Embedded j9stubs.jar ?

[laeubi]

Similar to the last question, there is a j9stubs.jar embedded in the equinox, what is it used for? Is equinox actually supposed to be some kind of Multi-Release jar? Is it to prepare for move to java 9+?

[tjwatson]

This is so we can compile in support for shared classes cache when running on Eclipse OpenJ9 Java. We need the com.ibm.oti.shared package to do that. See org.eclipse.osgi.internal.cds package. Also see https://blog.openj9.org/2018/10/30/openj9-shared-classes-with-eclipse-equinox-4-9/

This jar is here so we can continue to compile with hotspot JDK and not require OpenJ9 JDK to compile Equinox.

[tjwatson]

With that said, we could change to using reflection like we do in OpenLiberty: https://github.com/OpenLiberty/open-liberty/blob/integration/dev/com.ibm.ws.kernel.boot.common/src/com/ibm/ws/kernel/boot/classloader/SharedClassCacheHook.java

But I find non-reflection to be much better to understand.

[laeubi]

Thanks for the insights, this seems not so easy to get rid of ...

[laeubi]

@tjwatson one thing that came into my mind. Do you think it would be possible that what currently is j9stubs.jar to be released by the J9 project as a regular maven-artifact?

That way it would be possible to reference that in a maven standard way as a provided dependency without the need to embed the jar, other projects can reuse it and we won't need tycho/pde specific jars.extra.classpath?

[tjwatson]

We could ask, but it would be a little strange in my opinion because I doubt the artifact would be anything that could be useful at runtime. It would have to be a stubbed set of APIs they have for shared classes that is only meant to compile against.

[laeubi]

I doubt the artifact would be anything that could be useful at runtime.

It won't be used at runtime or installed anywhere (provided in maven means = use for compile but it is not a regular dependency but a perquisite of the platform where the artifact runs), similar to the osgi-annotation jars.

It would have to be a stubbed set of APIs they have for shared classes that is only meant to compile against.

Yes exactly that would be the idea, so even OpenLiberty could use this as a provided dependency (or others as well) but dont need to build/host an own stubbed API...

[tjwatson]

We can ask, I'm just not sure they will be up for doing it.

[laeubi]

Can you bring this up? I have absolute no knowledge about J9 and how it works or which people best to ask here and what are the exact demands of Equinox why we need this...

[tjwatson]

I will, not sure on the chances of success. Another option is to compile the stub source as part of the org.eclipse.osg project that we can then compile against but not ship?