Configures the ability of a DDSDataWriter to publish samples in response to a DDSTopicQuery. More...

Public Attributes
DDS_Boolean	enable
	Allows this writer to dispatch TopicQueries. More...

struct DDS_Duration_t	publication_period
	Sets the periodic interval at which samples are published. More...

DDS_Long	samples_per_period
	Sets the maximum number of samples to publish in each publication_period. More...

Detailed Description

Configures the ability of a DDSDataWriter to publish samples in response to a DDSTopicQuery.

Enables the ability of a DDSDataWriter to publish historical samples upon reception of a DDSTopicQuery and how often they are published.

Since a TopicQuery selects previously written samples, the DataWriter must have a DDS_DurabilityQosPolicy::kind different from DDS_VOLATILE_DURABILITY_QOS. Also, DDS_ReliabilityQosPolicy::kind must be set to DDS_RELIABLE_RELIABILITY_QOS.

A TopicQuery may select multiple samples at once. The writer will publish them periodically, independently from newly written samples. DDS_TopicQueryDispatchQosPolicy::publication_period configures the frequency of that period and DDS_TopicQueryDispatchQosPolicy::samples_per_period configures the maximum number of samples to publish each period.

If the DataWriter blocks during the publication of one of these samples, it will stop and try again the next period. (See FooDataWriter::write for the conditions that may cause the write operation to block.)

All the DataWriters that belong to a single DDSPublisher and enable TopicQueries share the same event thread, but each DataWriter schedules separate events. To configure that thread, see DDS_AsynchronousPublisherQosPolicy::topic_query_publication_thread.

If the DataWriter is dispatching more than one TopicQuery at the same time, the configuration of this periodic event applies to all of them. For example, if a DataWriter receives two TopicQueries around the same time, the period is 1 second, the number of samples per period is 10, the first TopicQuery selects 5 samples, and the second one selects 8, the DataWriter will immediately attempt to publish all 5 for the first TopicQuery and 5 for the second one. After one second, it will publish the remaining 3 samples.