RFR: 8308000: add PopFrame support for virtual threads [v8]

[Alan Bateman]

On Sat, 20 May 2023 00:30:17 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> This enhancement adds `PopFrame` support for virtual threads. The spec defines minimal support that the JVMTI `PopFrame` can be used for a virtual thread suspended an an event. 
>> Actually, the `PopFrame` can supports suspended and mounted virtual threads. 
>> 
>> CSR (approved): https://bugs.openjdk.org/browse/JDK-8308001: add PopFrame support for virtual threads
>> 
>> Testing:
>> New test was developed: `serviceability/vthread/PopFrameTest`.
>> Submitted mach5 tiers 1-6 are good.
>> TBD: rerun mach5 tiers 1-6 at the end of review again if necessary.
>
> Serguei Spitsyn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   PopFrameTest improvements

Spec + impl changes looks okay. I did not review the test changes in detail.

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Marked as reviewed by alanb (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14002#pullrequestreview-1435418671