code: private synchronized LinkedHashSet<IMessageCallback> getCallbacks(String channel, boolean autoCreate, boolean clone) {
          LinkedHashSet<IMessageCallback> result = callbacks.get(channel);
          
          if (result == null && autoCreate) {
              callbacks.put(channel, result = new LinkedHashSet<>());
          }
          
          return result == null ? null : clone ? new LinkedHashSet<>(result) : result;
      }
docs: Return the callbacks associated with the specified channel.
  
  @param channel The channel.
  @param autoCreate Create the callback list if one doesn't exist.
  @param clone Return a clone of the callback list.
  @return The callback list (possibly null).