RFR: 8360201: JFR: Initialize JfrThreadLocal::_sampling_critical_section [v2]

[Markus Grönlund]

On Mon, 23 Jun 2025 16:31:45 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Initially found by UBSan. I was not able to reproduce it locally, @MBaesken would try. But the problem seems obvious: the initial value for the `bool` field is garbage. I have checked other fields in `JfrThreadLocal`, they seem fine.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 server fastdebug, `jdk_jfr`
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8360201-jfr-init-threadlocal
>  - Fix

Marked as reviewed by mgronlun (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/25938#pullrequestreview-2951308088