RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v45]

[Johannes Bechberger]

On Wed, 4 Jun 2025 11:23:57 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> Johannes Bechberger has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 127 commits:
>> 
>>  - Merge branch 'master' into parttimenerd_cooperative_cpu_time_sampler
>>  - Add error message on signal handler install failure
>>  - Fix signal handler synchronization
>>  - Improve
>>  - Rename autoadapt
>>  - Make process_cpu_time_request private and move up
>>  - Reorder condition
>>  - Tiny refactoring
>>  - Restrict threads for which timers are created
>>  - Fix tiny mistake
>>  - ... and 117 more: https://git.openjdk.org/jdk/compare/7838321b...4fd4b673
>
> src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 647:
> 
>> 645:   // install sig handler for sig
>> 646:   if ((s8)PosixSignals::install_generic_signal_handler(SIG, (void*)::handle_timer_signal) == -1) {
>> 647:     log_error(jfr)("Failed to install signal handler for CPU thread sampling, possibly because another profiler is active: %s", os::strerror(os::get_last_error()));
> 
> That we are using a signal handler to provide the user with CPU time information is an implementation detail. Its good to provide an error message, but I think it should reflect back on something the user is expecting.
> 
> Perhaps add a line that says something along the lines of "CPUTimeSample events will not be recorded."

Done

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2126360801