Reactive REST Client breaks Hibernate Reactive Transactions

Describe the bug

When combining the Reactive REST client with Hibernate Reactive, the Reactive REST client seems to break Context Propagation, leading to Hibernate Transactions not working as intended.

Expected behavior

Using Reactive REST Client does not have any negative effects on Hibernate Reactive

Actual behavior

Using Reactive REST Client will break Hibernate Reactive Transactions because a call to sessionFactory.withSession() within an existing transaction will result in a new session being created instead of re-using the previously existing session residing in context.

How to Reproduce?

Reproducer: https://github.com/markusdlugi/hibernate-reactive-with-transaction (don’t get confused by the naming)

Steps to reproduce the behavior:

1. Run the application
2. Open http://localhost:8080/test. It will fail with java.lang.IllegalStateException: Couldn't find author 1
3. Remove the REST call (TestResource line 48). If you repeat the test, it will now work, you get an author and some books.
4. Revert your change and add the REST call again. The test will fail again.
5. Remove the Hibernate Transaction by replacing .withTransaction((session, tx) in line 43 with .withSession(session. The test will now work again, even though the REST call is still in place.

It seems like after the REST call, the session2 in the reproducer is not the same session as session1 where the entity was initially persisted. This leads to the error. Seems like the Reactive REST client messes up the context propagation.

Not sure why the example works when getting rid of the transaction entirely, though.

Output of uname -a or ver

Microsoft Windows [Version 10.0.18363.1556]

Output of java -version

OpenJDK 64-Bit Server VM Corretto-11.0.10.9.1 (build 11.0.10+9-LTS, mixed mode)

GraalVM version (if different from Java)

N/A

Quarkus version or git rev

2.0.3.Final

Build tool (ie. output of mvnw --version or gradlew --version)

Apache Maven 3.6.3

Additional information

Possibly related to #16949? But this one seems more severe because you cannot mix Hibernate Reactive Transactions and the REST client at all.

[FroMage]

Actually, we get notified from the client on a VertxThread which has a non-null context, and then from that thread, we grab a random EventLoop thread instead of using the one we are on https://github.com/quarkusio/quarkus/blob/2.1.0.Final/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/RestClientRequestContext.java#L205 (remember there are one event loop thread per CPU) and execute the callback on that thread, which does not have a context. So it looks like our bug after all.

[FroMage]

https://github.com/quarkusio/quarkus/pull/19225