I filed https://bugs.openjdk.java.net/browse/JDK-8200258 and added comment:
I agree that CopyOnWriteArrayList subList code can be improved. We should stop subclassing AbstractList. We should add more tests. We should have more guidance about when to use index-based API - only when quiescent or thread-confined. Explain how to most efficiently create a snapshot - probably snapshot = new CopyOnWriteArrayList(sharedCOWAL)
