RFR: 8328611: Thread safety issue in com.sun.tools.jdi.ReferenceTypeImpl::classObject [v2]

[Chris Plummer]

> Fixed "double-checked-locking" bug in `ReferenceImplType.classObject()`. Details in the first comment. Tested with the following:
> - com/sun/jdi
> - nsk/jdi
> - nsk/jdwp
> - nsk/jdb

Chris Plummer has updated the pull request incrementally with one additional commit since the last revision:

  Add period at end of comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19439/files
  - new: https://git.openjdk.org/jdk/pull/19439/files/97376705..58295072

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19439&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19439&range=00-01

  Stats: 7 lines in 1 file changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/19439.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19439/head:pull/19439

PR: https://git.openjdk.org/jdk/pull/19439