RFR: 8275415: Prepare Leak Profiler for Lilliput

[Markus Grönlund]

Greetings,

Currently, the associated chain for a leak candidate (represented by the leak context edge) is stored as a pointer in the mark word. With Lilliput, this will not work.

Providing another hashtable works fine to solve this problem, but the overhead might not fully warrant it. The default hashtable has 1009 buckets IIRC, but the number of leak candidates (samples) found during heap traversal might only be a relatively small number (default queue size is 256).

A solution is to still use space available in the mark word, since we have already provisioned to use this as a "scratch area" as part of setup. It is now limited to accommodate the anticipated changes under the Lilliput project (i.e. restricted to use only the lower 32-bits only) and instead of storing a pointer to the leak context edge, we store an index into an array. 

Testing: jdk_jfr

Thanks
Markus

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Commit messages:
 - Prepare Leak Profiler for Lilliput

Changes: https://git.openjdk.java.net/jdk/pull/5992/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5992&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275415
  Stats: 105 lines in 3 files changed: 75 ins; 23 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5992.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5992/head:pull/5992

PR: https://git.openjdk.java.net/jdk/pull/5992