docs: public void addWatcher(String name, Watcher watcher){
          if(LOGGER.isTraceEnabled()){
              LOGGER.trace("Add a watcher, name={}", name);
          }
  
          synchronized(watchers){
  
              if (watchers.containsKey(name)) {
                  watchers.get(name).add(watcher);
              } else {
                  Set<Watcher> set = new HashSet<Watcher>();
                  set.add(watcher);
                  watchers.put(name, set);
              }
          }
      }