On Wed, May 9, 2012 at 3:32 PM, Fabio Mancinelli <[email protected]> wrote: > On Wed, May 9, 2012 at 3:18 PM, Marius Dumitru Florea > <[email protected]> wrote: >> On Wed, May 9, 2012 at 12:12 PM, Thomas Mortagne >> <[email protected]> wrote: >>> On Wed, May 9, 2012 at 11:06 AM, Thomas Mortagne >>> <[email protected]> wrote: >>>> 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 ? >>> >>> 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. >> >> Indeed. >> >> The code that manually releases REST resource components that have a >> per-lookup instantiation strategy looks to me like a workaround for >> the fact that we don't have a per-request (or per-execution) 'release' >> strategy (i.e. components that are automatically released at the end >> of the request/execution). >> > That's exactly this. To avoid memory leaks due to the allocations in > the ComponentsObjectFactory of per-lookup components that would never > be released otherwise. > Re the thread issues, I thought that the context was per-request but > AFAIU from what you're saying it's not the case. > > Maybe we could put a thread local providing the actual list in the > context instead of putting the list directly.
Either it's a Restlet bug that should be fixed or we should use Execution context IMO. > > -Fabio > >> Thanks, >> Marius >> >>> >>>> >>>>> * 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 >>> >>> >>> >>> -- >>> Thomas Mortagne >>> _______________________________________________ >>> devs mailing list >>> [email protected] >>> http://lists.xwiki.org/mailman/listinfo/devs >> _______________________________________________ >> devs mailing list >> [email protected] >> http://lists.xwiki.org/mailman/listinfo/devs > _______________________________________________ > 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
