[jdk21u-dev] RFR: 8319048: Monitor deflation unlink phase prolongs time to safepoint

[Aleksey Shipilev]

Clean backport to improve TTSP under heavy monitor deflation, and provide better parity.

Additional testing:
 - [x] Ad-hoc benchmarks show TTSP improvements
 - [x] MacOS AArch64 server fastdebug, `runtime/Monitor` passes
 - [ ] Linux AArch64 server fastdebug, `all`

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Commit messages:
 - Backport efc392259c64986bbbe880259e95b09058b9076a

Changes: https://git.openjdk.org/jdk21u-dev/pull/369/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=369&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319048
  Stats: 235 lines in 4 files changed: 221 ins; 0 del; 14 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/369.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/369/head:pull/369

PR: https://git.openjdk.org/jdk21u-dev/pull/369