24 Sep
2014
24 Sep
'14
9:23 a.m.
Hi Thomas,
On 24 Sep 2014 at 08:58:56, Thomas Mortagne
(thomas.mortagne@xwiki.com(mailto:thomas.mortagne@xwiki.com)) wrote:
On Tue, Sep 23, 2014 at 11:48 PM, vincent(a)massol.net
wrote:
The idea is to use this only for special cases (like DB shutdown) since in the majority of
cases the component dependency order would be enough. So in these few cases it’s quite
easy and similar to Macro priority (which hasn’t proved to be a problem so far and is
working well).
Hi devs,
Right now there’s a problem when XWiki is shutdown. This is what currently happens:
2014-09-23 13:54:05,563 [Thread-1] DEBUG o.x.shutdown - Starting XWiki shutdown...
2014-09-23 13:54:05,563 [Thread-1] DEBUG o.x.shutdown - Stopping Database Connection
Pool...
2014-09-23 13:54:05,735 [Thread-1] DEBUG o.x.shutdown - Database Connection Pool has been
stopped
2014-09-23 13:54:10,513 [Thread-1] DEBUG o.x.shutdown - Stopping component
[org.xwiki.localization.wiki.internal.DocumentTranslationBundleFactory]…
2014-09-23 13:54:10,513 [Thread-1] DEBUG o.x.shutdown - Component
[org.xwiki.localization.wiki.internal.DocumentTranslationBundleFactory] has been stopped
…
2014-09-23 13:54:10,514 [Thread-1] DEBUG o.x.shutdown - Stopping component
[org.xwiki.search.solr.internal.DefaultSolrIndexer]...
2014-09-23 13:54:10,514 [Thread-1] DEBUG o.x.shutdown - Component
[org.xwiki.search.solr.internal.DefaultSolrIndexer] has been stopped
…
2014-09-23 13:54:10,539 [Thread-1] INFO o.x.shutdown - XWiki shutdown has been
completed.
As you can see the problem is that the DB is stopped first. So any code accessing the DB
will get an error once the connection pool is stopped. This is why we get a lot stack
traces when you ctrl-c XWiki quickly after it starts (i.e. when the init is not finished
or when SOLR is still indexing). You can also get stack traces if a watchlist is being
sent or some scheduler job is executing for example.
There are 2 ways to fix this:
- solution 1: all code that accesses the DB could check if an XWiki shutdown is in
progress and don’t generate stack traces if this is the case
- solution 2: stop the DB as the last thing, after everything else has stopped
Obviously solution 2 is much better.
I’ve started implementing it by doing this:
- Remove the current HibernateShutdownEventListener since this is executed first during
shutdown, before component disposal
- Instead have XWikiHibernateStore implement Disposable and move the content of
HibernateShutdownEventListener in that method
This works already better but it’s not enough since ECM.dispose() works out the component
dependencies but this works only for explicit dependencies and doesn’t work if a component
uses the ComponentManager to dynamically find implementations (as this is the case for
example for DefaultSolrIndexer).
Thus in order to help the component disposal process, I propose to introduce a new
annotation: @DisposePriority(int).
Note that an alternative would be to introduce a new Disposable interface with a new
getPriority() method in it (we cannot modify the current Disposable since that would break
backward compat).
It's always hard to know what priority to put exactly so this is last
resort solution for me. A few other alternatives:
1) stop the DB after disposing components (I would not vote for it I
think but it should work for this use case)
Yes I thought about this but I wanted something a bit more generic. See at the end of this
email though.
2) introduce something like a @ComponentDependency
annotation to let
component declare indirect dependencies (ECM#dispose would simply add
@ComponentDependency annotations to its current dependencies based
ordering) and:
2.1) even when a component does not directly use XWikiStoreInterface
(pretty much all of them are using XWiki methods and don't even know
about it officially) we could still ask them to declare something like
@ComponentDependency(XWikiStoreInterface.class) to indicate that they
want to be disposed after any component of this role.
Yes I had also thought about this one but discarded because it means finding all
components using indirectly XWikiStoreInterface and modifying them all. This means a lot
of places (since a lot of places use the XWiki class for example) and a lot of work.
I also find it a lot more complex to implement than a priority order which seems really
the most simple solution.
2.2) make XWiki instance a component instead of
storing it in the
servlet context and inject it instead of accessing it through
XWikiContext (XWiki itself would inject the component it want). XWiki
itself would declare a
@ComponentDependency(XWikiStoreInterface.class).
2.3) move all storage related methods from XWiki (saveDocument,
getDocument, etc) to another component (and remove XWikiContext
parameter to all these methods) which would be injected by components
directly instead of searching for the XWikiContext (that's how new
model will work but we can have another one before that still expose
olcore APIs like XWikiDocument). Then this component would take care
of declaring the @ComponentDependency(XWikiStoreInterface.class) (it's
not really possible to directly inject the right XWikiStoreInterface
since it's configuration based)
These 2 alternatives are ok but they are a lot of work and could be done in the future. I
was trying to find a solution that can be applied in 1/2 day right now. We need to fix our
bug now and I fear we’ll just not do anything if we wait for 2.2 and 2.3 (which we can do
on the longer run).
Since you don’t agree about priority and since I’d like to fix the shutdown “bug” for
6.2.x and on 6.3M1 now, I’m proposing the following alternative for now:
* Introduce a new constructor in the ApplicationStoppedEvent
class: ApplicationStoppedEvent(boolean afterDispose)
* Modify XWikiServletContextListener.contextDestroyed() so that it sends the
ApplicationStoppedEvent(false) before calling cm.dispose() and it sends the
ApplicationStoppedEvent(true) after calling cm.dispose()
* Keep HibernateShutdownEventListener but make it listen to ApplicationStoppedEvent(true)
This will ensure it’s called after all components have been disposed.
WDYT? Acceptable?
Thanks
-Vincent
> The idea is then to use this information in
ECM.dispose() to first sort all components based on this and then only to order them with
their dependencies.
>
> WDYT?
>
> Thanks
> -Vincent