private void writeObject(ObjectOutputStream s) throws IOException {
    s.defaultWriteObject();
    s.writeObject(snapshot);
  }
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