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();
  
    // MySubscriberListener is user defined and 
    // implements SubscriberListener
    SubscriberListener subscriber_listener
        = new MySubscriberListener(); // or = null
  
    participant.get_default_subscriber_qos(subscriber_qos);
  
    Subscriber subscriber = null;
    try {
        subscriber = participant.create_subscriber(subscriber_qos, 
                                                   subscriber_listener,
                                                   StatusKind.STATUS_MASK_ALL);
    } catch (RETCODE_ERROR err) {
        // respond to exception
    }
  

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 com.rti.dds.subscription.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:

    DataReaderSeq reader_seq = new DataReaderSeq(); // list of readers
    int max_samples = DataReader.LENGTH_UNLIMITED;
    int  sample_state_mask = SampleStateKind.NOT_READ_SAMPLE_STATE;
    int  view_state_mask = ViewStateKind.ANY_VIEW_STATE;
    int  instance_state_mask = InstanceStateKind.ANY_INSTANCE_STATE;
     
    try {
        subscriber.get_datareaders(reader_seq, 
                                   sample_state_mask,
                                   view_state_mask, 
                                   instance_state_mask);
    } catch (RETCODE_ERROR err) {
        // handle exception
    }
  

• 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.size(); ++i) {
        FooDataReader reader = (FooDataReader) reader_seq.get(i);
        // Take the data from reader, 
        //            OR
        // Read the data from reader
    }
  

• Alternatively, call com.rti.dds.subscription.Subscriber.notify_datareaders to invoke the DataReaderListener for each of the data readers.

      subscriber.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 com.rti.dds.infrastructure.PresentationQosPolicy attached to a com.rti.dds.subscription.Subscriber:

• Ensure subscriber is set up to access received data

• Indicate that data will be accessed via the subscriber:

    subscriber.begin_access();
  

• 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:

    subscriber.end_access();
  

Tearing down a subscriber

• Delete Subscriber:

    try {
        participant.delete_subscriber(subscriber);
    } catch (RETCODE_ERROR err) {
        // handle exception
    }