RFR: 8011218 Kitchensink hanged, likely NMT is to blame

[Zhengyu Gu]

The thread that runs NMT query can be blocked on NMT snapshot lock, 
which prevents JVM to reach safepoints.

NMT query does not change Java heap, it does not have to stop for 
safepoints. So the solution is to transition to _vm_in_native state, 
before executing NMT query.


JBS: https://jbs.oracle.com/bugs/browse/JDK-8011218
Public bug: not available
Webrev: http://cr.openjdk.java.net/~zgu/8011218/webrev.00/ 
<http://cr.openjdk.java.net/%7Ezgu/8011218/webrev.00/>


Test:
   - Run Kitchensink stress test on low power machine Linux x86 machine 
with GC trace on, stress out NMT query thread by submitting NMT query in 
a loop, NMT query executions become very slow, but GC trace continues 
generating message, and does not show long pause.

Thanks,

-Zhengyu