3.4. 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 */
   }
  

3.4.1. 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 */
}

3.4.2. 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 */
}

3.4.3. 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.