RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v42]

[Markus Grönlund]

On Tue, 3 Jun 2025 21:56:41 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> Johannes Bechberger has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Rename autoadapt
>
> src/hotspot/share/jfr/periodic/sampling/jfrThreadSampling.cpp line 360:
> 
>> 358:   tl->set_do_async_processing_of_cpu_time_jfr_requests(false);
>> 359:   if (lock) {
>> 360:     tl->acquire_cpu_time_jfr_dequeue_lock();
> 
> This is your synchronization point on return from native code, which is effectively a spinlock. This can cause problems when a large number of threads are being processed by the "do_async_processing" request call.
> 
> We should fix this as a bug after integration (use a proper Monitor as a synchronization point).

Filed: https://bugs.openjdk.org/browse/JDK-8358621

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2127300632