RFR: 8360046: Scalability issue when submitting virtual threads with almost empty tasks [v4]

[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 11 additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8360046
 - Undo inadvertent acquire change
 - Add adapt(callable) case to test
 - Whitespace
 - Merge branch 'openjdk:master' into JDK-8360046
 - Avoid unnecessary use of InterruptibleTask; misc cleanup
 - revert runWorker; tweak external probes
 - reduce contention
 - Merge branch 'openjdk:master' into JDK-8360046
 - For testing
 - ... and 1 more: https://git.openjdk.org/jdk/compare/4c894902...c16c1282

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26479/files
  - new: https://git.openjdk.org/jdk/pull/26479/files/6b22e247..c16c1282

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=02-03

  Stats: 1514 lines in 102 files changed: 745 ins; 510 del; 259 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