RFR: 8274349: ForkJoinPool.commonPool() does not work with 1 CPU [v3]

[David Holmes]

> A regression introduced in Java 17 will give the default FJ pool a parallelism of zero in a uniprocessor environment. The fix restores this to a value of 1. See bug report for details.
> 
> Testing:
>  - new regression test
>  - tiers 1-3
> 
> Thanks,
> David

David Holmes has updated the pull request incrementally with one additional commit since the last revision:

  Improved test logic per @martin's comments

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5784/files
  - new: https://git.openjdk.java.net/jdk/pull/5784/files/666f36f4..1344903a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5784&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5784&range=01-02

  Stats: 5 lines in 1 file changed: 1 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5784.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5784/head:pull/5784

PR: https://git.openjdk.java.net/jdk/pull/5784