Threading in JBoss, hibernate + spring
The project I am currently working on has an OM which looks like:
page -> content -> contentFetcher
The page typically has 4 contents (links, toolbars, main and rhs) which are sequentially loaded. This seems like a good candidate for threading; there are no dependencies between them and they are each potentially expensive to created (coming from remote servers etc.).
As an experiment I wrapped added the call to retrieve them in it's own thread and deployed. Unfortunately it all went horribly wrong….and (I think) it is because we are using spring OSIV which creates a single session for the entire thread. The stack trace is:
java.util.ConcurrentModificationException at java.util.HashMap$HashIterator.nextEntry(HashMap.java:787) at java.util.HashMap$ValueIterator.next(HashMap.java:817) at org.hibernate.pretty.Printer.toString(Printer.java:90) at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListen er.java:97) at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:26) at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1009) at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:356) at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106) at org.springframework.orm.hibernate3.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:584)
which is a shame.
(As an aside, it is OK to create threads within JBoss, or rather to retrieve threads from a custom threadpool; thus allowing JBoss to shut down without your threads holding anything up.)
I am sure I can work around this, and I have only spent 5 minutes on this so far, but I don't think we will be able to use SessionPerView…..