DataWriter Use Cases

Working with data writers.

Working with data writers.

Setting up a data writer

• Set up publisher
• Set up a topic
• Create a data writer, FooDataWriter, of user data type Foo:

  struct DDS_DataWriterQos writer_qos = DDS_DataWriterQos_INITIALIZER;
  DDS_DataWriter* writer;
  struct DDS_DataWriterListener writer_listener =
      DDS_DataWriterListener_INITIALIZER;
   
  /* MyWriterListener_* functions are user defined to match
     DDS_DataWriterListener functions */
  writer_listener.on_offered_deadline_missed =
      MyWriterListener_OfferedDeadlineMissed;
  writer_listener.on_offered_incompatible_qos =
      MyWriterListener_OfferedIncompatibleQos;
  writer_listener.on_liveliness_lost = MyWriterListener_LivelinessLost;
  writer_listener.on_publication_match = MyWriterListener_PublicationMatch;
   
  retcode = DDS_Publisher_get_default_datawriter_qos(publisher, &writer_qos);
   
  if (retcode != DDS_RETCODE_OK) {
      printf("***Error: failed to get default datawriter qos\n");
  }
   
  writer = DDS_Publisher_create_datawriter(publisher, 
                                           topic, 
                                           &writer_qos, 
                                           &writer_listener /* or NULL */,
                                     DDS_STATUS_MASK_ALL);
   
  if (writer == NULL) {
      printf("***Error: failed to create writer\n");
  }

Managing instances

• Getting an instance "key" value of user data type Foo

  struct Foo* data = ...;     /* user data */
   
  retcode = FooDataWriter_get_key_value(writer, data, &instance_handle);
   
  if (retcode != DDS_RETCODE_OK) {
      /* ... check for cause of failure */
  }    

• Registering an instance of type Foo

  DDS_InstanceHandle_t instance_handle = DDS_HANDLE_NIL;
   
  instance_handle = FooDataWriter_register_instance(writer, data);

• Unregistering an instance of type Foo

  retcode = FooDataWriter_unregister_instance(writer, data, &instance_handle);
   
  if (retcode != DDS_RETCODE_OK) {
      /* ... check for cause of failure */
  }  

• Disposing of an instance of type Foo

  retcode = FooDataWriter_dispose(writer, data, &instance_handle);
   
  if (retcode != DDS_RETCODE_OK) {
      /* ... check for cause of failure */
  }  

Sending data

• Set up data writer
• Register instance
• Write instance of type Foo

  struct Foo* data = ...;     /* user data */
   
  DDS_InstanceHandle_t instance_handle = 
      DDS_HANDLE_NIL; /* or a valid registered handle */
   
  DDS_ReturnCode_t retcode;
   
  retcode = FooDataWriter_write(writer, data, &instance_handle);
   
  if (retcode != DDS_RETCODE_OK) {
      /* ... check for cause of failure */
  }

Tearing down a data writer

• Delete DDS_DataWriter:

  DDS_ReturnCode_t retcode;
   
  retcode = DDS_Publisher_delete_datawriter(publisher, writer);
   
  if (retcode != DDS_RETCODE_OK) {
      printf("***Error: failed to delete writer\n");
  }