[master] RFR: 8264311: Heap object statistics [v4]

[Roman Kennke]

> For Lilliput evaluation, it would be useful to be able to get some statistics about heap objects, e.g. how many objects there typically are, what is their (average) size, how big is the live data set, how many objecs have an identity hash code and how many objects are locked. Some of that information may be useful for general purpose too, e.g. the avg live data set and object size/count information might be quite useful to have.
> 
> Heap object statistics can be gathered and printed by invoking java with -XX:+UnlockDiagnosticVMOptions -XX:+HeapObjectStats -Xlog:heap+stats. It will impact performance of the workload. The sampling interval can be specificed by -XX:HeapObjectStatsSamplingInterval=X (in ms) and defaults to 500 (ms).
> 
> Testing:
>  - [x] Some manual tests, verifying the plausability of the output by hand
>  - [x] tier1
>  - [x] tier2

Roman Kennke has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Remove unused variable/statement
 - Remove unused field
 - 8264311: Heap object statistics

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Changes: https://git.openjdk.java.net/lilliput/pull/1/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lilliput&pr=1&range=03
  Stats: 253 lines in 6 files changed: 252 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/lilliput/pull/1.diff
  Fetch: git fetch https://git.openjdk.java.net/lilliput pull/1/head:pull/1

PR: https://git.openjdk.java.net/lilliput/pull/1