RFR: 8322732: ForkJoinPool may underutilize cores in async mode [v6]

[Doug Lea]

> This set of changes address causes of poor utilization with small numbers of cores due to overly aggressive contention avoidance. A number of further adjustments were needed to still avoid most contention effects in deployments with large numbers of cores

Doug Lea has updated the pull request incrementally with two additional commits since the last revision:

 - Add test for utilization with interdependent tasks
 - Un-misplace onSpinWait call

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19131/files
  - new: https://git.openjdk.org/jdk/pull/19131/files/72224779..a262f6c6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19131&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19131&range=04-05

  Stats: 52 lines in 2 files changed: 51 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19131.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19131/head:pull/19131

PR: https://git.openjdk.org/jdk/pull/19131