Running test_respond_to.rb in a loop with a fastdebug build can results in the following assert:

terminus:~/jruby$ while [ $? -eq 0 ]; do jruby -J-showversion -J-d64 --server -J-XX:+UseCompressedOops -J-Xcomp -J-XX:+DeoptimizeRandom test/test_respond_to.rb ; done
...
java version "1.8.0-ea"
Java(TM) SE Runtime Environment (build 1.8.0-ea-b71)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b15-internal-fastdebug, compiled mode)

Run options:

# Running tests:

.# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=/compiledIC.cpp:567
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/home/cthaling/8005418/src/share/vm/code/compiledIC.cpp:567), pid=13735, tid=93
# assert(method_holder->data() == 0 || method_holder->data() == (intptr_t)callee()) failed: a) MT-unsafe modification of inline cache
#
# JRE version: Java(TM) SE Runtime Environment (8.0-b71) (build 1.8.0-ea-b71)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (25.0-b15-internal-fastdebug compiled mode solaris-sparc compressed oops)
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# An error report file with more information is saved as:
# /home/cthaling/jruby/hs_err_pid13735.log
 Locks owned:
Mutex: [0x10017a218/0x1] Patching_lock - owner: 0x105cc1800
Mutex: [0x10017bf58/0x101f75e01] CompiledIC_lock - owner: 0x105cc1800
 Locks owned:
Mutex: [0x10017a218/0x1] Patching_lock - owner: 0x105cc1800
Mutex: [0x10017bf58/0x101f75e01] CompiledIC_lock - owner: 0x105cc1800
#
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
#
Current thread is 93
Dumping core ...
Abort