RFR: 8360046: Scalability issue when submitting virtual threads with almost empty tasks [v9]

[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:

  Revert Exchanger for separate PR

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26479/files
  - new: https://git.openjdk.org/jdk/pull/26479/files/31d2f486..b6b1356e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26479&range=07-08

  Stats: 50 lines in 1 file changed: 13 ins; 3 del; 34 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