RFR: 8280554: resourcehogs/serviceability/sa/ClhsdbRegionDetailsScanOopsForG1.java can fail if GC is triggered [v2]

[Chris Plummer]

> When using -Xcomp, the liveness of some objects the test allocates is more precisely known, allowing the objects to be collected before the test expects. This became an issue in the loom repo because it has changes that result in a full GC when the codecache is swept. This is fixed by using statics to reference the objects. Also, if a GC does happen, this seems to get rid of the Survivor region, so the test was updated to no longer check for it.
> 
> I'm choosing to fix this in the jdk repo rather than the loom repo since it is a latent bug that theoretically could occur even without the loom changes, and also to help reduce the amount of changes to be reviewed when loom is integrated into jdk.

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

  Use Reference.reachabilityFence() instead of static field.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7257/files
  - new: https://git.openjdk.java.net/jdk/pull/7257/files/99235d74..c69d7411

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7257&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7257&range=00-01

  Stats: 7 lines in 1 file changed: 4 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7257.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7257/head:pull/7257

PR: https://git.openjdk.java.net/jdk/pull/7257