Re: [jboss-as7-dev] JTA Synchronization.afterCompletion callback can occur in a background thread but JPA EntityManager must be accessed in single-threaded manner...

Well the problem is TX boundaries typically are the lifespan of the request, so the application thread would never fully give up control. The only thing you can really without relying on checks, or deferring to the db/tm, is to interrupt the application thread from the sync thread. However the EntityManager would have to be carefully coded to process thread interruption in a way that distinguishes between tx timeout and user requested interrupt. It's probably the same amount of code either way.