[crac] RFR: 8373687: [CRaC] Add metrics through jcmd [v5]

[Radim Vansa]

On Mon, 22 Dec 2025 20:33:12 GMT, Radim Vansa <rvansa at openjdk.org> wrote:

>> src/hotspot/share/runtime/crac.cpp line 714:
>> 
>>> 712:     // silently ignoring this
>>> 713:     return true;
>>> 714:   }
>> 
>> I think we should at least print a warning in such case. I.e. expose a method for the JCMD code to check for support and print the warning to the JCMD stream if there's none. Then here we should fail in such case.
>> 
>> Same for `record_image_score`.
>
> I agree that an explicit command like `jcmd` should print a warning if part of the command line is ignored, but I don't want any warnings the be emitted when using the `Score` methods. And for that I'd like to keep the symmetry with the `record_image_score`.

I've added the warning, but there's no simple way to test: all engines support metrics & labels.

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PR Review Comment: https://git.openjdk.org/crac/pull/281#discussion_r2641262252