@SuppressWarnings("unchecked")
  private void readObject(ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
    s.defaultReadObject();
    snapshot = (Set<T>) s.readObject();
  }
Return a snapshot of the set at this point in time. The snapshot is guaranteed not to change.
It is therefore unmodifiable. This will likely be more efficient than copying this set.

@return A snapshot of this set.
geode-core/src/main/java/org/apache/geode/internal/CopyOnWriteHashSet.java