[cheradenine_uk]

I think a lot of people are missing the point.

Go look at the sourcecode. Look at how simple it is - anyone who has created a thread with java knows what's happening. With only minor tweaks, this means your pre-existing code can take advantage of this with, basically, no effort. And it retains all the debuggability of traditional java thread (I.e: a stack trace that makes sense!)

If you've spent any time at all dealing with the horrors of c# async/await (Why am I here? Oh, no idea) and it's doubling of your APIs to support function colouring - or, you've fought with the complexities of reactive solutions in the Java space -- often, frankly, in the name of "scalability" that will never be practically required -- this is a big deal.

You no longer have to worry about any of that.

[pjmlp]

Or inserting the occasional Task.Run() calls, as means to avoiding changing the whole call stack up to Main().

[gavinray]

This hasn't been that much of a problem, IME

If you decide somewhere deep in your program you want to use async operations, most languages allow you to keep the invoking function/closure synchronous and return some kind of Promise/Future-like value

[pjmlp]

Which is exactly the workaround with Task.Run(), being able to integrate a library written with async/await in codebases older than the feature, where no one is paying for a full rewrite.

[bullen]

Agreed it's simpler, but using NIO with one OS thread per core also has it's benefits.

The context switch (how ever small) will cause latency when this solution is at saturation.

I think they should write four tests: fiber, NIO and each with userspace networking (no kernel copying network memory) and compare them.

Why Oracle is stalling removing the kernel for Java networking is surprising to me, they allready have a VM.

[pron]

https://github.com/ebarlas/project-loom-comparison

[vlovich123]

Shouldn’t you be able to send authorization and authentication requests in parallel in the async and virtual threads cases?

[threeseed]

It is just an example so they could do anything.

But in the real world it is common to need information from the authorization stage to use in the authentication stage. For example you may have a user login with an email address/password which you then pass to an LDAP server in order to get a userId. This userId is then used in a database to determine with objects/groups they have access to.

[vlovich123]

A lower latency design would be for the authorization service to be able to work with either. That way those requests could be done in parallel to reduce latency.

[bullen]

Thx, I'm missing bandwidth and latency in those graphs.

[blibble]

there's still a context switch with NIO, you're just doing it manually

[bullen]

The context switches in NIO is between fewer threads, you just need one per core.

Memory contention is also playing into this.

The benchmark they made is asking the question in a way that it leans into the answer they need, just like 99% of all human activity it's biased.

[blibble]

you're missing the point and taking "context switch" literally

with NIO you are still managing the stack, just yourself instead of letting the operating system do it for you

it is still a "context switch", just done in your code instead of the OS

and that's not free (and likely more expensive than saving and restoring a set of registers)

[SemanticStrengh]

Except Kotlin coroutines already works, can be very easily integrated in existing java codebases and are much superior than loom (structured concurrency, flow, etc)

[richdougherty]

Kotlin coroutines are amazing. They're built on very clever tech that converts fairly normal source code into a state machine when compiled. This has huge benefits and allows the programmer to break their code up without the hassle of explicitly programming callbacks, etc.

https://kotlinlang.org/spec/asynchronous-programming-with-co...

However... an unavoidable fact is that converted code works differently to other code. The programmer needs to know the difference. Normal and converted code compose together differently. The Kotlin compiler and type system helps keep track, but it can't paper over everything.

Having lightweight thread and continuations support directly in the VM makes things very much simpler for programmers (and compiler writers!) since the VM can handle the details of suspending/resuming and code composes together effortlessly, even without compiler support, so it works across languages and codebases.

I don't want to be critical about Kotlin. It's amazing what it achieves and I'm a big fan of this stuff. Here are some notes I wrote on something similar, Scala's experiments with compile-time delimited continuations: https://rd.nz/2009/02/delimited-continuations-in-scala_24.ht...

I think this is a general principle about compiler features vs runtime features. Having things in the runtime makes life a lot easier for everyone, at the cost of runtime complexity, of course.

Another one I'd like to see is native support for tail calls in Java. Kotlin, Scala, etc have to do compile-time tricks to get basic tail call support, but it doesn't work across functions well.

