@Override
 public boolean addAll(TDoubleCollection coll) {
   synchronized (mutex) {
     return c.addAll(coll);
   }
 }
 @Override
 public boolean addAll(double[] array) {
   synchronized (mutex) {
     return c.addAll(array);
   }
 }
 @Override
 public boolean addAll(Collection<? extends Double> coll) {
   synchronized (mutex) {
     return c.addAll(coll);
   }
 }