[jdk21u-dev] RFR: 8324933: ConcurrentHashTable::statistics_calculate synchronization is expensive

[Aleksey Shipilev]

Backporting this simple performance improvement for, well, performance. Also 21.0.4-oracle parity.

Additional testing:
 - [ ] Linux x86_64 server fastdebug, `all`

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Commit messages:
 - Backport 0e2fdc95ae47c11e6a1e47cdc6190268e29a9d9c

Changes: https://git.openjdk.org/jdk21u-dev/pull/524/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=524&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324933
  Stats: 20 lines in 1 file changed: 8 ins; 1 del; 11 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/524.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/524/head:pull/524

PR: https://git.openjdk.org/jdk21u-dev/pull/524