RTI Connext C++ API
Version 5.1.0
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Configures the availability of data. More...
Public Attributes | |
DDS_Boolean | enable_required_subscriptions |
Enables support for required subscriptions in a DDSDataWriter. | |
struct DDS_Duration_t | max_data_availability_waiting_time |
Defines how much time to wait before delivering a sample to the application without having received some of the previous samples. | |
struct DDS_Duration_t | max_endpoint_availability_waiting_time |
Defines how much time to wait to discover DataWriters providing samples for the same data source (virtual GUID). | |
struct DDS_EndpointGroupSeq | required_matched_endpoint_groups |
A sequence of endpoint groups. | |
Configures the availability of data.
This QoS policy is used in the context of two features:
Collaborative DataWriters
The Collaborative DataWriters feature allows having multiple DataWriters publishing samples from a common logical data source. The DataReaders will combine the samples coming from the DataWriters in order to reconstruct the correct order at the source.
This QoS policy allows you to configure the ordering and combination process in the DataReader and can be used to support two different use cases:
Each sample published in a DDS domain for a given logical data source is uniquely identified by a pair (virtual GUID, virtual sequence number). Samples from the same data source (same virtual GUID) can be published by different DataWriters. A DataReader will deliver a sample (VGUIDn, VSNm) to the application if one of the following conditions is satisfied:
A DataWriter announces potential availability of samples by using virtual heartbeats (HBs).
When DDS_PresentationQosPolicy::access_scope is set to DDS_TOPIC_PRESENTATION_QOS or DDS_INSTANCE_PRESENTATION_QOS, the virtual HB contains information about the samples contained in the DDSDataWriter history.
When DDS_PresentationQosPolicy::access_scope is set to DDS_GROUP_PRESENTATION_QOS, the virtual HB contains information about all DataWriters in the DDSPublisher.
The frequency at which virtual HBs are sent is controlled by the protocol parameters DDS_RtpsReliableWriterProtocol_t::virtual_heartbeat_period and DDS_RtpsReliableWriterProtocol_t::samples_per_virtual_heartbeat.
Required Subscriptions
In the context of Required Subscriptions, this QoS policy can be used to configure a set of Required Subscriptions on a DDSDataWriter.
Required subscriptions are preconfigured, named subscriptions that may leave and subsequently rejoin the network from time to time, at the same or different physical locations. Any time a required subscription is disconnected, any samples that would have been delivered to it are stored for delivery if and when the subscription rejoins the network.
For a DataWriter, the setting of AVAILABILITY must be set consistenly with that of the RELIABILITY and DURABILITY.
If DDS_AvailabilityQosPolicy::enable_required_subscriptions is set to DDS_BOOLEAN_TRUE, DDS_ReliabilityQosPolicy::kind must be set to DDS_RELIABLE_RELIABILITY_QOS and DDS_DurabilityQosPolicy must be set to a value different than DDS_VOLATILE_DURABILITY_QOS.
DDS_Boolean DDS_AvailabilityQosPolicy::enable_required_subscriptions |
Enables support for required subscriptions in a DDSDataWriter.
[default] DDS_BOOLEAN_FALSE
struct DDS_Duration_t DDS_AvailabilityQosPolicy::max_data_availability_waiting_time |
Defines how much time to wait before delivering a sample to the application without having received some of the previous samples.
Collaborative DataWriters
A sample identified by (VGUIDn, VSNm) will be delivered to the application if this timeout expires for the sample and the following two conditions are satisfied:
Required Subscriptions
This field is not applicable to Required Subscriptions.
[default] DDS_DURATION_AUTO (DDS_DURATION_INFINITE for DDS_GROUP_PRESENTATION_QOS. Otherwise, 0 seconds)
[range] [0, DDS_DURATION_INFINITE], DDS_DURATION_AUTO
struct DDS_Duration_t DDS_AvailabilityQosPolicy::max_endpoint_availability_waiting_time |
Defines how much time to wait to discover DataWriters providing samples for the same data source (virtual GUID).
Collaborative DataWriters
The set of endpoint groups that are required to provide samples for a data source can be configured using required_matched_endpoint_groups.
A non-consecutive sample identified by (VGUIDn, VSNm) cannot be delivered to the application unless DataWriters for all the endpoint groups in required_matched_endpoint_groups are discovered or this timeout expires.
Required Subscriptions
This field is not applicable to Required Subscriptions.
[default] DDS_DURATION_AUTO (DDS_DURATION_INFINITE for DDS_GROUP_PRESENTATION_QOS. Otherwise, 0 seconds)
[range] [0, DDS_DURATION_INFINITE], DDS_DURATION_AUTO
struct DDS_EndpointGroupSeq DDS_AvailabilityQosPolicy::required_matched_endpoint_groups |
A sequence of endpoint groups.
Collaborative DataWriters
In the context of Collaborative DataWriters, it specifies the set of endpoint groups that are expected to provide samples for the same data source.
The quorum count in a group represents the number of DataWriters that must be discovered for that group before the DataReader is allowed to provide non consecutive samples to the application.
A DataWriter becomes a member of an endpoint group by configuring the role_name in DDS_DataWriterQos::publication_name.
Required Subscriptions
In the context of Required Subscriptions, it specifies the set of Required Subscriptions on a DDSDataWriter.
Each Required Subscription is specified by a name and a quorum count.
The quorum count represents the number of DataReaders that have to acknowledge the sample before it can be considered fully acknowledged for that Required Subscription.
A DataReader is associated with a Required Subscription by configuring the role_name in DDS_DataReaderQos::subscription_name.
[default] Empty sequence