[jdk17u-dev] RFR: 8305670: Performance regression in LockSupport.unpark with lots of idle threads

[Goetz Lindenmaier]

I backport this for parity with 17.0.9-oracle.

I had to resolve one chunk due to NULL/nullptr differences.

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Commit messages:
 - Backport f030937a51b95dde33ce33537ee830153b2c3b56

Changes: https://git.openjdk.org/jdk17u-dev/pull/1604/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1604&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305670
  Stats: 52 lines in 3 files changed: 39 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1604.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1604/head:pull/1604

PR: https://git.openjdk.org/jdk17u-dev/pull/1604