code: public void addTangoPeriodicListener(ITangoPeriodicListener listener, String attrName, String[] filters, boolean stateless)
              throws DevFailed {
          TangoPeriodic tangoPeriodic;
  
          String key = deviceName+"/"+attrName;
          if ((tangoPeriodic = tango_periodic_source.get(key)) == null) {
              tangoPeriodic = new TangoPeriodic(deviceProxy, attrName, filters);
              tango_periodic_source.put(key, tangoPeriodic);
          }
  
          synchronized (moni) {
              tangoPeriodic.addTangoPeriodicListener(listener, stateless);
          }
      }
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