RFR: 8252221: Use multiple workers for Parallel GC pre-touching [v4]

[Amit Pawar]

> Please review this change.

Amit Pawar has updated the pull request incrementally with one additional commit since the last revision:

  Updated the code as per the review.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/180/files
  - new: https://git.openjdk.java.net/jdk/pull/180/files/d81c3b92..e6c072cc

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=180&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=180&range=02-03

  Stats: 48 lines in 4 files changed: 19 ins; 21 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/180.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/180/head:pull/180

PR: https://git.openjdk.java.net/jdk/pull/180