RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v26]

[Markus Grönlund]

On Sun, 1 Jun 2025 07:26:19 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 two additional commits since the last revision:
> 
>  - Refactoring
>  - Remove convoluted native trace logic

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 557:

> 555:   if (!check_state(jt) ||
> 556:       jt->is_JfrRecorder_thread()) {
> 557:       queue.increment_lost_samples();

is_JfrRecorder_thread() will not appear here since it's excluded and would have returned nullptr from get_java_thread_if_valid().

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 558:

> 556:       jt->is_JfrRecorder_thread()) {
> 557:       queue.increment_lost_samples();
> 558:       tl->set_do_async_processing_of_cpu_time_jfr_requests(false);

Why is this restored here?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119142346
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2119142510