Re: [xwiki-devs] Concurrency issue in REST server module

On Wed, May 9, 2012 at 11:06 AM, Thomas Mortagne <thomas.mortagne(a)xwiki.com> wrote: > On Tue, May 8, 2012 at 7:12 PM, Marius Dumitru Florea > <mariusdumitru.florea(a)xwiki.com> 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 ? Actually it could be that Restlet put the same context in all the request using Context#setCurrent().

We should maybe use the XWiki Execution context which has been made for use cases like that to be safe.

> >> * 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/xwi… >> [2] https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwi… >> _______________________________________________ >> devs mailing list >> devs(a)xwiki.org >> http://lists.xwiki.org/mailman/listinfo/devs > > > > -- > Thomas Mortagne -- Thomas Mortagne _______________________________________________ devs mailing list devs(a)xwiki.org http://lists.xwiki.org/mailman/listinfo/devs