From http://stackoverflow.com/questions/35563250/attempting-to-make-nashorn-thread-safe

When using a Nashorn engine with multiple bindings some JavaScript methods throw a java.lang.ClassCastException when turning megamorphic. It seems that megamorphic access does not work with specialized LinkLogic introduced in 8u40. The attached Test class can be used to reproduce this. It generates the exception below.

Exception in thread "main" java.lang.ClassCastException: jdk.nashorn.internal.objects.NativeRegExpExecResult cannot be cast to jdk.nashorn.internal.objects.NativeArray
at jdk.nashorn.internal.objects.NativeArray.getContinuousArrayDataCCE(NativeArray.java:1898)
at jdk.nashorn.internal.objects.NativeArray.popObject(NativeArray.java:945)
at jdk.nashorn.internal.runtime.ScriptFunctionData.invoke(ScriptFunctionData.java:656)
at jdk.nashorn.internal.runtime.ScriptFunction.invoke(ScriptFunction.java:229)
at jdk.nashorn.internal.runtime.ScriptRuntime.apply(ScriptRuntime.java:387)
at jdk.nashorn.internal.scripts.Script$\^eval\_.:program(<eval>:1)
at jdk.nashorn.internal.runtime.ScriptFunctionData.invoke(ScriptFunctionData.java:636)
at jdk.nashorn.internal.runtime.ScriptFunction.invoke(ScriptFunction.java:229)
at jdk.nashorn.internal.runtime.ScriptRuntime.apply(ScriptRuntime.java:387)
at jdk.nashorn.api.scripting.NashornScriptEngine.evalImpl(NashornScriptEngine.java:437)
at jdk.nashorn.api.scripting.NashornScriptEngine.evalImpl(NashornScriptEngine.java:401)
at jdk.nashorn.api.scripting.NashornScriptEngine.evalImpl(NashornScriptEngine.java:397)
at jdk.nashorn.api.scripting.NashornScriptEngine.eval(NashornScriptEngine.java:152)
at javax.script.AbstractScriptEngine.eval(AbstractScriptEngine.java:264)
at Test.executeMethod(Test.java:21)
at Test.main(Test.java:14)