ConcurrentModificationException upon committing transaction with Hibernate

Question

In our application we have upgraded from Hibernate 3.5.6-final to 4.2.21.Final and now we are getting a ConcurrentModificationException when a database transaction is committed:

java.util.ConcurrentModificationException: null
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
    at java.util.ArrayList$Itr.next(ArrayList.java:851)
    at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:386)
    at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:304)
    at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:349)
    at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:56)
    at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1195)
    at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:404)
    at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101)
    at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:175)

Is this a known issue with Hibernate 4.2?

Answer 1

The exception turned out to be caused by a problem with a Hibernate custom constraint validator we use. The validator's isValid was running a Hibernate criteria query. The query triggered a Hibernate session flush which resulted in the ConcurrentModificationException. We fixed the problem by temporarily disabling auto flush in the isValid method:

@Override
public boolean isValid(Object object, final ConstraintValidatorContext c) {
   try {
      sessionFactory.getCurrentSession().setFlushMode(FlushMode.MANUAL);
      ...
   } finally {
      sessionFactory.getCurrentSession().setFlushMode(FlushMode.AUTO);
   }
}

The problem may also manifest itself as a StackOverflowError.