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). 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/xwik... [2] https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwik... _______________________________________________ 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