RFR: 8267842: SIGSEGV in get_current_contended_monitor [v3]

[Martin Doerr]

> We need a fix for crashes in get_current_contended_monitor due to concurrent modification of memory locations which are not declared volatile. See bug for details.

Martin Doerr has updated the pull request incrementally with one additional commit since the last revision:

  New solution: Use Atomic::load/store in current_pending/waiting_monitor accessors.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4224/files
  - new: https://git.openjdk.java.net/jdk/pull/4224/files/97a7df60..f4005ec0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4224&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4224&range=01-02

  Stats: 14 lines in 2 files changed: 3 ins; 5 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4224.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4224/head:pull/4224

PR: https://git.openjdk.java.net/jdk/pull/4224