It is worth noting that afterCompletion is a best effort invocation too. Of course you're supposed to try to call them for all registered synchronizations, but if they aren't delivered (or are ignored), they'll have no impact on the transaction outcome anyway. Synchronizations are required to be implemented to cope with afterCompletion not being delivered anyway.
David Lloyd wrote:
Are we sure that we need afterCompletion synchronization processing to be executed in terms of the root controller? The only time I can imagine it mattering is if it is controlling some resource that is outside of the JVM, outside of the transaction, and yet visible to other participants. If synchronizations are used for the purpose of discovering the overall outcome of the transaction, then executing on the local node achieves that purpose. Same thing if the purpose is to clean up some per-VM resource. And I think these two use cases are by far the predominant ones.