RFR: 8322732: ForkJoinPool may underutilize cores in async mode [v16]

[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 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 50 additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8322732
 - diagnostic
 - Reinstate quiescence signals
 - reshadow; avoid test loop bleed
 - Don't shadow parks
 - re-enable rescan; slim down test
 - unguard signal
 - Merge branch 'openjdk:master' into JDK-8322732
 - Address review comments
 - Merge branch 'openjdk:master' into JDK-8322732
 - ... and 40 more: https://git.openjdk.org/jdk/compare/1dba1675...3836207b

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19131/files
  - new: https://git.openjdk.org/jdk/pull/19131/files/becabd04..3836207b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19131&range=15
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19131&range=14-15

  Stats: 5398 lines in 158 files changed: 3327 ins; 1425 del; 646 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