RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v46]

[Markus Grönlund]

On Wed, 4 Jun 2025 11:28:51 GMT, Johannes Bechberger <jbechberger at openjdk.org> wrote:

>> This is the code for the [JEP 509: CPU Time based profiling for JFR](https://openjdk.org/jeps/509).
>> 
>> Currently tested using [this test suite](https://github.com/parttimenerd/basic-profiler-tests). This runs profiles the [Renaissance](https://renaissance.dev/) benchmark with
>> - ... different heap sizes
>> - ... different GCs
>> - ... different samplers (the standard JFR and the new CPU Time Sampler and both)
>> - ... different JFR recording durations
>> - ... different chunk-sizes
>
> Johannes Bechberger has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Improve error message

I am approving this PR for the following reasons:

1. We have reached a state that is "good enough" - I no longer see any fundamental design issues that can not be handled by follow-up bug fixes.
2. There are still many vague aspects included with this PR, as many has already pointed out, mostly related to the memory model and thread interactions - all those can, and should, be clarified, explained and exacted post-integration.
3. The feature as a whole is experimental and turned off by default.
4. Today is the penultimate day before JDK 25 cutoff. To give the feature a fair chance for making JDK25, it needs approval now.

Thanks a lot Johannes and all involved for your hard work getting this feature ready.

Many thanks
Markus

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Marked as reviewed by mgronlun (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25302#pullrequestreview-2896467191