Subscriber Use Cases

Working with subscribers. More...

Working with subscribers.

Setting up a subscriber

• Set up participant

• Create a Subscriber

  SubscriberQos subscriber_qos = new SubscriberQos();
  SubscriberListener subscriber_listener = null;
  
  try {
      participant.get_default_subscriber_qos(subscriber_qos);
  } catch (DDS.Exception) {
      Console.WriteLine(
          "***Error: failed to get default subscriber qos");
  }
  
  Subscriber subscriber = participant.create_subscriber(
      subscriber_qos,
      subscriber_listener,
      StatusMask.STATUS_MASK_NONE);
  if (subscriber == null) {
      Console.WriteLine(
          "***Error: failed to create subscriber");
  }

Set up subscriber to access received data

• Set up subscriber

• Set up to handle the DATA_ON_READERS_STATUS status, in one or both of the following two ways.

• Enable DATA_ON_READERS_STATUS for the SubscriberListener associated with the subscriber
  • The processing to handle the status change is done in the SubscriberListener.on_data_on_readers() method of the attached listener.
  • Typical processing will access the received data, either in arbitrary order or in a coherent and ordered manner.

• Enable DATA_ON_READERS_STATUS for the StatusCondition associated with the subscriber
  • The processing to handle the status change is done when the subscriber's attached status condition is triggered and the DATA_ON_READERS_STATUS status on the subscriber is changed.
  • Typical processing will access the received data, either in an arbitrary order or in a coherent and ordered manner.

Access received data via a subscriber

• Ensure subscriber is set up to access received data

• Get the list of readers that have data samples available:

  // holder for list/set of readers
  DataReaderSeq reader_seq = new DataReaderSeq();
  int max_samples = ResourceLimitsQosPolicy.LENGTH_UNLIMITED;
  SampleStateKind sample_state_mask =
      SampleStateKind.ANY_SAMPLE_STATE;
  ViewStateKind view_state_mask = ViewStateKind.ANY_VIEW_STATE;
  InstanceStateKind instance_state_mask =
      InstanceStateKind.ANY_INSTANCE_STATE;
  
  try {
      subscriber.get_datareaders(
          reader_seq, 
              sample_state_mask,
              view_state_mask, 
              instance_state_mask);
  } catch (DDS.Exception) {
      Console.WriteLine(
          "***Error: failed to access received data via subscriber");
      return;
  }

• Upon successfully getting the list of readers with data, process the data readers to either:
  • Read the data in each reader, OR
  • Take the data in each reader
  If the intent is to access the data coherently or in order, the list of data readers must be processed in the order returned:

  for (int i = 0; i < reader_seq.length; ++i) {
      DataReader reader = reader_seq.get_at(i);
  
    // Take the data from reader, 
    //            OR
    // Read the data from reader
  }

• Alternatively, call Subscriber.notify_datareaders() to invoke the DataReaderListener for each of the data readers.

  try {
          subscriber.notify_datareaders();
  } catch (DDS.Exception) {
      Console.WriteLine(
          "***Error: failed to notify datareaders");
  }

Access received data coherently and/or in order

To access the received data coherently and/or in an ordered manner, according to the settings of the PresentationQosPolicy attached to a Subscriber:

• Ensure subscriber is set up to access received data

• Indicate that data will be accessed via the subscriber:

  try {
      subscriber.begin_access();
  } catch (DDS.Exception) {
      // ... check for cause of failure
  } 

• Access received data via the subscriber, making sure that the data readers are processed in the order returned.

• Indicate that the data access via the subscriber is done:

  try {
      subscriber.end_access();
  } catch (DDS.Exception) {
      // ... check for cause of failure
  } 

Tearing down a subscriber

• Delete Subscriber:

  try {
      participant.delete_subscriber(ref subscriber);
  } catch (DDS.Exception) {
      Console.WriteLine(
          "***Error: failed to delete subscriber");
  }