13.1.2. Statistics Domain Participant

In order to start collecting data in one of the statistics topics (Statistics Topic names), the corresponding statistics DataWriter should be enabled. In fact, Fast DDS Statistics module can be enabled and disabled at runtime. For this purpose, Fast DDS Statistics module exposes an extended DDS DomainParticipant API:

13.1.2.1. Enable statistics DataWriters

Statistics DataWriters can be enabled in different ways. It can be done automatically (see Automatically enabling statistics DataWriters). Alternatively, Statistics DataWriters can be enabled at run time using one of two methods: enable_statistics_datawriter() or enable_statistics_datawriter_with_profile().

enable_statistics_datawriter() method requires as parameters:

It is possible to define specific desired QoS through DataWriter profile on the FASTRTPS_DEFAULT_PROFILES_FILE (see XML profiles). enable_statistics_datawriter_with_profile() method enables a DataWriter by searching a specific DataWriter XML profile. On those profiles, specific QoS can be set.

enable_statistics_datawriter_with_profile() method requires as parameters:

  • Name of the XML profile to use to fill the QoS structure of the DataWriter.

  • Name of the statistics topic name to be enabled. (see Statistics Topic names for the statistics topic list).

13.1.2.2. Disable statistics DataWriters

Statistics DataWriters are disabled using the method disable_statistics_datawriter(). This method requires as parameter:

13.1.2.3. Obtain pointer to the extended DomainParticipant class

The DomainParticipant is created using the create_participant() provided by the DomainParticipantFactory. This method returns a pointer to the DDS standard DomainParticipant created. In order to obtain the pointer to the child DomainParticipant which extends the DDS API, the static method narrow() is provided.

13.1.2.4. Example

The following example shows how to use the Statistics module extended DDS API:

// Create a DomainParticipant
DomainParticipant* participant =
        DomainParticipantFactory::get_instance()->create_participant(0, PARTICIPANT_QOS_DEFAULT);
if (nullptr == participant)
{
    // Error
    return;
}

// Obtain pointer to child class
eprosima::fastdds::statistics::dds::DomainParticipant* statistics_participant =
        eprosima::fastdds::statistics::dds::DomainParticipant::narrow(participant);

// Enable statistics DataWriter
if (statistics_participant->enable_statistics_datawriter(eprosima::fastdds::statistics::GAP_COUNT_TOPIC,
        eprosima::fastdds::statistics::dds::STATISTICS_DATAWRITER_QOS) != ReturnCode_t::RETCODE_OK)
{
    // Error
    return;
}

// Use the DomainParticipant to communicate
// (...)

// Disable statistics DataWriter
if (statistics_participant->disable_statistics_datawriter(eprosima::fastdds::statistics::GAP_COUNT_TOPIC) !=
        ReturnCode_t::RETCODE_OK)
{
    // Error
    return;
}

// Delete DomainParticipant
if (DomainParticipantFactory::get_instance()->delete_participant(participant) != ReturnCode_t::RETCODE_OK)
{
    // Error
    return;
}

13.1.2.5. Automatically enabling statistics DataWriters

The statistics DataWriters can be directly enabled using the DomainParticipantQos properties() fastdds.statistics. The value of this property is a semicolon separated list containing the statistics topic name aliases of those DataWriters that the user wants to enable. The property can be set either programmatically or loading an XML file. If the property is set in both ways, the priority would depend on the API and the QoS profile provided:

Another way of enabling statistics DataWriters, compatible with the previous one, is setting the FASTDDS_STATISTICS environment variable. The statistics DataWriters that will be enabled when the DomainParticipant is enabled would be the union between those specified in the properties() fastdds.statistics and those included with the environment variable.

The following examples show how to use all the previous methods:

C++

 
DomainParticipantQos pqos;

// Activate Fast DDS Statistics module
pqos.properties().properties().emplace_back("fastdds.statistics",
        "HISTORY_LATENCY_TOPIC;ACKNACK_COUNT_TOPIC;DISCOVERY_TOPIC;PHYSICAL_DATA_TOPIC");

XML

 
<participant profile_name="statistics_domainparticipant_conf_xml_profile">
    <rtps>
        <propertiesPolicy>
            <properties>
                <!-- Activate Fast DDS Statistics Module -->
                <property>
                    <name>fastdds.statistics</name>
                    <value>HISTORY_LATENCY_TOPIC;ACKNACK_COUNT_TOPIC;DISCOVERY_TOPIC;PHYSICAL_DATA_TOPIC</value>
                </property>
            </properties>
        </propertiesPolicy>
    </rtps>
</participant>

Environment Variable Linux

 
export FASTDDS_STATISTICS="HISTORY_LATENCY_TOPIC;ACKNACK_COUNT_TOPIC;DISCOVERY_TOPIC;PHYSICAL_DATA_TOPIC"

Environment Variable Windows

 
set FASTDDS_STATISTICS=HISTORY_LATENCY_TOPIC;ACKNACK_COUNT_TOPIC;DISCOVERY_TOPIC;PHYSICAL_DATA_TOPIC

Note

These are all the statistics topics:

HISTORY_LATENCY_TOPIC;NETWORK_LATENCY_TOPIC;PUBLICATION_THROUGHPUT_TOPIC;SUBSCRIPTION_THROUGHPUT_TOPIC;RTPS_SENT_TOPIC;RTPS_LOST_TOPIC;HEARTBEAT_COUNT_TOPIC;ACKNACK_COUNT_TOPIC;NACKFRAG_COUNT_TOPIC;GAP_COUNT_TOPIC;DATA_COUNT_TOPIC;RESENT_DATAS_TOPIC;SAMPLE_DATAS_TOPIC;PDP_PACKETS_TOPIC;EDP_PACKETS_TOPIC;DISCOVERY_TOPIC;PHYSICAL_DATA_TOPIC

Note

Be aware that automatically enabling the statistics DataWriters using all these methods implies using the recommended QoS profile STATISTICS_DATAWRITER_QOS. For more information, please refer to Statistics DataWriter recommended QoS. However, if an XML profile is defined, the QoS applied are those defined in the profile, and for those QoS that are not specified in that profile, the default library QoS are applied (see DataWriterQos for the standard eProsima’s DataWriter QoS), and not the recommended QoS for the Statistics DataWriters.

For the creation of an automatically enabled Datawriter, the priority for setting its QoS is the following:

  • First, if a specific profile exists for the statistics topic, that one is applied.

  • If that is not the case but a generic profile for statistics DataWriters exists, that one is applied.

  • If no profile is defined in XML file, the recommended statistics QoS are applied.

Note

The generic DataWriter profile defined in the FASTRTPS_DEFAULT_PROFILES_FILE XML needs to be named as GENERIC_STATISTICS_PROFILE.

The specific DataWriter profile defined in the FASTRTPS_DEFAULT_PROFILES_FILE XML needs to be named using the same statistic topic alias or name (see Statistics Topic names for the alias corresponding to each statistic topic) that has been used in the DomainParticipantQos properties() fastdds.statistics (see Statistics Module Settings) or the FASTDDS_STATISTICS environment variable, where the enabling of the corresponding statistics topic has been set.