RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v5]

[Markus Grönlund]

On Fri, 23 May 2025 21:20:39 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 one additional commit since the last revision:
> 
>   Fix compilation

src/hotspot/share/jfr/support/jfrThreadLocal.hpp line 103:

> 101:   volatile CPUTimeLockState _cpu_time_jfr_locked = UNLOCKED;
> 102:   volatile bool _has_cpu_time_jfr_requests = false;
> 103:   JfrCPUTimeTraceQueue _cpu_time_jfr_queue{0};

Please initialize these fields in the initializer list, like the other fields.

Also, what capacity will the JfrCPUTimeTraceQueue have with an initializer like the above - {0}? In GDB i see that the capacity is 10000. Each element is 48 bytes, meaning each thread now has an associated queue of 468 kb, almost 0.5 Mb. Is that correct?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2105860988