RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v50]

[Martin Doerr]

On Wed, 4 Jun 2025 12:56:22 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:
> 
>   Fix build

I've looked over it and couldn't spot any critical issue. I think it's good enough for an experimental feature if we do further cleanups and improvements later.
What I'd like to see as a follow-up is a review of the usage of `Atomic` functions. I've never seen so many of them in such a density.

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Marked as reviewed by mdoerr (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25302#pullrequestreview-2896853345