RFR: 8334394: Race condition in Class::protectionDomain [v3]

[Weijun Wang]

> Make sure `pd` is always the same object when `getProtectionDomain0` is null.

Weijun Wang has updated the pull request incrementally with two additional commits since the last revision:

 - var to real type
 - rename

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19752/files
  - new: https://git.openjdk.org/jdk/pull/19752/files/4ce5bc24..ed2ba88a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19752&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19752&range=01-02

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/19752.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19752/head:pull/19752

PR: https://git.openjdk.org/jdk/pull/19752