RFR: 8279016: JFR Leak Profiler is broken with Shenandoah [v4]

[Aleksey Shipilev]

On Tue, 30 Jul 2024 11:13:22 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> All right, I think I misunderstood how sampling works. I assumed it happens from the GC cycle, but now I see it happens from the allocation path. Indeed sampler holds the object in weak oop storage, and they are supposed to be accessible immediately after the allocation. 
>> 
>> I tightened up comments to reflect this understanding. Looks better, or?
>
> I don't know. The backoff mechanism now introduced is to handle the special case where the LeakProfiler dump operation, even though it is performed under an exclusive safepoint, happens to to coincide with some phase of Shenandoah GC - a lot of surface for handling this special case.
> 
> Also, need this not be categorical for all OldObject tests?

Yes. I think we go for a more comprehensive fix: https://github.com/openjdk/jdk/pull/20328#issuecomment-2434920739

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PR Review Comment: https://git.openjdk.org/jdk/pull/20328#discussion_r1814734821