MQTTService.sedona

**
** MQTT service (community version)
** MQTT service provides the following abilities:
**  1. publish data to a topic of a MQTT broker
**  2. subscribe topic data of a MQTT broker and update local sedona object
**  3. able to publish/subscribe multiple MQTT broker at the same time
** 
** Well, there are some limitations: 
**  1. it is a native kit, so svm need to be recompiled to use it 
**  2. TLS/SSL is not supported yet, so use it under trusted network environment
**  3. only Linux is supported, Windows is not supported right now
**
** If you don't want to set up a local MQTT broker, you can try some online brokers for testing:
**  1. test.mosquitto.org:1883 (http://test.mosquitto.org/)
**  2. broker.hivemq.com:1883 (https://www.hivemq.com/try-out/)
**
** If possible, we recommend you to set up a local MQTT broker by mosquitto(https://mosquitto.org/), 
** that is a popular and open source implementation of MQTT broker, it is fairly easy to set up under Linux. 
** 
class MQTTService extends Service
{
  ////////////////////////////////////////////////////////////////
  // Life cycle
  ////////////////////////////////////////////////////////////////

  **
  ** init and start MQTT service 
  **
  virtual override void start()
  {
    log.message("MQTT service started")
  }

  ** 
  ** stop MQTT service
  ** 
  virtual override void stop()
  {
    log.message("MQTT service stopped")
  }

  ////////////////////////////////////////////////////////////////
  // Methods
  ////////////////////////////////////////////////////////////////
  **
  ** Get first child component of type Worker (or subclass).
  ** Returns null if no Worker objects found.
  **
  private Worker getFirstWorker()
  {
    App app = Sys.app
    for (Component c = app.lookup(children); c != null; c = app.lookup(c.nextSibling))
      if (c.type.is(Worker.type))
        return (Worker)c
    return null
  }

  **
  ** Get next child component after 'worker' that is of type Worker (or subclass).
  ** Returns null if it reaches the end of the list without finding one.
  **
  private Worker getNextWorker(Worker worker)
  {
    App app = Sys.app
    for (Component c = app.lookup(worker.id); c != null; c = app.lookup(c.nextSibling))
      if (c.id != worker.id && c.type.is(Worker.type))
        return (Worker)c
    return null
  }

  override bool work() 
  {
    for(Worker w = getFirstWorker(); w != null; w = getNextWorker(w))
      w.work()
    return false
  } 

  ////////////////////////////////////////////////////////////////
  // Fields
  ////////////////////////////////////////////////////////////////
  define Log log
}