code: public static void unregister (PerformanceObserver obs, String name)
      {
          // get the observer's action hashtable
          Map<String, PerformanceAction> actions = _observers.get(obs);
          if (actions == null) {
              log.warning("Attempt to unregister by unknown observer " +
                          "[observer=" + obs + ", name=" + name + "].");
              return;
          }
  
          // attempt to remove the specified action
          PerformanceAction action = actions.remove(name);
          if (action == null) {
              log.warning("Attempt to unregister unknown action " +
                          "[observer=" + obs + ", name=" + name + "].");
              return;
          }
  
          // if the observer has no actions left, remove the observer's action
          // hash in its entirety
          if (actions.size() == 0) {
              _observers.remove(obs);
          }
      }
docs: Un-register the named action associated with the given observer.
  
  @param obs the action observer.
  @param name the action name.