RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v50]

[Johannes Bechberger]

On Wed, 4 Jun 2025 17:04:15 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> You're right.
>
> The Threads_lock is required to prevent JFR from sampling through an ongoing safepoint, touching oops, which is not supported by most GCs as well as JFR evolving its global epoch (happens during safepoint) while both threads are outside the safepoint protocol. Can be optimized (later), see for example: https://github.com/openjdk/jdk/pull/25602

I readded the lock.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2127082776