The changes for 6984287 broke parallel reference porocessing with the CMS collector.
The fix for 6668573 provided a temporary fix for it in hs21 (JDK 7), but hs20 (6u25)
is still broken.
I am filing this CR, just so that someone searching bugster for the problem
is able to find it and as necessary is able to backport the necessary
fixes, or make use of the temporary fixes to provide a cleaner fix
in the future.
For the purposes of tracking and for process reasons, I will create a subCR for hs20 and
close this, the JDK 7/hs21 CR as a duplicate of 6668573 since it contains
a fix for that problem.
To reproduce the problem run with the flags: -XX:+UseConcMarkSweepGC -XX:+ParallelRefProcEnabled.
The JVM will either hang or crash during the first stage of parallel reference processing,
usually when attempting to terminate a parallel work phase.