RFR: 8342818: Implement CPU Time Profiling for JFR [v4]

[Johannes Bechberger]

On Wed, 6 Nov 2024 13:47:36 GMT, Johannes Bechberger <jbechberger at openjdk.org> wrote:

>> That is both interesting (and worrying). I'm going to write a test for the latter issue.
>
>> NoHandleMark will not work with with continuations. Please see how we do it in JfrStackTrace::record()
> 
> Thank you.
> 
>> This indicates that the event is turned on, despite "enabled" being false. Is there a bug in the control / enable setting mechanism?
> 
> I was unable to reproduce the issue but I removed the control attribute because I don't think that users would expect CPU sampling to be enabled when they set `method-sampling-enabled`. This hopefully solves your issue.

As pointed out by @apangin, the `HandleMark` can not be used in the signal handler. I therefore use `NoHandleMark` and added a parameter to vframestream to be able to disable walking continuations in the CPU time sampler.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20752#discussion_r1836559860