RFR(XS) Contended Locking speedup PlatformEvent unpark bucket (8061552)

[Daniel D. Daugherty]

Greetings,

I have the Contended Locking speedup PlatformEvent unpark bucket
ready for review. These are small comment only changes that have
already been reviewed by Karen Kinnear (acorn) and Dave Dice (dice).
It would be good to get one or two more pair of eyes on these
comment additions/updates/synchronizations.

Historial reminder:

     Back in 2012.12 and 2013.01, work on the "bug fix bucket" for the
     Contended Locking project was being done. One of the bug fixes was:

     JDK-8004902 correctness fixes motivated by contended locking work 
(6607129)
     https://bugs.openjdk.java.net/browse/JDK-8004902

     The work on JDK-8004902 picked up all of the code changes and many of
     comments that were part of this bucket (speedup PlatformEvent unpark).

     Here's the webrev for "bug fix bucket":

     http://cr.openjdk.java.net/~dcubed/cl_bug_fix_bucket-webrev/2/

     The bug fix bucket included fixes for 6444286, 8004902 and 8004903,
     but the majority of the work was done for 8004902. Now back to the
     current thread...

This work is being tracked by the following bug ID:

     JDK-8061552 Contended Locking speedup PlatformEvent unpark bucket
     https://bugs.openjdk.java.net/browse/JDK-8061552

Here is the webrev URL:

http://cr.openjdk.java.net/~dcubed/8061552-webrev/2-jdk9-hs-rt/

Here is the JEP link:

     https://bugs.openjdk.java.net/browse/JDK-8046133

Testing:

- JPRT test jobs