RFR: 8314515: java/util/concurrent/SynchronousQueue/Fairness.java failed with "Error: fair=false i=8 j=0" [v2]

[Viktor Klang]

> While this might not fix 8314515, it should at least make it more exact.

Viktor Klang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - Cleaning up Fairness.java:s underlying queue implementation access
 - Improving SynchronousQueue Fairness test to only proceed once observing that the previous thread is enqueued as a producer

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Changes: https://git.openjdk.org/jdk/pull/17082/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17082&range=01
  Stats: 35 lines in 1 file changed: 28 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/17082.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17082/head:pull/17082

PR: https://git.openjdk.org/jdk/pull/17082