RFR: 8252103: Parallel heap inspection for ParallelScavengeHeap [v15]

[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:

  use 1u instead of conversion to size_t for block_index
  
  Co-authored-by: Stefan Johansson <54407259+kstefanj at users.noreply.github.com>

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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/ee920861..6b4600a0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=25&range=14
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=25&range=13-14

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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