On Thu, 31 Aug 2023 10:38:32 GMT, Markus Grönlund <[email protected]> wrote:
>> In the virtual thread implementation, thread identity switches to the
>> carrier before freezing and switches back to the virtual thread after
>> thawing. This was a forced move due to issues getting JVMTI to work with
>> virtual threads. JVMTI can now hide events during transitions so we can
>> invert the sequence back to mounting before running the continuation,
>> unmounting after freezing, and re-mounting after thawing. This sequence is
>> important for future changes that will initiate the freezing from the VM.
>>
>> The change requires an update to the JFR thread sampler to skip sampling
>> when it samples during a transition.
>>
>> Testing: tier1-5
>
> src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp line 410:
>
>> 408: }
>> 409: if (JAVA_SAMPLE == type) {
>> 410: if (thread_state_in_java(thread) &&
>> !is_vthread_in_transition(thread)) {
>
> I think this check can be postponed until after the thread is suspended.
Is the check in OSThreadSampler::protected_task in the right place? That seems
to be a suspended context.
For JfrThreadSampleClosure::do_sample_thread, I think I may have mis-read the
code. I thought it was suspended but looking at it again them maybe it should
be the JfrNativeSamplerCallback implementation. This is probably an area where
I need help to get right.
Is JfrNativeSamplerCallback
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PR Review Comment: https://git.openjdk.org/jdk/pull/15492#discussion_r1311502783
