RFR: 8311302: Allow for jlinking a custom runtime without packaged modules being present [v23]

[Severin Gehwolf]

On Wed, 3 Apr 2024 22:31:39 GMT, Mandy Chung <mchung at openjdk.org> wrote:

>> Severin Gehwolf has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Move CreateLinkableRuntimePlugin to build folder
>>   
>>   Keep runtime link supporting classes in package
>>   jdk.tools.jlink.internal.runtimelink
>
> Thanks for the investigation w.r.t. extending jimage.  It does not seem worth the effort in pursuing the support of adding resources to an existing jimage file.   To me, putting the diff data under `lib` directory as a private file is a simpler and acceptable solution.   It allows the second jlink invocation to avoid the plugin pipeline if the per-module metadata is generated in normal jlink invocation.
> 
> (An observation: The current implementation requires the diffs to be generated as a plugin.  For this approach, it may be possible to implement with a separate main class that calls JLink API and generates the diffs.)

> > @mlchung @AlanBateman Any thoughts on this latest version? Is this going into the direction you had envisioned? Any more blockers? The CSR should be up-to-date and is open for review as well. If no more blockers I'll go over this patch once more and clean it up to prepare for integration. Thanks!
> 
> Thanks for all the efforts on this.

Thanks for looking at this, Alan!

> I've looked through the latest version. I'm a little bit comfortable with LinkDeltaProducer. One reason it's build tool that is tied tied to code in the jdk.jlink module, and secondly is that it copies runtime-image-link.delta into the run-time image. Our long standing position is that the run-time image is created by jlink rather than a combination of jlink and extra stuff copied in by the build.
> 
> The part that I like with the current proposal is lib/runtime-image-link.delta as it's less complicated that previous iterations that added a resource into the jimage container.
> 
> What would you (and @mlchung) think of having jlink generate lib/runtime-image-link.delta as a step between the pipeline and image generation?

If I understand you correctly, this would be no longer a build-time only approach to produce the "linkable runtime"? It would be some-kind of jlink-option driven approach (as it would run some code that should only run when producing a linkable runtime is requested)? Other than that, it should be fine as the previous iteration basically did that but at a different phase. Also note that the previous iteration used a build-only jlink plugin so as to satisfy the build-time only approach, yet it ran as part of the plugin-pipeline which wasn't desired either. But it was something similar to what you seem to be describing now. Did I get something wrong?

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PR Comment: https://git.openjdk.org/jdk/pull/14787#issuecomment-2058919838