Subscriber Use Cases
[Programming How-To's]

Working with subscribers. More...

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");
    }