On Wed, 18 Feb 2026 19:19:23 GMT, Serguei Spitsyn <[email protected]> wrote:
>> The `interp-only` mechanism is based on the `JavaThread` objects. Carrier
>> and virtual threads can temporary share the same `JavaThread`. The
>> `java_thread->jvmti_thread_state()` is re-linked to a virtual thread at
>> `mount` and to the carrier thread at `unmount`. The `JvmtiThreadState` has a
>> back link to the `JavaThread` which is also set for virtual thread at a
>> `mount` and carrier thread at an `unmount`. Just one of these two links at
>> the same time is set to the `JavaThread`, the other one has to be set to
>> `nullptr`. The `interp-only` mechanism needs this invariant.
>> However, there is a corner case when this invariant is broken. It happens
>> when the `JvmtiThreadState` for carrier thread has just been created. In
>> such case, the link to `JavaThread` is always `non-nullptr` even though a
>> virtual thread is currently mounted on a carrier thread. This simple update
>> fixes the issue in the `JvmtiThreadState` ctor.
>>
>> Also, this update the includes the `interp_only` implementation
>> simplifications and more asserts are added to relevant places. One of the
>> simplification is a removal of the field `JvmtiThreadState::_thread_saved`.
>>
>> Testing:
>> - TBD: Mach5 tiers 1-6
>
> Serguei Spitsyn has updated the pull request incrementally with one
> additional commit since the last revision:
>
> review: moved comment clarifying _thread from its init to definition
Overall fix looks good, small clean-up related comment only
src/hotspot/share/prims/jvmtiThreadState.cpp line 483:
> 481: invalidate_cur_stack_depth();
> 482: } else {
> 483: assert(!is_enabled(JVMTI_EVENT_FRAME_POP), "Must have no framepops
> set");
This change is not related to the the bug, better to fix separately.
-------------
Changes requested by lmesnik (Reviewer).
PR Review: https://git.openjdk.org/jdk/pull/29436#pullrequestreview-3835072216
PR Review Comment: https://git.openjdk.org/jdk/pull/29436#discussion_r2835859114
