7.4. Connext DDS Features

Because RTI Connector is a simplified API, it provides access to a subset of the features in RTI Connext DDS.

In addition to the functionality described in the rest of this documentation, this section summarizes the support that Connector provides for some notable Connext DDS features.

7.4.1. General features

General Features

Feature	Level of support	Notes
Quality of Service (QoS)	Partial	Most QoS policies are supported because they can be configured in XML, but those that are designed to be mutable can’t be changed in Connector. QoS policies that require a supporting API may have limited or no support. A few examples of QoS policies that are fully supported in Connector: Reliability Durability History Ownership A few examples of QoS policies that are supported but can’t be changed in Connector even though they are mutable by design and changeable in other APIs: Partition Lifespan Ownership Strength Property and User Data Time-Based Filter A few examples of QoS policies that have limited support because they require a supporting API that is not available in Connector: Batch - fully supported except that manual flushing is not available Entity Factory - autoenable_created_entities can be set to false only for a subscriber, in order to enable an Input only when Connector.get_input() is called. Property - Properties can be set in XML, but they can’t be looked up in Connector Topic Qos is not supported in Connector. Use DataReader QoS and DataWriter QoS directly.
Entity Statuses	Partial	Only Input.wait() (data available), Input.wait_for_publications(), and Output.wait_for_subscriptions() are supported.
Managing Data Instances	Partial	It is possible to dispose or unregister an instance (see Output.write()), and instances are automatically registered when first written, but on the Input side, the instance status is not currently exposed. Instance handles are not exposed.
Application Acknowledgment	Partial	DDS_APPLICATION_AUTO_ACKNOWLEDGMENT_MODE is supported. If enabled, when a call to Input.take() or Input.read() is followed by another call, the second one automatically acknowledges the samples read in the first one. DDS_APPLICATION_EXPLICIT_ACKNOWLEDGMENT_MODE is not supported.
Request-Reply	Partial	The correlation between two samples can be established at the application level: The Requester application writes by calling Output.write() with the parameter identity=A (the request sample) The Replier application receives the request sample, obtains the identity (A), from “SampleIterator.info and writes a new sample with related_sample_identity=A (the reply sample) The Requester application receives the reply sample, and correlates the related_sample_identity from SampleIterator.info with the identity it used in the first step.
Topic Queries	Partial	Input doesn’t have the API to create a TopicQuery, but in the configuration file a data_writer can enable support for TopicQuery so other Connext DDS Subscribers can query the Connector Publisher.
Zero Copy Transfer Over Shared Memory	Not supported	Only available in C and C++.
Built-in Topics	Not supported	API not available.
Transport Plugins	Partial	The built-in transports can be configured in XML, but add-ons cannot be loaded (see next).
Add-on Libraries (such as Monitoring, Security Plugins )	Not supported	Connector currently cannot load dynamically linked add-on libraries.

7.4.2. Features related to sending data

Features Related to Sending Data

Feature	Level of support	Notes
Waiting for Acknowledgments	Supported	See Output.wait().
Coherent Sets	Not supported	API not available.
Flow Controllers	Partial	Most functionality is available via XML QoS configuration.
Asserting Liveliness Manually	Not supported	API not available.
Collaborative DataWriters	Limited	The virtual GUID can be set per writer in XML, but not per sample.

7.4.3. Features related to receiving data

Features Related to Receiving Data

Feature	Level of support	Notes
Content-Filtered Topics	Partial	Configurable in XML but it can’t be modified after creation
Sample Info	Partial	See SampleIterator.info
Query Conditions	Not supported	API not available
Group-Ordered Access	Not supported	API not available
Waiting for Historical Data	Not supported	API not available

7.4.4. Features related to the type system

Features Related to the Type System

Feature	Level of support	Notes
DDS type system	Supported	Connector can use any DDS type. Types are defined in XML.
Type extensibility	Supported	Connector supports type extensibility, including mutable types in the XML definition of types. It also supports type-consistency enforcement and sample-assignability enforcement; these checks are performed by the RTI Connext DDS Core.
Optional members	Supported	See Accessing optional members.
Default values	Supported	For example, to declare a default value for a member: <struct name= "MyType" extensibility="mutable"> <!-- ... --> <member name="my_int" type="int32" default="20" /> </struct> Now the value for my_int when you call Output.write() without setting it explicitly is 20. And when you receive a data sample in an Input from a Publisher whose type is compatible, but doesn’t have the field my_int, the value you receive will be 20.
Unbounded data	Supported	To declare an unbounded sequence or string, set its max length to -1: <struct name= "MyType"> <member name="my_unbounded_int_sequence" sequenceMaxLength="-1" type="int32"/> <member name="my_bounded_int_sequence" sequenceMaxLength="10" type="int32"/> </struct> For any Output using a topic for a type with unbounded members, set the following in the <property> QoS policy: <datawriter_qos> <!-- ... --> <property> <value> <element> <name> dds.data_writer.history.memory_manager.fast_pool.pool_buffer_max_size </name> <value>4096</value> </element> </value> </property> </datawriter_qos> The value 4096 is a threshold that indicates Connext DDS should allocate memory dynamically for data samples that exceed that size. For samples below that threshold, memory comes from pre-allocated buffers. If the unbounded member is a key, then in any Input that uses the type, set the following: <datareader_qos> <!-- ... --> <property> <value> <element> <name> dds.data_reader.history.memory_manager.fast_pool.pool_buffer_max_size </name> <value>4096</value> </element> </value> </property> <datareader_qos>
FlatData Language Binding	Not supported	However, an Input can receive data published by other Connext DDS applications that use FlatData.