RFR: 8364258: ThreadGroup constant pool serialization is not normalized [v8]

[Erik Gahlin]

On Fri, 1 Aug 2025 17:45:29 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> Greetings,
>> 
>> The following change set normalizes the ThreadGroup constants being serialized to the .jfr binary file.
>> 
>> It does this in two parts:
>> 
>> 1. Re-inserts a scavenging scheme to remove stale (unloaded) ThreadGroups; some logic that we used to have in place, but may have been lost as part of the major refactoring around JFR Event Streaming, or even earlier.
>> 2. Introduces a per-epoch "is_serialized" scheme, building on top of JFR epoch generations.
>> 
>> Problem manifestation is a very high number of duplicated TGs (jdk.types.ThreadGroup) as part of JFR checkpoints.
>> 
>> Testing: jdk_jfr
>> 
>> Thanks
>> Markus
>
> Markus Grönlund has updated the pull request incrementally with one additional commit since the last revision:
> 
>   do not attempt to serialize a null thread group

Marked as reviewed by egahlin (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/26558#pullrequestreview-3080950856