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

[Johannes Bechberger]

On Wed, 4 Jun 2025 13:47:01 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

>> Johannes Bechberger has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix build
>
> src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 430:
> 
>> 428: void JfrCPUTimeThreadSampling::create_sampler(double rate, bool auto_adapt) {
>> 429:   assert(_sampler == nullptr, "invariant");
>> 430:   _sampler = new JfrCPUSamplerThread(rate, auto_adapt);
> 
> If we start a recording on an already running process we have a race here where a new thread can create and set its timer before we call init_timers() where the signal handler is installed. In that case the program will terminate with message “Profiling timer expired" (default action for SIGPROF). It can be easily reproduced by adding a delay here and starting a recording on a simple test that just creates new threads. We need to add some extra check in create_timer_for_thread() or install the signal handler earlier.

I created a `has_timer` flag that is checked by `create_timer_for_thread()` before creating timers and set by `init_timers`. Is this what you envisioned?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2126783367