code: private static Set getListeners(final String busName) {
  
          final String methodName = "getListeners";
          if (TRACE.isEntryEnabled()) {
              SibTr.entry(TRACE, methodName, busName);
          }
  
          final Set listeners = new HashSet();
  
          synchronized (MESSAGING_ENGINE_LISTENERS) {
  
              // Get listeners for the particular bus
              final Set busListeners = (Set) MESSAGING_ENGINE_LISTENERS
                      .get(busName);
              if (busListeners != null) {
                  listeners.addAll(busListeners);
              }
  
              // Get listeners for all busses
              final Set noBusListeners = (Set) MESSAGING_ENGINE_LISTENERS
                      .get(null);
              if (noBusListeners != null) {
                  listeners.addAll(noBusListeners);
              }
  
          }
  
          if (TRACE.isEntryEnabled()) {
              SibTr.exit(TRACE, methodName, listeners);
          }
          return listeners;
  
      }
docs: Returns the set of listeners for the given bus.
  
  @param busName
  the name of the bus
  @return the listeners for that bus or the empty set if there are none.