[pron]

OpenJDK's new GC doesn't require STW pauses, the JDK offers preemptive scheduling for millions of threads as well as supervision trees -- although, to be fair, these are recent changes that have, at least in part, been inspired by Erlang. All that is on top of one of the world's most capable compilers. I have long admired Erlang and its passionate community as well as how much they've been able to accomplish (and, as a VM engineer, studied its design), but between passion and being an actual top-tier competitor there's a certain reality gap.

[weatherlight]

To be a competitor, to be fair, implies there's competition. ¯\_(ツ)_/¯.

There's no world, where I'd allow for some future developer to write some Java on the same VM as my Erlang/Elixir code and risk the entire VM crashing.

JVM and Erlang's VM cater to different needs and programming paradigms. While they might share some features or learn from each other's innovations, they are not direct competitors but rather address unique use cases and development requirements.

People who want Erlang are going to reach for Erlang/OTP. People who want Scala/Akka/Java-monolith will leverage the JVM.

Replatforming, doesn't happen often.

No one is hopping from one platform for the other.

[pron]

What do you mean by "the entire VM crashing"? The JVM is no more susceptible to crashes than BEAM.

BTW, my point is that can now be a very good platform for Erlang/OTP. Its performance will allow Erlang/Elixir programs to reduce their reliance on native code and to handle higher loads.

[weatherlight]

It's my understanding the state of the art in observing JVM-based applications is a combination of using thread dumps, gc logs, thread activity visualizations. Thread dumps give us a snapshot of the the name of the thread, its current running state (waiting, blocked, etc), and the stacktrace of the work its currently doing. GC logs give you a record of when and how much garbage was collected and Thread activity visualizations show you the timeline of thread moving between different running states.

The BEAM gives you the ability to see the bottlenecks in your system, via the REPL (in real time!)

It has world-class introspection built in that gives you the power to observe and manipulate your running application through a REPL.

The BEAM has hundreds of features like this, because the BEAM is more of an OS than and VM.

I get it, you're a JVM expert, but the BEAM is more than a check list of optimizations that on paper the JVM can do.

I strongly suggest, before the next time you comment on an BEAM VM vs.JVM debate, please consider watching https://www.youtube.com/watch?v=JvBT4XBdoUE, "The Soul of Erlang and Elixir • Sasa Juric • GOTO 2019"

and reading https://github.com/happi/theBeamBook " an attempt to document the internals of the Erlang runtime system and the Erlang virtual machine known as the BEAM."

Best of luck!

[pron]

You can do all that with the JDK, too, and at higher performance.

As an Erlang fan for many, many years, I am quite familiar with BEAM's design (and why I think Erlang would gain a lot by running on the JVM (or, more precisely, from implementing BEAM and OTP on top of the JVM). Aside from implementation details -- the JDK has simply had a lot more work put into it -- the main difference between the two is that BEAM is higher level, and the runtime itself does more things out of the box, while the JVM is lower level and you can do more in libraries (with no loss of performance, because Java is compiled to very efficient machine code).

Not only would Erlang and Elixir gain better performance and be able to reduce application's reliance on NIFs, but maintaining and evolving them would require less effort.

There is now (as of JDK 19, released six months ago) no capability offered by BEAM -- including runtime manipulation of code through a REPL -- that couldn't be implemented at least as efficiently as a library on top of the JDK. You can see the API here: https://docs.oracle.com/en/java/javase/20/docs/specs/jvmti.h...

[vips7L]

> The BEAM gives you the ability to see the bottlenecks in your system, via the REPL (in real time!)

The JVM has done this forever via VisualVM and more recently via Flight Recorder and Mission Control.

[weatherlight]

In a repl, in a terminal, with no reliance on the OS, with just text. so no the JVM doesn’t do this. It’s not the same.

[vips7L]

You’re moving the goal post. The JVM does provide real time observability into your application.

Personally I think in a terminal with just text is inferior to a proper gui tool. If you really want this jcmd can convert jfr data into different formats that you then can script against.

[pron]

You can write a library/tool that does exactly that, and the JVM offers an API precisely for that purpose. The reason such a tool isn't offered out of the box is that it trades off performance. For example, the JIT can optimise a variable or even an entire object away. When you want to inspect them at runtime, this would trigger a "deoptimization", where the representation would go back to the original bytecode from the optimised machine code. Observability that doesn't trigger deoptimization is, therefore, encouraged, but everything is available.

[weatherlight]

The JVM has 9 9s of reliability? Citation needed please.

[pron]

I don't know what that means. The JVM itself is at least as reliable as BEAM, and probably more so -- it's subject to both more development testing and field testing -- but what needs high reliability is applications. The JVM runs much more critical code than BEAM does, and on a far wider scale and more stressful workloads. The VM itself is the cause of neither Java's reliability nor Erlang's. It's the programming model that matters. The JVM can now support the Erlang model at least as well -- and, I claim, significantly better -- than BEAM ever could with its limited resources. BEAM's Achilles heel has always been performance. That has harmed Erlang application's reliability, as they need to depend on unsafe native code -- that can crash the entire process -- much more than JVM applications.

[hissssst]

> The VM itself is the cause of neither Java's reliability nor Erlang's. It's the programming model that matters. The JVM can now support the Erlang model

That's a common misconception. There is a huge practical difference between "being able to write share-nothing" and "having whole ecosystem built around it". While you're referring to Erlang running unsafe native code, you're completely ignoring the Java running unsafe Java code. To ensure guarantees like "share nothing" or "restartable processes" Erlang developer just needs to write only Erlang and Java developer needs to carefully pick every dependency and almost always rewrite some of them.

That's the exact reason why Akka didn't replace OTP: you're most likely using the dependency which is not written with Akka, and it might share mutable memory, use global mutable state etc. So, even with possibility of writing Erlang-like software, you most certainly will end up with Frankenstein where some parts are fault tolerant, immutable, functional and reasonable, and some parts are oldschool java 8 bullshit.

Do you know what is the definition of DSL? It is when you write your code in one language and get exception in another. And that's exactly why almost every JVM language (except Java) is a DSL.

You just can't have guarantees Erlang has without rewriting everything with your Akka of the day.

[pron]

I think you misunderstood my point. I wasn't trying to argue for Java over Erlang. The people writing Java will continue writing Java, and people writing Erlang will continue doing that.

I was merely pointing out that at this point, the JVM offers a great platform for Erlang itself, which could both increase its visibility and give it a technological boost. You could have everything be Erlang, top to bottom, with far better performance than BEAM could ever achieve, less work, and better interop with where a lot of people actually are.

There could be some disadvantages but overall I think it would be a great opportunity, and one that Erlang could really use.

> And that's exactly why almost every JVM language (except Java) is a DSL.

Other JVM languages choose to have "exceptions in Java" because it's so much less work for them to use existing libraries and they consider it a small enough price to pay. But even if you want virtually all of it to be Erlang, it would still be less work than BEAM.

You could even control exceptions and stack traces, as that's programmable:

https://docs.oracle.com/en/java/javase/20/docs/api/java.base..., https://docs.oracle.com/en/java/javase/20/docs/api/java.base...()