerException
org.apache.wicket.pageStore.AsynchronousDataStore.removeData(AsynchronousDataStore.java:192)
org.apache.wicket.pageStore.DefaultPageStore.removePageData(DefaultPageStore.java:104)
org.apache.wicket.pageStore.DefaultPageStore.unbind(DefaultPageStore.java:149)
org.apache.wicket.page.PageStoreManager.sessionExpired(PageStoreManager.java:407)
org.apache.wicket.Application.sessionUnbound(Application.java:474)
org.apache.wicket.protocol.http.WebApplication.sessionUnbound(WebApplication.java:456)
org.apache.wicket.session.HttpSessionStore$SessionBindingListener.valueUnbound(HttpSessionStore.java:415)
org.apache.catalina.session.StandardSession.removeAttributeInternal(StandardSession.java:1788)
org.apache.catalina.session.StandardSession.expire(StandardSession.java:866)
org.apache.catalina.session.StandardSession.expire(StandardSession.java:740)
org.apache.catalina.session.StandardSession.invalidate(StandardSession.java:1253)
org.apache.catalina.session.StandardSessionFacade.invalidate(StandardSessionFacade.java:186)
org.apache.wicket.session.HttpSessionStore.invalidate(HttpSessionStore.java:177)
org.apache.wicket.Session.destroy(Session.java:492)
org.apache.wicket.Session.invalidateNow(Session.java:504)
org.apache.wicket.Session.detach(Session.java:645)
org.apache.wicket.request.cycle.RequestCycle.onDetach(RequestCycle.java:543)
org.apache.wicket.request.cycle.RequestCycle.detach(RequestCycle.java:477)
org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:255)
org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:160)
org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:216)
....

The buffer structure "entries" may be emptied by one worker thread and tried to be emptied in another...