RFR: 8286294 : ForkJoinPool.commonPool().close() spins [v2]

[Doug Lea]

> Changes ForkJoinPool.close spec and code to trap close as a no-op if called on common pool

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

  Fix doc types

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8577/files
  - new: https://git.openjdk.java.net/jdk/pull/8577/files/57a7c386..5ceb0794

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8577&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8577&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8577.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8577/head:pull/8577

PR: https://git.openjdk.java.net/jdk/pull/8577