RFR: 8256474: Migrate Mutex _owner accesses to use Atomic operations [v3]

[David Holmes]

> Simple update to move away from volatile fields and use Atomic::load/store on racy accesses.
> 
> Thanks,
> David

David Holmes has updated the pull request incrementally with one additional commit since the last revision:

  Restore volatile modifier

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1402/files
  - new: https://git.openjdk.java.net/jdk/pull/1402/files/fa203cb5..0b9351ea

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1402&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1402&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1402.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1402/head:pull/1402

PR: https://git.openjdk.java.net/jdk/pull/1402