> See the bug for more discussion and reproducer. This PR replaces the ad-hoc 
> linked list with the `ArrayList` wrapper that manages synchronization, search 
> and replacements efficiently. Arrays are easy targets for GC. There are 
> possible improvements here, most glaring is parallelism that is currently 
> knee-capped by global synchronization. The synchronization scheme follows 
> what we have in original code, and I think it is safer to continue with it 
> right now.
> 
> I'll put performance data in a separate comment.
> 
> Additional testing:
>  - [x] Original reproducer improves drastically
>  - [x] New microbenchmark shows no regression on "churning" tests, which 
> covers insertion/removal perf
>  - [x] New microbenchmark shows improvement on Full GC times (crude, but 
> repeatable), serves as a proxy for reproducer
>  - [x] `java/lang/ref` tests in release 
>  - [x] `all` tests in fastdebug

Aleksey Shipilev has updated the pull request incrementally with one additional 
commit since the last revision:

  Review feedback: make sure trimming actually works, stylistic changes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22043/files
  - new: https://git.openjdk.org/jdk/pull/22043/files/0194c9bc..d4a03d85

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22043&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22043&range=03-04

  Stats: 40 lines in 2 files changed: 18 ins; 0 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/22043.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22043/head:pull/22043

PR: https://git.openjdk.org/jdk/pull/22043

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