/** {@inheritDoc} */
 @Override
 public synchronized void incrAllCounters(AbstractCounters<Counter, CounterGroup> other) {
   for (CounterGroup group : other) {
     for (Counter counter : group) {
       findCounter(group.getName(), counter.getName()).increment(counter.getValue());
     }
   }
 }
 /** {@inheritDoc} */
 @Override
 public synchronized CounterGroup addGroup(CounterGroup grp) {
   return addGroup(grp.getName(), grp.getDisplayName());
 }