RFR: 8342818: Implement CPU Time Profiling for JFR [v10]

[Johannes Bechberger]

On Wed, 6 Nov 2024 10:11:18 GMT, Johannes Bechberger <jbechberger at openjdk.org> wrote:

>> Whether the racing is an issue only you can answer. My concern is that using the `Threads_lock` is bad and unnecessary - if you want a stable set of threads then you just need a `ThreadsListIterator`.
>> 
>> Otherwise you'd implement with a safepoint VM operation that you submit to the VMThread.
>
> I just looked into it. We only call the methods that take the locks when
> - the sampler is first enrolled
> - the timer intervals are updated
> - the timer is stopped
> 
> This shouldn't happen that often in practice, so I think that it is good to have the additional guarantees offered by safepoints.
> 
> We can modify this if we see real world performance issues.

So maybe we do timer init and removal at global safepoints?

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PR Review Comment: https://git.openjdk.org/jdk/pull/20752#discussion_r1830813096