9 May
2012
9 May
'12
3:18 p.m.
On Wed, May 9, 2012 at 12:12 PM, Thomas Mortagne
<thomas.mortagne(a)xwiki.com> wrote:
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Thomas Mortagne
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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:
Actually it could be that Restlet put the same context in all the
request using Context#setCurrent().
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 ? 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/xwi…
[2]
https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwi…
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Thomas Mortagne