Statuses¶

Entities in DDS have statuses that indicate the internal state and/or history of an entity. These statuses signal Waitsets and Listeners, and are different between types of DDS entities. The following table lists the fields for each status and their meaning:

CycloneDDS-CXX Status entities and fields¶
CDDS-CXX Entity Type	Status Entity	Associated Fields	Meaning of field
DomainParticipant
Publisher
Subscriber
Topic	InconsistentTopicStatus	total_count	the total number of times an inconsistent topic was encountered
Topic	InconsistentTopicStatus	total_count_change	the change in total_count since last being retrieved
DataWriter	OfferedDeadlineMissedStatus	total_count	the total number of times an offered deadline was missed by the writer committing itself to the deadline
		total_count_change	the change in total_count since last being retrieved
		last_instance_handle	handle to the last instance in a writer missing a committed deadline
	OfferedIncompatibleQosStatus	total_count	the total number of times the writer encountered a reader requesting a QoS which was was not compatible with the one offered by the writer
		total_count_change	the change in total_count since last being retrieved
		last_policy_id	the last id of the QoSPolicy which was incompatible
		policies	a collection of QoSPolicy ids and the number times they were found to be incompatible
	LivelinessLostStatus	total_count	the total number of times a writer became “dead” by not asserting its liveliness often enough
	LivelinessLostStatus	total_count_change	the change in total_count since last being retrieved
	PublicationMatchedStatus	total_count	the total number of times a writer has encountered a reader it has a “match” with
		total_count_change	the change in total_count since last being retrieved
		current_count	the current number of readers a writer has a “match” with
		current_count_change	the change in current_count since last being retrieved
		last_subscription_handle	handle to the last reader causing this status to change
DataReader	RequestedDeadlineMissedStatus	total_count	total number of missed deadlines for instances read by the reader
		total_count_change	the change in total_count since last being retrieved
		last_instance_handle	the last instance handle to miss a deadline
	RequestedIncompatibleQosStatus	total_count	the total number of times the reader encountered a writer offering a QoS which was was not compatible with the one requested by the reader
		total_count_change	the change in total_count since last being retrieved
		last_policy_id	the last id of the QoSPolicy which was incompatible
		policies	a collection of QoSPolicy ids and the number times they were found to be incompatible
	SampleRejectedStatus	total_count	total number of samples rejected by the reader
		total_count_change	the change in total_count since last being retrieved
		last_reason	the last reason for rejecting a sample
		last_instance_handle	handle to last instance encountering a rejected sample
	LivelinessChangedStatus	alive_count	the total number of matching writers that are alive
		alive_count_change	the change in alive_count since last being retrieved
		not_alive_count	the total number of matching writers that are dead
		not_alive_count_change	the change in not_alive_count since last being retrieved
		last_publication_handle	handle to the last writer causing this to change
	SubscriptionMatchedStatus	total_count	the total number of times a reader has encountered a writer it has a “match” with
		total_count_change	the change in total_count since last being retrieved
		current_count	the current number of writers a reader has a “match” with
		current_count_change	the change in current_count since last being retrieved
		last_publication_handle	handle to the writer causing this status to change
	SampleLostStatus	total_count	the total number of samples lost in the topic
	SampleLostStatus	total_count_change	the change in total_count since last being retrieved

Fields of status objects containing counts of events will have both a cumulative and interval count, where the cumulative count will keep track of all changes during the lifetime of the DDS entity, and the interval count is the number of changes since the previous readout of the status. To access the statuses, use the following functions on the entity:

CycloneDDS-CXX Status accessors¶
CDDS-CXX Entity Type	Status Entity	Accessor
Topic	InconsistentTopicStatus	inconsistent_topic_status
DataWriter	OfferedDeadlineMissedStatus	offered_deadline_missed_status
	OfferedIncompatibleQosStatus	offered_incompatible_qos_status
	LivelinessLostStatus	liveliness_lost_status
	PublicationMatchedStatus	publication_matched_status
DataReader	RequestedDeadlineMissedStatus	requested_deadline_missed_status
	RequestedIncompatibleQosStatus	requested_incompatible_status
	SampleRejectedStatus	sample_rejected_status
	LivelinessChangedStatus	liveliness_changed_status
	SubscriptionMatchedStatus	subscription_matched_status
	SampleLostStatus	sample_lost_status

The following code fragment shows statuses that make a writer wait until readers are present:

dds::pub::DataWriter<DataType> wr(publisher, topic);
while (0 == wr.publication_matched_status().current_count())
        std::this_thread::sleep_for(std::chrono::milliseconds(20));

The writer polls the total number of readers that are receiving data from it at 20 millisecond intervals for as long as there are no readers.