RFR: 8233697: CHT: Iteration parallelization

[Ivan Walulya]

Hi,

Please review this change to add parallel iteration of the ConcurrentHashTable. The iteration should be done during a safepoint without concurrent modifications to the ConcurrentHashTable.

Usecase is in parallelizing the merging of large remsets for G1.

Testing: tier 1-3

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

Commit messages:
 - 8233697: CHT: Iteration parallelization

Changes: https://git.openjdk.org/jdk/pull/10759/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10759&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8233697
  Stats: 200 lines in 3 files changed: 200 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10759.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10759/head:pull/10759

PR: https://git.openjdk.org/jdk/pull/10759