graalvm-reachability-metadata VS Graal

gcj had a lot of problems beyond needing configuration of reflection metadata. It used a full reimplementation of the standard library, and it was never adopted by the wider Java community being largely just Red Hat's strategy for creating a fully open source Java implementation rather than something offering specific benefits to Java developers. In particular people thought it'd lead to faster code, but GCC was never designed for Java and the results were actually a fair bit slower iirc.

Native image is quite different. With this new release the compiled images can not only be faster than JIT compiled Java (wow) but also use way less memory and start instantly. At a stroke this is resolving one of the biggest complaints people have always had against JVM languages.

And as a consequence you're seeing adoption by the wider community. All the modern Java web frameworks support it now, and there's a metadata repository where it's collected for projects that haven't accepted it upstream yet [1].

[1] https://github.com/oracle/graalvm-reachability-metadata

Yeah, I was able to get it working by adding some custom runtime hints. jOOQ support was recently added to the graalvm-reachability-metadata repo via this issue, so that may make things easier

During native image generation, native-image tool does a static analysis. There are classes which might not get accessed during this static analysis and they get left out in the final artifact. To overcome this some extra information can be provided during build time. Creating this extra metadata is cumbersome. There's an effort to consolidate these metadata information for various 3rd party libraries into a shared github repo https://github.com/oracle/graalvm-reachability-metadata .

GraalVM is truly great stuff.

GraalVM native compilation helps Java in the data center to avoid being a cost sink and to reduce start-up latency. Oracle needs Java to sell enterprise software.

Oracle contributing to OpenJDK may be required for Amazon cooperation (since Amazon is pushing its own JDK build) and probably helps the library ecosystem work towards native compatibility.

Native support for reflection (used in many libraries) requires "reachability metadata), maps of reflective API usage, at build time. Anyone can do it, but enterprise requires authoritative sources. Until authoritative reachability metadata covers the transitive graph of library+version dependencies in enterprise software, GraalVM builds are a PITA.

- https://github.com/oracle/graalvm-reachability-metadata

- latest release: https://medium.com/graalvm/graalvm-22-3-is-here-jdk-19-build...

- graalvm "community" roadmap: https://github.com/orgs/oracle/projects/6

(As a side note: Mark Reinhold has run the JDK team since 1997: is there any comparable example of such stellar leadership for broadly-adopted software across multiple technical and organizational eras?)

Also, reflection is supported in AOT mode. The analysis, however, does require reachability metadata in some cases. In the best case, libraries provide and maintain appropriate configuration for this. Reachability metadata can also be shared via https://github.com/oracle/graalvm-reachability-metadata.

Most JVM libraries will require some amount of reflection for all frameworks as well, and for that we have made the bet to invest on a JVM wide effort -> https://github.com/oracle/graalvm-reachability-metadata.

The first issue should be solvable by refining Kotlin hints in https://github.com/oracle/graalvm-reachability-metadata that is used for non Spring hints with Boot 3.

Contrary to what vocal Kotlin advocates might believe, Kotlin only matters on Android, and that is thanks to Google pushing it no matter what.

https://spectrum.ieee.org/the-top-programming-languages-2023

https://snyk.io/reports/jvm-ecosystem-report-2021/

And even so, they had to conceed Android and Kotlin on their own, without the Java ecosystem aren't really much useful, thus ART is now updatable via Play Store, and currently supports OpenJDK 17 LTS on Android 12 and later devices.

As for your question regarding numbers, mostly Java 74.6%, C++ 13.7%, on the OpenJDK, other JVM implementations differ, e.g. GraalVM is mostly Java 91.8%, C 3.6%.

https://github.com/openjdk/jdk

https://github.com/oracle/graal

Two examples from many others, https://en.wikipedia.org/wiki/List_of_Java_virtual_machines

Pkl was built using the GraalVM Truffle framework. So it supports runtime compilation using Futurama Projections. We have been working with Apple on this for a while, and I am quite happy that we can finally read the sources!

https://github.com/oracle/graal/tree/master/truffle

Disclaimer: graalvm dev here.

That's pretty interesting. It's not as aggressive as Bee sounds, but the Espresso JVM is somewhat similar in concept. It's a full blown JVM written in Java with all the mod cons, which can either be compiled ahead of time down to memory-efficient native code giving something similar to a JVM written in C++, or run itself as a Java application on top of another JVM. In the latter mode it obviously doesn't achieve top-tier performance, but the advantage is you can easily hack on it using all the regular Java tools, including hotswapping using the debugger.

When run like this, the bytecode interpreter, runtime system and JIT compiler are all regular Java that can be debugged, edited, explored in the IDE, recompiled quickly and so on. Only the GC is provided by the host system. If you compile it to native code, the GC is also written in Java (with some special conventions to allow for convenient direct memory access).

What's most interesting is that Espresso isn't a direct translation of what a classical C++ VM would look like. It's built on the Truffle framework, so the code is extremely high level compared to traditional VM code. Details like how exactly transitions between the interpreter/compiled code happen, how you communicate pointer maps to the GC and so on are all abstracted away. You don't even have to invoke the JIT compiler manually, that's done for you too. The only code Espresso really needs is that which defines the semantics of the Java bytecode language and associated tools like the JDWP debugger protocol.

https://github.com/oracle/graal/tree/master/espresso

This design makes it easy to experiment with new VM features that would be too difficult or expensive to implement otherwise. For example it implements full hotswap capability that lets you arbitrarily redefine code and data on the fly. Espresso can also fully self-host recursively without limit, meaning you can achieve something like what's described in the paper by running Espresso on top of Espresso.

I'm also using GraalVM if that's of any help.

Quarkus is one of Java frameworks for microservices development and cloud-native deployment. It is developed as container-first stack and working with GraalVM and HotSpot virtual machines (VM).

Apologies, I didn't mean to imply DCEVM went poof, just that I was sad it didn't make it into OpenJDK so one need not do JDK silliness between the production one and the "debugging one" since my experience is that's an absolutely stellar way to produce Heisenbugs

And I'll be straight: Graal scares me 'cause Oracle but I just checked and it looks to the casual observer that it's straight-up GPLv2 now so maybe my fears need revisiting: https://github.com/oracle/graal/blob/vm-23.1.0/LICENSE

> to be compiled to a single executable is a strength that Java does not have

I think this is very outdated claim: https://www.graalvm.org/

https://github.com/oracle/graal/issues/7182