RFR: 8352251: Implement Cooperative JFR Sampling [v16]

[Markus Grönlund]

On Mon, 5 May 2025 17:31:37 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

> > Can we let _last_sender_Java_fp be a state field that can be tested?
> 
> I still couldn't hit any failures or errors with my simple version, but I understand that it might be problematic.
> 
> I have an implementation: [TheRealMDoerr at b2f83fa](https://github.com/TheRealMDoerr/jdk/commit/b2f83fae262f129f864e109d7adce169e28f0c7c) Please take a look. I hope we don't need more ;-) I'm planning to run more test when I find more time.
> 
> If `_last_sender_Java_fp` is needed on all platforms, shouldn't it be better moved to shared javaFrameAnchor.hpp and javaThread.hpp?

I removed the strongest assertions from jfrThreadSampling.cpp compute_top_frame() and compute_sender_frame(). Still, I would expect you occasionally to crash hard in the JfrVframeStream iterator during stack walking.

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PR Comment: https://git.openjdk.org/jdk/pull/24296#issuecomment-2851815322