return materializedAttributes;
}
private MultiWindowSpread getMultiWindowSpread(String key) {
MultiWindowSpread spread = spreads.get(key);
if (spread == null) {
spread = new MultiWindowSpread();
MultiWindowSpread existingSpreads = spreads.putIfAbsent(key, spread);
if (existingSpreads != null) {
spread = existingSpreads;
}
}