RFR: 8299426: Heap dump does not contain virtual Thread stack references [v2]

[Chris Plummer]

On Wed, 29 Nov 2023 22:22:09 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

> There is a check for virtual thread liveness which has to be good enough in general:
> 
> ```
> 1617   static bool should_dump_vthread(oop vt) {
> 1618     return java_lang_VirtualThread::state(vt) != java_lang_VirtualThread::NEW
> 1619         && java_lang_VirtualThread::state(vt) != java_lang_VirtualThread::TERMINATED;
> 1620   }
> . . .
> 1919     if (java_lang_VirtualThread::is_instance(o) && ThreadDumper::should_dump_vthread(o)) {
> 1920       _vthread_dumper->dump_vthread(o, writer());
> 1921     }
> ```

That should in general take care of most unreachable virtual threads, but technically I don't think a virtual thread has to reach the TERMINATED state in order to become unreachable. However, it will never get scheduled.

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PR Comment: https://git.openjdk.org/jdk/pull/16665#issuecomment-1833132940