For quite a while, across different VM testruns rare timeouts in some PCL tests have been observed.
The hang was reproduced with jdk7b79 on linux-i586.
"-server -Xcomp -XX:+UseConcMarkSweepGC" VM options were used.

It's really rare - it takes ~10k runs to get a hang, so I haven't tried other JDK/VM versions/VM options so far.

Java & native stack traces are attached.

How to reproduce:
1) ssh vmsqe-core2q-15
2) cd /net/vmsqe.russia/export/home/vi158347/PCL
3) run rerun.sh multiple times

The following tests are affected:
runtime/ParallelClassLoading/delegate-system/dynamic-init/abstract
runtime/ParallelClassLoading/delegate-system/dynamic-init/inner-complex