RFR: 8309688: Data race on java.io.ClassCache$CacheRef.strongReferent [v6]

[Man Cao]

> Hi all,
> 
> Could anyone review this small fix for a data race in java.io.ClassCache$CacheRef? This fix makes the code safer by making the code data-race-free.

Man Cao has updated the pull request incrementally with one additional commit since the last revision:

  Update comment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14386/files
  - new: https://git.openjdk.org/jdk/pull/14386/files/6da51c22..83facfa5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14386&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14386&range=04-05

  Stats: 9 lines in 1 file changed: 5 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14386.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14386/head:pull/14386

PR: https://git.openjdk.org/jdk/pull/14386