RFR: 8292591: Experimentally add back barrier-less Java thread transitions

Thu Sep 1 17:07:08 UTC 2022

Please consider, only implemented on x64/aarch64 linux/windows.

On my box calling clock_gettime via JNI goes from 35ns to 28ns when enabled.

Passes t1-7 with option forced on, also passes t1-4 as is in this PR.

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Commit messages:
 - 8292591 - initial

Changes: https://git.openjdk.org/jdk/pull/10123/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10123&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292591
  Stats: 381 lines in 19 files changed: 355 ins; 0 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/10123.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10123/head:pull/10123

PR: https://git.openjdk.org/jdk/pull/10123