RFR: 8364343: Virtual Thread transition management needs to be independent of JVM TI [v9]

[Coleen Phillimore]

On Wed, 26 Nov 2025 22:47:25 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

>> src/hotspot/share/prims/jvmtiEnvBase.cpp line 1772:
>> 
>>> 1770: 
>>> 1771:   assert(java_thread != nullptr, "sanity check");
>>> 1772:   assert(!java_thread->is_in_VTMS_transition(), "sanity check");
>> 
>> Why don't you need these asserts anymore?
>
> We can’t assert this because it could be temporarily set by the target while trying to transition. Previously we had two fields in JavaThread, `_VTMS_transition_mark` and `_is_in_VTMS_transition`. `_VTMS_transition_mark` was set first (checked by the disabler), and if transitions were disabled we waited. Once the transition could start we set `_is_in_VTMS_transition`. 
> Going over the changes I see I removed one assert in `JvmtiEnvBase::get_vthread_jvf` that should be okay to keep, so I restored it. Also added an assert in `JavaThread::is_in_VTMS_transition()` (now `is_in_vthread_transition`) to verify that if it’s accessed from another thread then it has to be done from a safe context where the value will not change right after checking.

okay.  seems like a better place for it.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28361#discussion_r2578224144