4.5. Create DomainParticipant, Topic, and Type¶

A DomainParticipantFactory creates DomainParticipants, and a DomainParticipant itself is the factory for creating Publishers, Subscribers, and Topics.

When creating a DomainParticipant, you may need to customize DomainParticipantQos, notably for:

Resource limits. Default resource limits are set at minimum values.
Initial peers.
Discovery. The name of the registered discovery component (“dpde” or “dpse”) must be assigned to DiscoveryQosPolicy’s name.
Participant Name. Every DomainParticipant is given the same default name. Must be unique when using DPSE discovery.

Example code:

Create a DomainParticipant with configured DomainParticipantQos:

DDS_DomainParticipant *participant = NULL;
struct DDS_DomainParticipantQos dp_qos =
     DDS_DomainParticipantQos_INITIALIZER;

/* DDS domain of DomainParticipant */
DDS_Long domain_id = 0;

/* Name of your registered Discovery component */
if (!RT_ComponentFactoryId_set_name(&dp_qos.discovery.discovery.name, "dpde"))
{
     /* failure */
}

/* Initial peers: use only default multicast peer */
DDS_StringSeq_set_maximum(&dp_qos.discovery.initial_peers,1);
DDS_StringSeq_set_length(&dp_qos.discovery.initial_peers,1);
*DDS_StringSeq_get_reference(&dp_qos.discovery.initial_peers,0) =
    DDS_String_dup("239.255.0.1");

/* Resource limits */
dp_qos.resource_limits.max_destination_ports = 32;
dp_qos.resource_limits.max_receive_ports = 32;
dp_qos.resource_limits.local_topic_allocation = 1;
dp_qos.resource_limits.local_type_allocation = 1;
dp_qos.resource_limits.local_reader_allocation = 1;
dp_qos.resource_limits.local_writer_allocation = 1;
dp_qos.resource_limits.remote_participant_allocation = 8;
dp_qos.resource_limits.remote_reader_allocation = 8;
dp_qos.resource_limits.remote_writer_allocation = 8;

/* Participant name */
strcpy(dp_qos.participant_name.name, "Participant_1");

participant =
     DDS_DomainParticipantFactory_create_participant(factory,
                                                     domain_id,
                                                     &dp_qos,
                                                     NULL,
                                                     DDS_STATUS_MASK_NONE);
 if (participant == NULL)
 {
     /* failure */
 }

4.5.1. Register Type¶

Your data types that have been generated from IDL need to be registered with the DomainParticipants that will be using them. Each registered type must have a unique name, preferably the same as its IDL defined name.

DDS_ReturnCode_t retcode;

retcode = DDS_DomainParticipant_register_type(participant,
                                              "HelloWorld",
                                              HelloWorldTypePlugin_get());
if (retcode != DDS_RETCODE_OK)
{
    /* failure */
}

4.5.2. Create Topic of Registered Type¶

DDS Topics encapsulate the types being communicated, and you can create Topics for your type once your type is registered.

A topic is given a name at creation (e.g. “Example HelloWorld”). The type associated with the Topic is specified with its registered name.

DDS_Topic *topic = NULL;

topic = DDS_DomainParticipant_create_topic(participant,
                                           "Example HelloWorld",
                                           "HelloWorld",
                                           &DDS_TOPIC_QOS_DEFAULT,
                                           NULL,
                                           DDS_STATUS_MASK_NONE);

if (topic == NULL)
{
    /* failure */
}

4.5.3. DPSE Discovery: Assert Remote Participant¶

DPSE Discovery relies on the application to specify the other, or remote, DomainParticipants that its local DomainParticipants are allowed to discover. Your application must call a DPSE API for each remote participant to be discovered. The API takes as input the name of the remote participant.

/* Enable discovery of remote participant with name Participant_2 */
retcode = DPSE_RemoteParticipant_assert(participant, "Participant_2");
if (retcode != DDS_RETCODE_OK)
{
    /* failure */
}

For more information, see the DDS Domains section in the User’s Manual.