RFR: 8299414: JVMTI FollowReferences should support references from VirtualThread stack [v9]

[Serguei Spitsyn]

On Mon, 1 May 2023 18:26:30 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

>> The fix updates JVMTI FollowReferences implementation to report references from virtual threads:
>> - unmounted vthreads are detected, their stack references for JVMTI_HEAP_REFERENCE_STACK_LOCAL/JVMTI_HEAP_REFERENCE_JNI_LOCAL;
>> - stacks of mounted vthreads are splitted into 2 parts (virtual thread stack and carrier thread stack), references are reported with correct thread id/class tag/object tags/frame depth;
>> - common code to handle stack frames are moved into separate class;
>> 
>> Threads are reported as:
>> - platform threads: JVMTI_HEAP_REFERENCE_THREAD (as before);
>> - mounted vthreads (synthetic references, consider them as heap roots because carrier threads are roots): JVMTI_HEAP_REFERENCE_OTHER;
>> - unmounted vthreads: not reported as heap roots.
>
> Alex Menkov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Added "no continuations" test case

test/hotspot/jtreg/serviceability/jvmti/vthread/FollowReferences/VThreadStackRefTest.java line 208:

> 206: 
> 207:     private static void verifyVthreadMounted(Thread t, boolean expectedMounted) {
> 208:         // Hucky, but simple.

Nit: Hucky => Hacky ?

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PR Review Comment: https://git.openjdk.org/jdk/pull/13254#discussion_r1182325468