RFR: 8267842: SIGSEGV in get_current_contended_monitor [v2]

[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:

  Add comments as suggested by Dan.

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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/6e444fab..97a7df60

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4224&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4224&range=00-01

  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 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