RFR: 8296401: ConcurrentHashTable::bulk_delete might miss to delete some objects [v4]

[Leo Korinth]

> ConcurrentHashTable::bulk_delete might miss to delete some objects if a bucket has more than 256 entries. Current uses of ConcurrentHashTable are not harmed by this behaviour. 
> 
> I modified gtest:ConcurrentHashTable to detect the problem (first commit), and fixed the problem in the code (second commit).
> 
> Tests passes tier1-3.

Leo Korinth has updated the pull request incrementally with two additional commits since the last revision:

 - renam stack limit, and add comments
 - Make ndel a reference to a pointer so that we can poison it. Also fix
   POISON_PTR to be of correct type (the pointer is const, not the memory
   pointed to).

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/10983/files
  - new: https://git.openjdk.org/jdk/pull/10983/files/1292acbf..da74384f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10983&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10983&range=02-03

  Stats: 20 lines in 2 files changed: 9 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/10983.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10983/head:pull/10983

PR: https://git.openjdk.org/jdk/pull/10983