4.5.2 Participant Library

A participant library provides a way to organize a set of participants belonging to the same system. A participant configuration specifies all the entities that a DomainParticipant created from this configuration will contain.

Figure 4.6: Participant Library Tag

Figure 4.6: Participant Library Tag, Table 4.7 Participant Library Tag, and Table 4.8 Domain Participant Tag show the description of a <domain_participant_library> and the tags it contains.

A <domain_participant> can be associated with a domain where topics and their associated types are already defined. The elements <register_type> and <topic> may also be defined in a <domain_participant>—the same way it is done in a <domain>. This makes it possible to add Topics, data-types, etc. beyond the ones defined in the domain, or alternatively redefine the elements that are already in the <domain>.

A <domain_participant> is defined by specifying the set of Entities it contains. This is done using tags such as <publisher>, <subscriber>, <data_writer> and <data_reader>, which specify an Entity of their corresponding type. These Entities are created within the DomainParticipant instantiated from the configuration profile that contains the definitions.

A <domain_participant> may inherit its configuration from another “base participant” specified using the base_name attribute. In this case, overriding applies to the base <domain_participant> as well as to the referred <domain>.

Note that in DataWriters always belong to a Publisher and DataReaders to a Subscriber. For this reason the <data_writer> and <data_reader> typically appear nested inside the corresponding <publisher> and <subscriber> tags. However, for convenience, it is possible to define <data_writer> and <data_reader> tags directly under the <domain_participant> tag. In this case, the DataWriters and DataReaders are created inside the implicit Publisher and Subscriber, respectively.

<domain_participant name="test">
    <memory_management>
	<sample_buffer_min_size>
		X
	</sample_buffer_min_size>
	<sample_buffer_trim_to_size>
		true
	</sample_buffer_trim_to_size>
    </memory_management>
    ...

The <publisher>, <subscriber>, <data_writer>, and <data_reader> tags are described in Figure 4.7: Publisher and Subscriber Tags , Table 4.9 Publisher Tag, Table 4.10 Subscriber Tag, Table 4.11 DataWriter Tag and Table 4.12 DataReader Tags.

Figure 4.7: Publisher and Subscriber Tags

The <publisher> tag defines by default a Publisher. It may contain a QoS configuration and several DataWriters. Likewise, the <subscriber> tag defines by default a Subscriber. It may contain a QoS configuration and several DataReaders.

The <filter> tag within a <data_reader> enables content filtering. It causes the corresponding DataReader to be created from a ContentFilteredTopic with the specified filter characteristics.

The ContentFilteredTopic name is generated as follows: xml_filter_name::xml_topic_name.

Where xml_filter_name is the value of the attribute name of the <filter> tag, and xml_topic_name is the value of the attribute name of the referred <topic> tag.

<parameter_list>
    <param>param_0</param>
    <param>param_1</param>
    ...
</parameter_list>

For example:

<domain_participant name="MyParticipant" 
 domain_ref="MyDomainLibrary::MyDomain">
	<publisher name="MyPublisher">
		<data_writer name="MyWriter" topic_ref="MyTopic"/>
	</publisher>

	<subscriber name="MySubscriber">
		<data_reader name="MyReader" topic_ref="MyTopic">
			<filter name="MyFilter" kind="builtin.sql">
				<expression> count &gt; %0 </expression>
				<parameter_list>
					<param>10<param>
				</parameter_list>
			</filter>
		</data_reader>
	</subscriber>
</domain_participant>

The above configuration defines a <domain_participant> that is bound to the <domain> “MyDomain”.

A DomainParticipant created from this configuration will contain:

• A Publisher which has a DataWriter created from the Topic “MyTopic”.
• A Subscriber which has DataReader created from a ContentFilteredTopic whose related Topic, “MyTopic”, uses a SQL filter. The ContentFilteredTopic has the name “MyTopic::MyFilter”.