code: function add(message) {
          if (!message.order || // no keep order needed
                  message.inProcess) {// or already in process
              return false; // should continue
          }
  
          var queue = this.getQueue(message.context);
          queue.unshift(message); // FIFO
          message.pointId = this.pipe._id;
          var moreInQueue = queue.length > 1;
          message.inProcess = !moreInQueue;
  
          return moreInQueue;
      }
docs: return true, if message prcessing should be paused