[xwiki-devs] [Proposal] Introduce new @DisposePriority annotation or new Disposable interface to fix XWiki shutdown

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). 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