RFR: 8364258: ThreadGroup constant pool serialization is not normalized [v2]

[Markus Grönlund]

> 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:

  const Handle

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/26558/files
  - new: https://git.openjdk.org/jdk/pull/26558/files/cec818ab..8c025caf

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26558&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26558&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/26558.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26558/head:pull/26558

PR: https://git.openjdk.org/jdk/pull/26558