Vert.x VS Quasar

https://vertx.io/

It's actively maintained with full time developers, performant, supports Kotlin out of the box, and has more features?

Hibernate Reactive integrates with Vert.x, but an extension allows to bridge to Project Reactor if wanted

Have you looked at Vert.x?

Explicitly so:

I really like Eclipse Vert.x... As both an Erlang dev and Java dev, it's a great synergy and soon to have support for Virtual Threads similar to BEAM.

There are many lean, popular, non-magical libraries in Java land. (https://quarkus.io/, https://vertx.io/, etc). Spring is a monster 😱. Its like comparing Kubernetes (written in Go) with some lean framework in another lang.

Eclipse Vert.x - Add amazing Async to any Java stack

Vert.X example: https://github.com/eclipse-vertx/vert.x/blob/master/src/main/java/examples/EventBusExamples.java#L106 (couldn't even find docs)

In fact, it builds on top of proven standards such as Eclipse MicroProfile or frameworks such as Vert.x or JAX‑RS.

Java 21 doesn't retrofit green threads though. Quasar [0] is a library that implemented fibers for Java and the main developer pron has joined the OpenJDK development team. All that was necessary for first party support is to make the JDK libraries yield when blocking.

Adopting async isn't impossible at all, there is very little demand for it.

[0] https://docs.paralleluniverse.co/quasar/

Third party options have been around for nearly a decade now: https://docs.paralleluniverse.co/quasar/

Quasar Fiber (https://docs.paralleluniverse.co/quasar/) is the equivalent implementation of goroutine in Java.

Even Loom architect Ron Pressler had something else in mind with his earlier prototype Quasar, with a spaceship demo.

I'd say because of Erlang. Loom's architect was building a bytecode-modifying (with a javaagent) lib named Quasar before he joined Oracle. The project page mentions a news titled "Introductory blog post: Erlang (and Go) in Clojure (and Java), Lightweight Threads, Channels and Actors for the JVM." in May 2, 2013.