RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v59]

[Markus Grönlund]

On Wed, 4 Jun 2025 19:08:40 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:
> 
>  - Fixed merge error
>  - Add comment regarding Threads_lock

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 633:

> 631: 
> 632: void JfrCPUSamplerThread::allow_signal_handlers() {
> 633:   Atomic::release_store(&_active_signal_handlers, (u4)0);

"allow_signal_handlers" is not the best name for this routine - it suggests that by setting _active_signal_handlers = 0, something is enabled - like an inverted Semaphore. But "signal handlers" are allowed for all W of this value, so the 0 has no bearing on enablement.

Just call it "initialize_active_signal_handler_counter" or whatever.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2127267710