On Tue, May 8, 2012 at 7:12 PM, Marius Dumitru Florea <[email protected]> wrote: > Hi Fabio and devs, > > I found a serious concurrency issue in the REST server module while > debugging the instability of the Extension Manager when > extensions.xwiki.org repository is used (default case) . The Extension > Manager UI searches extensions using REST and very often it gets 500 > HTTP response code. See http://jira.xwiki.org/browse/XWIKI-7773 for > instance. The server log from xwiki.org shows that the real cause is: > > May 8, 2012 5:09:14 PM org.restlet.engine.application.StatusFilter doHandle > WARNING: Exception or error caught in status service > java.util.ConcurrentModificationException > at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372) > at java.util.AbstractList$Itr.next(AbstractList.java:343) > at > org.xwiki.rest.XWikiSetupCleanupFilter.afterHandle(XWikiSetupCleanupFilter.java:73) > > See the full stacktrace http://pastebin.com/hnFSuwem . > > The problem is related to the way "releasable components" are managed. > I debugged locally both XWikiSetupCleanupFilter [1] and > ComponentsObjectFactory and here's what I discovered: > > * org.restlet.Context.getCurrent() is shared across HTTP requests
What I don't understand is that the Context is stored in a ThreadLocal (see org.restlet.Context) so I don't see how it can be shared across HTTP requests. Or maybe it's reused by two consecutive requests ? > * as a consequence, restlet context attributes are shared across HTTP request > * RELEASABLE_COMPONENT_REFERENCES context attribute is thus also shared > * while a thread iterates this list in XWikiSetupCleanupFilter another > thread can add a component to the list in ComponentsObjectFactory > * the list grows indefinitely because XWikiSetupCleanupFilter only > releases the components; it doesn't remove them from the list > * older instances are re-released > * since the list keeps references to older instances these instances > can't be garbage collected > > Could someone more knowledgeable on the REST module (especially > Restlet) review my findings? > > Thanks, > Marius > > [1] > https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwiki-platform-rest/xwiki-platform-rest-server/src/main/java/org/xwiki/rest/XWikiSetupCleanupFilter.java > [2] > https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwiki-platform-rest/xwiki-platform-rest-server/src/main/java/org/xwiki/rest/ComponentsObjectFactory.java > _______________________________________________ > devs mailing list > [email protected] > http://lists.xwiki.org/mailman/listinfo/devs -- Thomas Mortagne _______________________________________________ devs mailing list [email protected] http://lists.xwiki.org/mailman/listinfo/devs
