RFR: 8308000: add PopFrame support for virtual threads

[David Holmes]

On Tue, 16 May 2023 23:27:37 GMT, Leonid Mesnik <lmesnik 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.
>
> test/hotspot/jtreg/serviceability/jvmti/vthread/PopFrameTest/PopFrameTest.java line 62:
> 
>> 60:     static final int FAILED = 2;
>> 61: 
>> 62:     static void log(String str) { System.out.println(str); }
> 
> Better to flush system.out after each print.

System.out has autoflush enabled so `println` will trigger a flush.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14002#discussion_r1195822943