RFR: 8241403: JavaThread::get_thread_name() should be ThreadSMR-aware

[Daniel D.Daugherty]

A minor fix to add a new function:

    bool Thread::is_JavaThread_protected(const JavaThread* p)

that returns true when the target JavaThread* is protected and false
otherwise. Update JavaThread::get_thread_name() to create a
ThreadsListHandle and use the new is_JavaThread_protected(). Also
update JvmtiTrace::safe_get_thread_name() to use the new
is_JavaThread_protected().

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Commit messages:
 - 8241403: JavaThread::get_thread_name() should be ThreadSMR-aware

Changes: https://git.openjdk.java.net/jdk/pull/2535/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2535&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8241403
  Stats: 51 lines in 4 files changed: 26 ins; 9 del; 16 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2535.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2535/head:pull/2535

PR: https://git.openjdk.java.net/jdk/pull/2535