In your experience what languages would you say handle async well? Genuinely curious. I’ve only ever done JS professionally for a decade but started branching out into python, rust, and kotlin due to personal projects.
For example, in your typical web application a Goroutine is spawned for every incoming connection. This basically gives you a dedicated runtime for each simultaneous connection. In Node or Python, this would be the equivalent of starting a whole new process for every request. But in Go, there's very little cost to doing it this way.
The advantage is that each connection basically never blocks waiting for another user.
In Node and Python, we talk about handling tens to hundreds of requests per second per server.
In Go, we talk about handling thousands to tens of thousands per second. It's just orders of magnitude more throughput.
See: https://www.fastify.io/benchmarks/
Node is more susceptible to poor code and out of band IO slowing it down, but the V8 runtime itself is cpp and simple services are close to just writing decorators over a cpp webserver. It's obscenely fast and good enough for most purposes.
Not only can write programs that are "async", but you also get easy retries (and other tricks), safe refactorability (because of its Pure FP nature), reliable and painless resource management and some other goodies like STM (Software transactional memory).
It's really that good.
The nice thing about this is... You don't have to care. Haskell is a good enough programming language to just put the platform-specific non-blocking hell APIs in a library and let you write code that looks linear and blocking. If you want more control you can get down to the low level non-blocking APIs, but that's usually not going to be worth the trouble.
Haskell IO is basically as async as Javascript, as in every operation is fully asynchronous, you need to call some foreign function if you want otherwise. Except that you have parallelism and can have concurrency too added if you want.
That said, if you have a physical server, Java is quite good, especially with the upcoming Project Loom improvements. The langspec and vmspec have gotten fat the last 20 years, but at least those documents exist. Plus there is OpenJDK which is a great enabler and calmer of nerves; there's a reason so many alt langs target the JVM, and they are good. Groovy, Clojure, Kotlin, Scala are all first-rate languages, IMHO. And with projects like Quarkus you can more easily build native executables that bundle the JRE and make distribution very Rust-like.
Another environment I like specifically for async operation, but mostly by reputation, is Erlang and it's BEAM VM. Erlang itself is such an interesting language, being dynamic, functional, immutable, without traditional control structures (!) but relying heavily on recursion and pattern matching, and of course the "actor model" and extremely lightweight "processes" was invented here (and promptly ported to elsewhere, as with Akka). It was also created by one of the nicest human beings I've ever experienced, Joe Armstrong, may he rest in peace.
IANALL so YMMV.
I'm not sure what you mean here, but if you refer to OracleJDK here then there is basically only OpenJDK for quite some time now -- OracleJDK is just an (optionally) paid support version of the same codebase. Also, most other vendors are pretty much just tiny patched OpenJDKs also, with some niche exceptions.
Swift's design is made to be good for IO workloads on smaller clients, though it hasn't got as many tools for the other end.