RFR: 8360046: Scalability issue when submitting virtual threads with almost empty tasks [v19]

[Doug Lea]

> This set of updates reduces contention-based performance loss under heavy over-subscription, while also improving perfomance more generally.

Doug Lea 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 29 additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8360046
 - Signal on setParallelism
 - Drop added Contended region; simplify accordingly
 - Tweaks
 - Merge branch 'openjdk:master' into JDK-8360046
 - Seperate repolling policies
 - Faster quiescent termination
 - Fix push, refactor deactivate
 - Use absolute timed waits
 - Reduce deactivate/reactivate and cancelled timeout rates
 - ... and 19 more: https://git.openjdk.org/jdk/compare/04687de2...383f9238

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26479/files
  - new: https://git.openjdk.org/jdk/pull/26479/files/891eff05..383f9238

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=18
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=17-18

  Stats: 80875 lines in 1160 files changed: 54702 ins; 18645 del; 7528 mod
  Patch: https://git.openjdk.org/jdk/pull/26479.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26479/head:pull/26479

PR: https://git.openjdk.org/jdk/pull/26479