}
public void addIncludingHierarchy(IncludedModule hierarchy) {
synchronized (getRuntime().getHierarchyLock()) {
Set<RubyClass> oldIncludingHierarchies = includingHierarchies;
if (oldIncludingHierarchies == Collections.EMPTY_SET) includingHierarchies = oldIncludingHierarchies = new WeakHashSet(4);
oldIncludingHierarchies.add(hierarchy);
}
}