Configures the ability of a com.rti.dds.publication.DataWriter to publish samples in response to a com.rti.dds.subscription.TopicQuery. More...

Inheritance diagram for TopicQueryDispatchQosPolicy:

Public Attributes
boolean	enable = false
	Allows this writer to dispatch TopicQueries. More...

int	samples_per_period = ResourceLimitsQosPolicy.LENGTH_UNLIMITED
	Sets the maximum number of samples to publish in each publication_period. More...

final Duration_t	publication_period = new Duration_t(1, 0)
	Sets the periodic interval at which samples are published. More...

Public Attributes inherited from QosPolicy
final QosPolicyId_t	id
	The ID of this QoS policy. More...

final String	policy_name
	The name of this QoS policy. More...

Detailed Description

Configures the ability of a com.rti.dds.publication.DataWriter to publish samples in response to a com.rti.dds.subscription.TopicQuery.

Enables the ability of a com.rti.dds.publication.DataWriter to publish historical samples upon reception of a com.rti.dds.subscription.TopicQuery and how often they are published.

Since a TopicQuery selects previously written samples, the DataWriter must have a com.rti.dds.infrastructure.DurabilityQosPolicy.kind different from com.rti.dds.infrastructure.DurabilityQosPolicyKind.DurabilityQosPolicyKind.VOLATILE_DURABILITY_QOS. Also, com.rti.dds.infrastructure.ReliabilityQosPolicy.kind must be set to com.rti.dds.infrastructure.ReliabilityQosPolicyKind.RELIABLE_RELIABILITY_QOS.

Only samples that fall within the com.rti.dds.infrastructure.DurabilityQosPolicy.writer_depth for an instance are evaluated against the TopicQuery filter. While the DataWriter is waiting for acknowledgements from one or more DataReaders, there may temporarily be more than com.rti.dds.infrastructure.DurabilityQosPolicy.writer_depth samples per instance in the DataWriter's queue if the com.rti.dds.infrastructure.HistoryQosPolicy.depth is set to a higher value than com.rti.dds.infrastructure.DurabilityQosPolicy.writer_depth. Those additional samples past com.rti.dds.infrastructure.DurabilityQosPolicy.writer_depth are not eligible to be sent in response to the TopicQuery.

A TopicQuery may select multiple samples at once. The writer will publish them periodically, independently from newly written samples. com.rti.dds.infrastructure.TopicQueryDispatchQosPolicy.publication_period configures the frequency of that period and com.rti.dds.infrastructure.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 com.rti.ndds.example.FooDataWriter.write for the conditions that may cause the write operation to block.)

All the DataWriters that belong to a single com.rti.dds.publication.Publisher and enable TopicQueries share the same event thread, but each DataWriter schedules separate events. To configure that thread, see com.rti.dds.infrastructure.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.