RFR: 8352251: Implement JEP 518: JFR Cooperative Sampling [v34]

[Martin Doerr]

On Thu, 22 May 2025 10:24:42 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> The crit sec to be stored before the poll test is issued.
>> 
>> Most likely not needed, because of implicit fences involved in thread suspension.
>
>> The crit sec to be stored before the poll test is issued.
>> 
>> Most likely not needed, because of implicit fences involved in thread suspension.
> 
> OK, but reading `sampling_critical_section` doesn't seem to have any synchronization at all, so it doesn't much matter what you do when writing it.

@theRealAph: src/hotspot/cpu/aarch64/javaFrameAnchor_aarch64.hpp contains 3 release barriers. I wonder if there are cases in which we need ordering which is not already covered by signal handler or suspend/resume mechanism.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24296#discussion_r2102771974