RFR: 8252103: Parallel heap inspection for ParallelScavengeHeap [v6]

[Lin Zang]

> - Parallel heap iteration support for PSS
> - JBS:  https://bugs.openjdk.java.net/browse/JDK-8252103

Lin Zang has updated the pull request incrementally with one additional commit since the last revision:

  fix constant coding style and do code refine

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/25/files
  - new: https://git.openjdk.java.net/jdk/pull/25/files/d1ca71d8..2d432f95

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=25&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=25&range=04-05

  Stats: 8 lines in 3 files changed: 0 ins; 2 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/25.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/25/head:pull/25

PR: https://git.openjdk.java.net/jdk/pull/25