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 three callbacks attached to events that may occur during discovery: on_participant_discovery(), on_data_reader_discovery(), on_data_writer_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::fastdds::rtps::ParticipantDiscoveryStatus status,
            const ParticipantBuiltinTopicData& info,
            bool& should_be_ignored) override
    {
        should_be_ignored = false;
        static_cast<void>(participant);
        switch (status){
            case eprosima::fastdds::rtps::ParticipantDiscoveryStatus::DISCOVERED_PARTICIPANT:
            {
                /* Process the case when a new DomainParticipant was found in the domain */
                std::cout << "New DomainParticipant '" << info.participant_name <<
                    "' with ID '" << info.guid.entityId << "' and GuidPrefix '" <<
                    info.guid.guidPrefix << "' discovered." << std::endl;
                /* The following line can be substituted to evaluate whether the discovered participant should be ignored */
                bool ignoring_condition = false;
                if (ignoring_condition)
                {
                    should_be_ignored = true;     // Request the ignoring of the discovered participant
                }
            }
            break;
            case eprosima::fastdds::rtps::ParticipantDiscoveryStatus::CHANGED_QOS_PARTICIPANT:
                /* Process the case when a DomainParticipant changed its QOS */
                break;
            case eprosima::fastdds::rtps::ParticipantDiscoveryStatus::REMOVED_PARTICIPANT:
                /* Process the case when a DomainParticipant was removed from the domain */
                std::cout << "DomainParticipant '" << info.participant_name <<
                    "' with ID '" << info.guid.entityId << "' and GuidPrefix '" <<
                    info.guid.guidPrefix << "' left the domain." << std::endl;
                break;
        }
    }

    /* Custom Callback on_data_reader_discovery */
    void on_data_reader_discovery(
            DomainParticipant* participant,
            eprosima::fastdds::rtps::ReaderDiscoveryStatus reason,
            const eprosima::fastdds::rtps::SubscriptionBuiltinTopicData& info,
            bool& should_be_ignored) override
    {
        should_be_ignored = false;
        static_cast<void>(participant);
        switch (reason){
            case eprosima::fastdds::rtps::ReaderDiscoveryStatus::DISCOVERED_READER:
            {
                /* Process the case when a new datareader was found in the domain */
                std::cout << "New DataReader subscribed to topic '" << info.topic_name <<
                    "' of type '" << info.type_name << "' discovered";
                /* The following line can be substituted to evaluate whether the discovered datareader should be ignored */
                bool ignoring_condition = false;
                if (ignoring_condition)
                {
                    should_be_ignored = true;     // Request the ignoring of the discovered datareader
                }
            }
            break;
            case eprosima::fastdds::rtps::ReaderDiscoveryStatus::CHANGED_QOS_READER:
                /* Process the case when a datareader changed its QOS */
                break;
            case eprosima::fastdds::rtps::ReaderDiscoveryStatus::REMOVED_READER:
                /* Process the case when a datareader was removed from the domain */
                std::cout << "DataReader subscribed to topic '" << info.topic_name <<
                    "' of type '" << info.type_name << "' left the domain.";
                break;
        }
    }

    /* Custom Callback on_data_writer_discovery */
    void on_data_writer_discovery(
            DomainParticipant* participant,
            eprosima::fastdds::rtps::WriterDiscoveryStatus reason,
            const eprosima::fastdds::dds::PublicationBuiltinTopicData& info,
            bool& should_be_ignored) override
    {
        should_be_ignored = false;
        static_cast<void>(participant);
        switch (reason){
            case eprosima::fastdds::rtps::WriterDiscoveryStatus::DISCOVERED_WRITER:
            {
                /* Process the case when a new datawriter was found in the domain */
                std::cout << "New DataWriter publishing under topic '" << info.topic_name <<
                    "' of type '" << info.type_name << "' discovered";
                /* The following line can be substituted to evaluate whether the discovered datawriter should be ignored */
                bool ignoring_condition = false;
                if (ignoring_condition)
                {
                    should_be_ignored = true;     // Request the ignoring of the discovered datawriter
                }
            }
            break;
            case eprosima::fastdds::rtps::WriterDiscoveryStatus::CHANGED_QOS_WRITER:
                /* Process the case when a datawriter changed its QOS */
                break;
            case eprosima::fastdds::rtps::WriterDiscoveryStatus::REMOVED_WRITER:
                /* Process the case when a datawriter was removed from the domain */
                std::cout << "DataWriter publishing under topic '" << info.topic_name <<
                    "' of type '" << info.type_name << "' left the domain.";
                break;
        }
    }

};

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