Scala and Kotlin both ask the programmer to add annotations where tail calls are needed, since the code gen so often fails.

https://kotlinlang.org/docs/functions.html#tail-recursive-fu...

https://www.scala-lang.org/api/3.x/scala/annotation/tailrec....

https://rd.nz/2009/04/tail-calls-tailrec-and-trampolines.htm...

As a side note, I can see that tail calls are planned for Project Loom too, but I haven't heard if that's implemented yet. Does anyone know the status?

"Project Loom is to intended to explore, incubate and deliver Java VM features and APIs built on top of them for the purpose of supporting easy-to-use, high-throughput lightweight concurrency and new programming models on the Java platform. This is accomplished by the addition of the following constructs:

* Virtual threads

* Delimited continuations

* Tail-call elimination"

https://wiki.openjdk.java.net/display/loom/Main

[SemanticStrengh]

Coroutines are much less coloured than async await programming though since functions returns resolved types directly instead of futures. But yes there is the notion of coroutine scope but I don't see how to supress it without making it less expressive.

Very few people know it but Oracle is developping an alternative to Loom, in parallel. https://github.com/oracle/graal/pull/4114

BTW i expect Kotlin coroutines to leverage loom eventually.

As for the tailrecursive keyword, it is not a constraint but a feature since it guarantee at the type level that this function cannot stack overflow. Few people know there is an alternative to tailrecursive, that can make any function stackoverflow safe by leveraging the heap via continuations https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-deep-re...

As for Java, there is universal support for tail recursion at the bytecode level https://github.com/Sipkab/jvm-tail-recursion

[gavinray]

Thanks for posting that link to Java tail recursion library, super handy + didn't know about it. You need tail recursion for writing expression evaluators/visitors frequently.

I've been using an IntelliJ extension that can do magic by rewriting recursive functions to stateful stack-based code for performance, but it spits out very ugly code:

https://github.com/andreisilviudragnea/remove-recursion-insp...

  > "This inspection detects methods containing recursive calls (not just tail recursive calls) and removes the recursion from the method body, while preserving the original semantics of the code. However, the resulting code becomes rather obfuscated if the control flow in the recursive method is complex."

It was this guy's whole Bachelor thesis I guess:

https://github.com/andreisilviudragnea/remove-recursion-insp...

[ohgodplsno]

> Coroutines are much less coloured than async await programming though since functions returns resolved types directly instead of futures

Only because the compiler does its magic behind the scenes and transforms it into bytecode that takes a lambda with a continuation. Try calling a suspend function from java or starting a job and surprise, it's continuations all the way down

[SemanticStrengh]

yes interfacing with java is generally made via RxJava and reactor. Interfacing is easy but yes nobody wants to use rxjava and reactor in the first place.. I wonder wether loom will enable easier interop and make the magic work from java side POV

[richdougherty]

> Coroutines are much less coloured

I think another commenter pointed out that they are still coloured though. Still, they're very cool - and you can use them for more than just lightweight threading.

> As for the tailrecursive keyword, it is not a constraint but a feature since it guarantee at the type level that this function cannot stack overflow

I'd say tailrecursive is compiler feature (codegen the recursion into a loop) to work around a runtime contraint (no tail call optimisation).

The lack of tail call optimisation on the JRE means recursion is a lot less safe than in functional language runtimes which guarantee stacks don't overflow when you make tail calls.

> As for Java, there is universal support for tail recursion at the bytecode level.

Just a note here for other readers that there are several terms in play here.

I was talking about "tail calls" - when a function calls a function as its last operation - and I mentioned some annotations to do "tail recursion", which is a special case - when a function calls _itself_ as its last operation.

SemanticStrength is talking about "tail recursion" only here. The JVM bytecode can support tail recursion (tail calls on the same method), since we can use the same bytecode that is used for while loops, etc.

However, we cannot do safe tail recursion between different functions (yet), in the same way that we cannot have a loop spanning more than one function. Tail call optimisation is something that will hopefully come in Project Loom.

[kaba0]

Doesn’t it possibly get inlined by current mechanisms as well?

[richdougherty]

Can you explain a bit more?