RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v26]

[Johannes Bechberger]

On Mon, 2 Jun 2025 11:22:45 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> Because we need to add the threads from the signal handler. So any kind of growing array or set would not work, especially if we want to remove the threads from within the signal handler again.
>> 
>> This is certainly an area of future optimization, albeit this doesn't seem to have any measurable performance impact in my renaissance benchmark runs.
>
> I don't understand what allocation has to do with anything. I'm talking about code branch layout to avoid having to test "has_cpu_time_jfr_requests()" when we know it will be false by default.

Ah. Sorry. Is it about reading the atomic boolean flag again?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2120882396