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

[Daniel D. Daugherty]

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

Thumbs up on the changes. I think I only have a few nits.

src/hotspot/share/prims/jvmtiExport.cpp line 871:

> 869: //
> 870: jvmtiError
> 871: JvmtiExport::cv_oop_to_JavaThread(ThreadsList * t_list, oop thread_oop,

When did `JvmtiExport::cv_oop_to_JavaThread` become unused?

src/hotspot/share/runtime/threadSMR.cpp line 833:

> 831:       return false;
> 832:     } else {
> 833:       // For virtual thread's we need to extract the carrier's JavaThread - if any.

nit typo: s/thread's/threads/

src/hotspot/share/runtime/threadSMR.hpp line 72:

> 70: //   :  // do stuff with 'jt'...
> 71: //
> 72: // A JavaThread* that is included in the ThreadsList that is held by

Why change just this location from `JavaThread *` to `JavaThread*`?
There are other places that you touched that still use `JavaThread *`.

src/hotspot/share/runtime/threadSMR.hpp line 310:

> 308:   inline Iterator end();
> 309: 
> 310:   bool cv_internal_thread_to_JavaThread(jobject jthread, JavaThread** jt_pp, oop* thread_oop_p);

I wish I could remember why in the world I put a space before the `*` when I
did this code so very long ago...

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Marked as reviewed by dcubed (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26287#pullrequestreview-3056275005
PR Review Comment: https://git.openjdk.org/jdk/pull/26287#discussion_r2231715585
PR Review Comment: https://git.openjdk.org/jdk/pull/26287#discussion_r2231668135
PR Review Comment: https://git.openjdk.org/jdk/pull/26287#discussion_r2231710443
PR Review Comment: https://git.openjdk.org/jdk/pull/26287#discussion_r2231713403