Heads-up: guarantee(obj->mark() == markOopDesc::encode(mid)) failed

[Aleksey Shipilev]

Hey Roman,

I think ShenandoahMergeSafepointCleanup has a bug somewhere, because this seems
to fail with moderate frequency:

$ build/linux-x86_64-normal-server-fastdebug/images/jdk/bin/java -jar
~/Install/jcstress/jcstress-tests-all-2017-06-12.jar --jvmArgs
"-XX:+UseShenandoahGC -XX:ShenandoahGCHeustics=aggressive
-XX:+UnlockExperimentalVMOptions -XX:+ShenandoahMergeSafepointCleanup" -t
WeakReference -m stress


#  Internal Error
(/home/shade/trunks/shenandoah-jdk9/hotspot/src/share/vm/runtime/synchronizer.cpp:1611),
pid=12272, tid=12292
#  guarantee(obj->mark() == markOopDesc::encode(mid)) failed: invariant


http://cr.openjdk.java.net/~shade/shenandoah/hs_err_pid12272.log

Please take a look?

Thanks,
-Aleksey