5.3.5. DomainParticipantListener Discovery Callbacks

As stated in DomainParticipantListener, the DomainParticipantListener is an abstract class defining the callbacks that will be triggered in response to state changes on the DomainParticipant. Fast DDS defines four callbacks attached to events that may occur during discovery: on_participant_discovery(), on_subscriber_discovery(), on_publisher_discovery(), on_type_discovery(). Further information about the DomainParticipantListener is provided in the DomainParticipantListener section. The following is an example of the implementation of DomainParticipantListener discovery callbacks.

class DiscoveryDomainParticipantListener : public DomainParticipantListener
{
    /* Custom Callback on_participant_discovery */
    void on_participant_discovery(
            DomainParticipant* participant,
            eprosima::fastrtps::rtps::ParticipantDiscoveryInfo&& info) override
    {
        static_cast<void>(participant);
        switch (info.status){
            case eprosima::fastrtps::rtps::ParticipantDiscoveryInfo::DISCOVERED_PARTICIPANT:
                /* Process the case when a new DomainParticipant was found in the domain */
                std::cout << "New DomainParticipant '" << info.info.m_participantName <<
                    "' with ID '" << info.info.m_guid.entityId << "' and GuidPrefix '" <<
                    info.info.m_guid.guidPrefix << "' discovered." << std::endl;
                break;
            case eprosima::fastrtps::rtps::ParticipantDiscoveryInfo::CHANGED_QOS_PARTICIPANT:
                /* Process the case when a DomainParticipant changed its QOS */
                break;
            case eprosima::fastrtps::rtps::ParticipantDiscoveryInfo::REMOVED_PARTICIPANT:
                /* Process the case when a DomainParticipant was removed from the domain */
                std::cout << "New DomainParticipant '" << info.info.m_participantName <<
                    "' with ID '" << info.info.m_guid.entityId << "' and GuidPrefix '" <<
                    info.info.m_guid.guidPrefix << "' left the domain." << std::endl;
                break;
        }
    }

    /* Custom Callback on_subscriber_discovery */
    void on_subscriber_discovery(
            DomainParticipant* participant,
            eprosima::fastrtps::rtps::ReaderDiscoveryInfo&& info) override
    {
        static_cast<void>(participant);
        switch (info.status){
            case eprosima::fastrtps::rtps::ReaderDiscoveryInfo::DISCOVERED_READER:
                /* Process the case when a new subscriber was found in the domain */
                std::cout << "New DataReader subscribed to topic '" << info.info.topicName() <<
                    "' of type '" << info.info.typeName() << "' discovered";
                break;
            case eprosima::fastrtps::rtps::ReaderDiscoveryInfo::CHANGED_QOS_READER:
                /* Process the case when a subscriber changed its QOS */
                break;
            case eprosima::fastrtps::rtps::ReaderDiscoveryInfo::REMOVED_READER:
                /* Process the case when a subscriber was removed from the domain */
                std::cout << "New DataReader subscribed to topic '" << info.info.topicName() <<
                    "' of type '" << info.info.typeName() << "' left the domain.";
                break;
        }
    }

    /* Custom Callback on_publisher_discovery */
    void on_publisher_discovery(
            DomainParticipant* participant,
            eprosima::fastrtps::rtps::WriterDiscoveryInfo&& info) override
    {
        static_cast<void>(participant);
        switch (info.status){
            case eprosima::fastrtps::rtps::WriterDiscoveryInfo::DISCOVERED_WRITER:
                /* Process the case when a new publisher was found in the domain */
                std::cout << "New DataWriter publishing under topic '" << info.info.topicName() <<
                    "' of type '" << info.info.typeName() << "' discovered";
                break;
            case eprosima::fastrtps::rtps::WriterDiscoveryInfo::CHANGED_QOS_WRITER:
                /* Process the case when a publisher changed its QOS */
                break;
            case eprosima::fastrtps::rtps::WriterDiscoveryInfo::REMOVED_WRITER:
                /* Process the case when a publisher was removed from the domain */
                std::cout << "New DataWriter publishing under topic '" << info.info.topicName() <<
                    "' of type '" << info.info.typeName() << "' left the domain.";
                break;
        }
    }

    /* Custom Callback on_type_discovery */
    void on_type_discovery(
            DomainParticipant* participant,
            const eprosima::fastrtps::rtps::SampleIdentity& request_sample_id,
            const eprosima::fastrtps::string_255& topic,
            const eprosima::fastrtps::types::TypeIdentifier* identifier,
            const eprosima::fastrtps::types::TypeObject* object,
            eprosima::fastrtps::types::DynamicType_ptr dyn_type) override
    {
        static_cast<void>(participant);
        static_cast<void>(request_sample_id);
        static_cast<void>(topic);
        static_cast<void>(identifier);
        static_cast<void>(object);
        static_cast<void>(dyn_type);
        std::cout << "New data type of topic '" << topic << "' discovered." << std::endl;
    }

};

To use the previously implemented discovery callbacks in DiscoveryDomainParticipantListener class, which inherits from the DomainParticipantListener, an object of this class is created and registered as a listener of the DomainParticipant.

// Create the participant QoS and configure values
DomainParticipantQos pqos;

// Create a custom user DomainParticipantListener
DiscoveryDomainParticipantListener* plistener = new DiscoveryDomainParticipantListener();
// Pass the listener on DomainParticipant creation.
DomainParticipant* participant =
        DomainParticipantFactory::get_instance()->create_participant(
    0, pqos, plistener);

Important

Read more about callbacks and its hierarchy here