public synchronized void clean() {
final Iterator<Map.Entry<K, WeakReferenceListManager<V>>> iterator =
mData.entrySet().iterator();
while (iterator.hasNext()) {
final Map.Entry<K, WeakReferenceListManager<V>> entry = iterator.next();
final WeakReferenceListManager<V> list = entry.getValue();
list.clean();
if (list.isEmpty()) {
iterator.remove();
}
}
}
