RFR: 8231627: ThreadsListHandleInErrorHandlingTest.java fails in printing all threads [v2]

[Daniel D.Daugherty]

> A small robustness fix in ThreadsSMRSupport::print_info_on() to reduce the
> likelihood of crashes during error reporting. Uses Threads_lock->try_lock()
> for safety and restricts some reporting to when the Threads_lock has been
> acquired (depends on JDK-8256383). Uses a ThreadsListHandle to make
> the current ThreadsList safe for reporting (depends on JDK-8258284). Also
> detects when the system ThreadsList (_java_thread_list) has changed and
> will warn that some of the reported info may now be stale.
> 
> Two existing tests have been updated to reflect the use of a ThreadsListHandle
> in ThreadsSMRSupport::print_info_on(). Mach5 Tier[1-6] testing has no regressions.

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

  Address comments from coleenp and pchilano.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1891/files
  - new: https://git.openjdk.java.net/jdk/pull/1891/files/334bdd2a..c9f4c4e0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1891&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1891&range=00-01

  Stats: 55 lines in 3 files changed: 7 ins; 18 del; 30 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1891.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1891/head:pull/1891

PR: https://git.openjdk.java.net/jdk/pull/1891