RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v43]

[Johannes Bechberger]

On Wed, 4 Jun 2025 11:13:30 GMT, Andrei Pangin <apangin at openjdk.org> wrote:

>> Johannes Bechberger has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Improve
>
> src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 238:
> 
>> 236:   tl->cpu_time_jfr_queue().resize_for_period(_current_sampling_period_ns / 1000000);
>> 237:   timer_t timerid;
>> 238:   if (create_timer_for_thread(thread, timerid)) {
> 
> Timer creation failure is not an impossible situation, we should somehow let user know that not all threads are being profiled but without flooding in logs. One warning per profiling session may be a good compromise.
> You can verify failure condition by setting low `ulimit -i`.

I added a "Failed to create timer for a thread" warning

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2126373721