RFR: 8258284: clean up issues with nested ThreadsListHandles [v2]

[Daniel D.Daugherty]

> While working on JDK-8231627, I discovered there were issues with nested
> ThreadsListHandles. I added a new test to verify how ThreadsListHandles and
> nested ThreadsListHandles are supposed to work. I found two bugs:
> 
> 1) A failure to restore the expected _threads_hazard_ptr when a nested
>     ThreadsListHandle is destroyed.
> 
> 2) A failure to decrement _nested_threads_hazard_ptr_cnt when a nested
>     ThreadsListHandle is destroyed.
> 
> The second failure mode is what tripped up my fix for JDK-8231627 so that
> bug fix depends on this bug fix.
> 
> Mach5 Tier[1-3] testing has no regressions (macOSX testing is incomplete at the moment).

Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:

  Resolve @fisk CR about using Atomic::store().

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1844/files
  - new: https://git.openjdk.java.net/jdk/pull/1844/files/4f1594df..95d77ca1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1844&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1844&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1844.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1844/head:pull/1844

PR: https://git.openjdk.java.net/jdk/pull/1844