static O collectionMutex(O o) {
  if (o instanceof L) ret o;
  
  S c = className(o);
  if (eq(c, "java.util.TreeMap$KeySet"))
    c = className(o = getOpt(o, 'm));
  else if (eq(c, "java.util.HashMap$KeySet"))
    c = className(o = get_raw(o, 'this$0));

  ifdef collectionMutex_debug
    print("Class name: " + className(o));
  endifdef
  
  if (eqOneOf(c, "java.util.TreeMap$AscendingSubMap", "java.util.TreeMap$DescendingSubMap"))
    c = className(o = get_raw(o, 'm));
    
  ifclass WeakHashSet
  if (o instanceof WeakHashSet)
    c = className(o = o/WeakHashSet.mutex());
  endif
    
  ret o;
}