code: public void addTangoPipeListener(ITangoPipeListener listener,
                                       String attrName, String[] filters, boolean stateless) throws DevFailed {
          TangoPipe tangoPipe;
          String key = deviceName+"/"+attrName;
          if ((tangoPipe = tango_pipe_source.get(key)) == null) {
              tangoPipe = new TangoPipe(deviceProxy, attrName, filters);
              tango_pipe_source.put(key, tangoPipe);
          }
  
          synchronized (moni) {
              tangoPipe.addTangoPipeListener(listener, stateless);
          }
      }
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