RFR (S): 8136854: G1 ConcurrentG1RefineThread::stop delays JVM shutdown for >150ms

[Thomas Schatzl]

Hi all,

  can I have reviews for this small fix to decrease startup time of the
G1 collector by increasing the polling frequency of the main thread to
look whether all concurrent mark threads already completed their
initialization.

There are some additional volatile declarations of variables that are
set by multiple threads.

We are aware that this might not be an ideal solution, some kind of
wait/notify scheme for the mark threads might be better. That would be
much more work though. I created JDK-8148359 for this work.

CR:
https://bugs.openjdk.java.net/browse/JDK-8136854
Webrev:
http://cr.openjdk.java.net/~tschatzl/8136854/webrev/
Testing:
jprt, local testing, dev-submit perf testing

Thanks,
  Thomas