RFR: 8309688: Data race on java.io.ClassCache$CacheRef.strongReferent [v5]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'master' into JDK8309688
 - Removed volatile and comment about the benign race
 - Switch to using volatile instead of AtomicReference
 - Merge branch 'master' into JDK8309688
 - 8309688: Data race on java.io.ClassCache.strongReferent

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/14386/files
  - new: https://git.openjdk.org/jdk/pull/14386/files/e9b2e0f2..6da51c22

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14386&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14386&range=03-04

  Stats: 7016 lines in 163 files changed: 465 ins; 6313 del; 238 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