RFR: 8310037: Parallel/Serial: Space Counters classes leak helper instances [v2]

[Zhengyu Gu]

> Please review this small fix for memory leak.

Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:

  tschatzl's suggestion

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14472/files
  - new: https://git.openjdk.org/jdk/pull/14472/files/7b4c83d4..988fe8da

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14472&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14472&range=00-01

  Stats: 11 lines in 3 files changed: 6 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/14472.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14472/head:pull/14472

PR: https://git.openjdk.org/jdk/pull/14472