RFR: 8338383: Implement JEP 491: Synchronize Virtual Threads without Pinning [v30]

[Alan Bateman]

On Tue, 5 Nov 2024 07:48:40 GMT, Erik Gahlin <egahlin at openjdk.org> wrote:

>> Patricio Chilano Mateo has updated the pull request incrementally with five additional commits since the last revision:
>> 
>>  - Add oopDesc::has_klass_gap() check
>>  - Rename waitTimeout/set_waitTimeout accessors
>>  - Revert suggestion to ThawBase::new_stack_frame
>>  - Improve JFR pinned reason in event
>>  - Use freeze_result consistently
>
> src/hotspot/share/jfr/metadata/metadata.xml line 160:
> 
>> 158: 
>> 159:   <Event name="VirtualThreadPinned" category="Java Virtual Machine, Runtime" label="Virtual Thread Pinned" thread="true" stackTrace="true">
>> 160:     <Field type="string" name="blockingOperation" label="Blocking operation" />
> 
> Previously, the event was in the "Java Application" category. I think that was a better fit because it meant it was visualized in the same lane in a thread graph. See here for more information about the category:
> 
> https://docs.oracle.com/en/java/javase/21/docs/api/jdk.jfr/jdk/jfr/Category.html
> 
> (Note: The fact that the event is now written in the JVM doesn't determine the category.)

Thanks for spotting this, it wasn't intended to change the category. I think it's that Event element was copied from another event when adding it to metadata.xml and value that was in the `@Catalog` wasn't carried over.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21565#discussion_r1828915229