Graal Native Image

[jwharm]

Graal Native Image for JDK 24 has experimental support for the FFM API: https://www.graalvm.org/jdk24/reference-manual/native-image/native-code-interoperability/foreign-interface/ It would be nice if java-gi would support this. To make it work, the java-gi bindings generator must generate a GraalVM “ForeignRegistrationFeature” class that registers all downcall and upcall FunctionDescriptiors used in the module.

Notes:

• Use command-line arguments -H:+UnlockExperimentalVMOptions and -H:+ForeignAPISupport
• Upcalls in Native Image currently only work on Linux.
• Custom GObject class registration uses reflection intensively, so that will probably not work.

[JFronny]

In my experience with my own libraries, most cases of reflection can also be covered by an annotation processor, which makes native image easier and means less magic, which I think is cleaner. At a minimum, an AP seems like a good fit for GtkTemplate (potentially in combination with a ServiceLoader if early discovery is needed)

[jwharm]

I'd love to replace the reflection code with an annotation processor 🙂 With early discovery, do you mean that it could be used to register Java classes as GTypes during startup? That would be really useful.

[JFronny]

Exactly. An annotation processor can output resource files, which includes the resource files used for the service loader mechanism. This is what AutoService is built on, for example. At runtime, a different component can then invoke the service loader to automatically discover the classes the annotation processor registered. You can even use the AP to generate a glue class that performs the actual registration and register that instead, which makes this more resilient by not relying on no-arg constructors in user code to generate instances.

[jwharm]

Yes the "glue class" would call GObjects.typeRegisterStaticSimple(), GObjects.typeAddInterfaceStatic() etc with the correct names, types and properties from the annotated class.

Using a ServiceLoader for this is really neat. I've been looking at Classgraph to scan the classpath for GObject-derived classes, but a ServiceLoader is just perfect for this.