Got a not easily reproducible crash in deflate_idle_monitors. This occurred while running a test under jprt, solaris sparc product build.

# guarantee(mid->header()->is_neutral()) failed: invariant
V [libjvm.so+0x12e636c] bool ObjectSynchronizer::deflate_monitor(ObjectMonitor*,oopDesc*,ObjectMonitor**,ObjectMonitor**)+0x9c
V [libjvm.so+0x12e68b8] void ObjectSynchronizer::deflate_idle_monitors()+0xb8
V [libjvm.so+0x123053c] void SafepointSynchronize::do_cleanup_tasks()+0x8c
V [libjvm.so+0x123006c] void SafepointSynchronize::begin()+0x9ec
V [libjvm.so+0x13cc660] void VMThread::loop()+0x300
V [libjvm.so+0x13cbdc0] void VMThread::run()+0xa0
V [libjvm.so+0x112eefc] thread_native_entry+0x32c

VM_Operation is G1CollectFull.

This same failure seems to be reported every once in a while and always gets closed as not reproducible: see, for examples, JDK-6761397, JDK-8153904, JDK-8012266, JDK-8019160

See the attached hs_err file for more details.