RFR: JDK-8319662 ForkJoinPool trims worker threads too slowly [v2]

[Doug Lea]

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

Doug Lea has updated the pull request incrementally with one additional commit since the last revision:

  tweak cascades; reinstate an @Contended; resolve JDK-8319498

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16725/files
  - new: https://git.openjdk.org/jdk/pull/16725/files/bd5df5ea..a3c96c6a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16725&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16725&range=00-01

  Stats: 56 lines in 1 file changed: 20 ins; 5 del; 31 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