9 May
2012
9 May
'12
3:37 p.m.
On Wed, May 9, 2012 at 3:32 PM, Fabio Mancinelli
<fabio.mancinelli(a)xwiki.com> wrote:
On Wed, May 9, 2012 at 3:18 PM, Marius Dumitru Florea
<mariusdumitru.florea(a)xwiki.com> wrote:
Either it's a Restlet bug that should be fixed or we should use
Execution context IMO.
On Wed, May 9, 2012 at 12:12 PM, Thomas Mortagne
<thomas.mortagne(a)xwiki.com> wrote:
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. 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.
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).
-Fabio
--
Thomas Mortagne
Thanks,
Marius
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> * 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…
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--
Thomas Mortagne
--
Thomas Mortagne
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