On Tue, 19 Dec 2023 21:34:10 GMT, Alex Menkov <amen...@openjdk.org> wrote:
> I mean race between virtual thread state change and the thread stack switch > (to/from carrier). I'm not sure if I understand you correctly or if we can call it a race. Alan will correct me if I'm wrong. You are talking about thread state change. At least, mount state transition happens on the same JavaThread (it seems, you call it thread state switch). Mount state transition can go over a safepoint. But it should not progress while in a safepoint. David pointed out, "this was all happening at a global safepoint". My understanding is this assumption is correct. Then your approach `to identify that a virtual thread is mounted or not` should work in general. The condition `java_lang_VirtualThread::carrier_thread(vt) != nullptr` should indicate that the `vt` is mounted or is being in mount or unmount transition. If the `vt` is in mount or unmount transition then (it is a gray zone) the way we identify mounted state should match the way we did it when dumped mounted virtual threads. It is done this way: `oop mounted_vt = thread->is_vthread_mounted() ? thread->vthread() : nullptr;` So, it seems any of yous suggestion should work here. Though, it would be nice to simplify it a little if possible. Again, to be consistent, a `vt` in mount state transition just have to be identified as mounted or unmounted in both fragments in a similar way . ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/17134#discussion_r1434006417
