code: public static synchronized void addListener(int fileDescriptor, SerialInterruptListener listener) {
          if (!listeners.containsKey(fileDescriptor)) {
              listeners.put(fileDescriptor, listener);
              enableSerialDataReceiveCallback(fileDescriptor);
          }
      }
docs: <p>
  Java consumer code can all this method to register itself as a listener for pin state
  changes.
  </p>
  
  @see com.pi4j.jni.SerialInterruptListener
  @see com.pi4j.jni.SerialInterruptEvent
  
  @param fileDescriptor the serial file descriptor/handle
  @param listener A class instance that implements the GpioInterruptListener interface.