RFR: 8360046: Scalability issue when submitting virtual threads with almost empty tasks [v11]

[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 19 additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8360046
 - Reduce park/unpark rates
 - Add @Contended WorkQueue region. Adapt accordingly.
 - Revert Exchanger for separate PR
 - revive topLevelExec, adjust occrdingly; small teaks and copy-edits
 - Merge branch 'openjdk:master' into JDK-8360046
 - Refactor to improve locality and signalling
 - Avoid underutilization on resize
 - Merge branch 'openjdk:master' into JDK-8360046
 - Undo inadvertent acquire change
 - ... and 9 more: https://git.openjdk.org/jdk/compare/eaacff13...2c3565b5

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26479/files
  - new: https://git.openjdk.org/jdk/pull/26479/files/af46e1c7..2c3565b5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=10
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=09-10

  Stats: 179598 lines in 2211 files changed: 141773 ins; 24076 del; 13749 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