RFR: 8346142: [perf] scalability issue for the specjvm2008::xml.validation workload [v2]

[Vladimir Ivanov]

> The double check needs less time vs enter to 'synchronize' block when it not needed. This patch for the xml.validation workload for runs with 112 threads reports ~2.5% improvement on the server with Xeon 8480:
> orig: 1T - 433.64 ops/m, 112T - 17344.25 ops/m
> patched: 1T - 437.01 ops/m, 112T - 17771.94 ops/m
> 
> The tier1 and jaxp tests are OK with this patch.

Vladimir Ivanov has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8346142
 - 8346142 [perf] scalability issue for the specjvm2008::xml.validation workload

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22723/files
  - new: https://git.openjdk.org/jdk/pull/22723/files/0e73a89a..20554293

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22723&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22723&range=00-01

  Stats: 530558 lines in 8910 files changed: 288054 ins; 192740 del; 49764 mod
  Patch: https://git.openjdk.org/jdk/pull/22723.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22723/head:pull/22723

PR: https://git.openjdk.org/jdk/pull/22723