RFR: 8360046: Scalability issue when submitting virtual threads with almost empty tasks [v7]

[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 14 additional commits since the last revision:

 - 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
 - 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
 - ... and 4 more: https://git.openjdk.org/jdk/compare/1ec5c22e...51950550

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26479/files
  - new: https://git.openjdk.org/jdk/pull/26479/files/54220a19..51950550

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=05-06

  Stats: 74512 lines in 2216 files changed: 45912 ins; 19576 del; 9024 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