[jdk17u-dev] RFR: 8306738: Select num workers for safepoint ParallelCleanupTask [v4]

[Aleksey Shipilev]

> Unclean backport to considerably improve the safepoint cleanup times. The backport is not clean, because the `WorkGang` -> `WorkerThreads` rename is missing. The is also the addition of `Dictionary::does_any_dictionary_needs_resizing` check, because JDK 17 is still have that resize code in JDK 17.
> 
> Additional testing:
>  - [x] Ad-hoc benchmarks
>  - [x] Linux x86_64 fastdebug `tier1 tier2 tier3`
> 
> The experiments (see original PR) show we win big on this:
> ![plot](https://github.com/openjdk/jdk17u-dev/assets/1858943/fd69b925-fa69-4e13-ac8c-e0dd72dd43cd)

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into JDK-8306738-safepoint-cleanup-num-workers
 - Backport 672bade522b4641ffc30b0ac09791e8dcf21e003

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

Changes:
  - all: https://git.openjdk.org/jdk17u-dev/pull/1379/files
  - new: https://git.openjdk.org/jdk17u-dev/pull/1379/files/e22e9e37..ceaf49d0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1379&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1379&range=02-03

  Stats: 8826 lines in 1099 files changed: 5002 ins; 409 del; 3415 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1379.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1379/head:pull/1379

PR: https://git.openjdk.org/jdk17u-dev/pull/1379