RFR: 8360046: Scalability issue when submitting virtual threads with almost empty tasks [v18]

[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 incrementally with one additional commit since the last revision:

  Drop added Contended region; simplify accordingly

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26479/files
  - new: https://git.openjdk.org/jdk/pull/26479/files/40a624e1..891eff05

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=17
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=16-17

  Stats: 74 lines in 1 file changed: 12 ins; 7 del; 55 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