RFR(M): 8191798 redo nested ThreadsListHandle to drop Threads_lock

[Daniel D. Daugherty]

Greetings,

We have a fix for the following Thread-SMR bug:

     JDK-8191798 redo nested ThreadsListHandle to drop Threads_lock
     https://bugs.openjdk.java.net/browse/JDK-8191798

Erik O is the primary author for this fix; I've only made minor tweaks
here and there to the comments, the code and the tests. I have the
Thread-SMR stress testing setup on my Solaris-X64 server so I'm the
one shepherding the fix forward.

Summary: Refactor Thread hazard ptrs and nested ThreadsLists into
     SafeThreadsListPtr.

Hazard ptr management logic remains the same, but the nested ThreadsList
management logic uses a linked list of SafeThreadsListPtr and safe counters
instead of a linked list of NestedThreadsList and the Threads_lock.


Webrev URLs:

http://cr.openjdk.java.net/~dcubed/8191798-webrev/1_for_jdk_jdk.full_no_code_motion/
     This is the webrev to look at if you want to see the entire
     proposed fix without code motion noise.

http://cr.openjdk.java.net/~dcubed/8191798-webrev/1_for_jdk_jdk.code_motion_only/
     This webrev is only code motion and is here for completeness.

http://cr.openjdk.java.net/~dcubed/8191798-webrev/1_for_jdk_jdk.full_with_code_motion/
     This webrev is everything and is here for completeness.

Testing:
- Mach5 
builds-tier1,jdk-tier1,jdk-tier2,jdk-tier3,hs-tier1,hs-tier2,hs-tier3
   - multiple rounds - no test failures
- Solaris X64 Thread-SMR stress testing - 2 x 24+ hour runs - no failures
   related to these changes

Thanks, in advance, for any comments, suggestions or questions.

Dan and Erik