Spring Document that @Transactional does not propagate to new threads

When you make a new thread in the method enclosed by @Transactional, transaction does not propagate to the new thread.

For example, in the below case, write1 will rollback but write2 won't.

@Transactional
public void methodA() {
  write1();
  CompletableFuture.runAsync(() -> write2(), Executors.newSingleThreadExecutor());
  if (true) {
    throw new RuntimeException();
  }
}

We need to make clear whether this is the specification or the bug.

Reference: Spring Transaction Management Over Multiple Threads

Comment From: sbrannen

When you make a new thread in the method enclosed by @Transactional, transaction does not propagate to the new thread.

This is by design: Spring's transaction support synchronizes transactional resources for the current thread via a ThreadLocal variable (and not via an InheritableThreadLocal).

Thus, the behavior you have encountered is expected and hinted at in a few places in the reference manual; however, we could make this more explicit.

In light of that, I am making this a "documentation" issue for 5.3.

Comment From: kanjih

That's cool, thanks!

Comment From: rohitp27

@sbrannen Is there a specific place where one must document such a behaviour?

From my understanding it would make the most sense to have it as a point-of-information in the transaction strategies section (Docs link). However, there is a specific reference to ThreadLocal in the hibernate transaction-management strategies section in the same doc (Docs link).

I'd like to take this up if possible. Even if not, I'd appreciate some documentation-practices guidance regarding the above question.

Comment From: sbrannen

@rohitp27, to be honest, I'd have to read through all the documentation we have on transaction management in order to determine where best to document it.

However, I imagine we'd want to add a NOTE in the introductory section in the reference manual and potentially cross reference that note from other relevant sections of the reference manual, and we'd likely want to add a similar note to the Javadoc for @Transactional.

Comment From: stahloss

What if someone would want to be able to multithread within a transaction? I'd definately like to be able.