RFR: 8361912: ThreadsListHandle::cv_internal_thread_to_JavaThread does not deal with a virtual thread's carrier thread [v2]

[Alex Menkov]

On Tue, 22 Jul 2025 05:47:37 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> The `cv_internal_thread_to_JavaThread` method will now check if the thread is a mounted virtual thread, and if so protect the carrier thread. User's of the API that need to deal with virtual threads must still check the carrier themselves as it could change asynchronously, but it is now guaranteed that the carrier JavaThread returned via this method cannot terminate whilst being used (the same as regular platform JavaThreads).
>> 
>> It was noticed whilst updating the documentation that the `JvmtiExport` variant `cv_oop_to_JavaThread` is unused and so can be removed.
>> 
>> Testing:
>> - tiers 1-4
>> 
>> Thanks
>
> David Holmes has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Move comment

I still think that it would be safer to explicitly specify that caller knows that jthread can be virtual thread (and maybe add assert when a caller works only with platform threads, but passed jthread is virtual), but ok, it's up to you.
Currently all callers except `ThreadSnapshotFactory::get_thread_snapshot` use `cv_internal_thread_to_JavaThread` for platform threads only. Do you want to update `ThreadSnapshotFactory::get_thread_snapshot` to utilize new functionality or prefer to do it by separate CR?

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PR Comment: https://git.openjdk.org/jdk/pull/26287#issuecomment-3104940720