RFR: JDK-8319662 ForkJoinPool trims worker threads too slowly [v8]

[Doug Lea]

> This update cascades timeouts to trim subsequent workers after the first  keepAlive inactive period.

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 10 additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8319662
 - Remove unnecessary re-interrupt
 - Merge branch 'openjdk:master' into JDK-8319662
 - Reduce oversignalling and contention; add test
 - Revert 2 lines in method scan
 - Merge branch 'openjdk:master' into JDK-8319662
 - Split up method awaitWork; other associated changes.
 - Merge branch 'openjdk:master' into JDK-8319662
 - tweak cascades; reinstate an @Contended; resolve JDK-8319498
 - Support cascading idle timeouts

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/16725/files
  - new: https://git.openjdk.org/jdk/pull/16725/files/6f4b9bb3..980930c0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16725&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16725&range=06-07

  Stats: 33384 lines in 815 files changed: 15447 ins; 14251 del; 3686 mod
  Patch: https://git.openjdk.org/jdk/pull/16725.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16725/head:pull/16725

PR: https://git.openjdk.org/jdk/pull/16725