@Override
        public boolean equals(Object obj) {
            if (this == obj) return true;
            if (!(obj instanceof IdentityKey<?>)) return false;
            IdentityKey<?> other = (IdentityKey<?>) obj;
            return this.instance == other.instance;
        }
A simplified {@link ConcurrentMap} using reference-equality to compare keys (similarly to {@link java.util.IdentityHashMap})

@author bjorncs
container-core/src/main/java/com/yahoo/jdisc/http/server/jetty/SimpleConcurrentIdentityHashMap.java