PROPERTY QosPolicy (DDS Extension)

The PROPERTY QosPolicy stores name/value (string) pairs that can be used to configure certain parameters of Connext DDS that are not exposed through formal QoS policies.

It can also be used to store and propagate application-specific name/value pairs that can be retrieved by user code during discovery. This is similar to the USER_DATA QosPolicy, except this policy uses (name, value) pairs, and you can select whether or not a particular pair should be propagated (included in the built-in topic).

It includes the member in DDS_PropertyQosPolicy.

DDS_PropertyQosPolicy

Type	Field Name	Description
DDS_PropertySeq	value	A sequence of: (name, value) pairs and booleans that indicate whether the pair should be propagated (included in the entity’s built-in topic upon discovery).

The Property QoS stores name/value pairs for an Entity. Both the name and value are strings. Certain configurable parameters for Entities that do not have a formal DDS QoS definition may be configured via this QoS by using a pre-defined name and the desired setting in string form.

You can manipulate the sequence of properties (name, value pairs) with the standard methods available for sequences. You can also use the helper class, DDSPropertyQosPolicyHelper, which provides another way to work with a PropertyQosPolicy object.

The PropertyQosPolicy may be used to configure:

• Durable writer history (see How To Configure Durable Writer History)
• Durable reader state (see How To Configure a DataReader for Durable Reader State)
• Built-in and extension Transport Plugins (see Setting Builtin Transport Properties with the PropertyQosPolicy, Setting Up a Transport with the Property QoS, Configuring the TCP Transport).
• Automatic registration of built-in types (see Registering Built-in Types)
• Clock Selection
• Turbo Mode and Automatic Throttling for DataWriter Performance—Experimental Features
• Location or content of your license from RTI (see License Management, in the Getting Started Guide)

In addition, you can add your own name/value pairs to the Property QoS of an Entity. You may also use this QosPolicy to direct Connext DDS to propagate these name/value pairs with the discovery information for the Entity. Applications that discover the Entity can then access the user-specific name/value pairs in the discovery information of the remote Entity. This allows you to add meta-information about an Entity for application-specific use, for example, authentication/authorization certificates (which can also be done using the User or Group Data QoS).

Reasons for using the PropertyQosPolicy include:

• Some features can only be configured through the PropertyQosPolicy, not through other QoS or API.s For example, Durable Reader State, Durable Writer History, Built-in Types, Monotonic Clock.
• Alternative way to configure built-in transports settings. For example, to use non-default values for the built-in transports without using the PropertyQosPolicy, you would have to create a DomainParticipant disabled, change the built-in transport property settings, then enable the DomainParticipant. Using the PropertyQosPolicy to configure built-in transport settings will save you the work of enabling and disabling the DomainParticipant. Also, transport settings are not a QoS and therefore cannot be configured through an XML file. By configuring built-in transport settings through the PropertyQosPolicy instead, XML files can be used.

When using the Java or .NET APIs, transport configuration must take place through the PropertyQosPolicy (not through the transport property structures).

• Alternative way to support multiple instances of built-in transports (without using Transport API).
• Alternative way to dynamically load extension transports (such as RTI Secure WAN Transport1RTI Secure WAN Transport is an optional component that is installed separately. or RTI TCP Transport2RTI TCP Transport is included with your Connext DDS distribution but is not a built-in transport and therefore not enabled by default. ) or user-created transport plugins in C/C++ language bindings. If the extension or user-created transport plugin is installed using the transport API instead, the library that extra transport library/code will need to be linked into your application and may require recompilation.
• Allows full pluggable transport configuration for non-C/C++ language bindings (Java, C++/CLI, C#, etc.) The pluggable transport API is not available in those languages. Without using PropertyQosPolicy, you cannot use extension transports (such as RTI Secure WAN Transport) and you cannot create your own custom transport.
• Alternative way to provide a license for platforms that do not support a file system, or if a default license location is not feasible and environment variables are not supported.

The PropertyQosPolicyHelper operations are described in . For more information, see the API Reference HTML documentation.

PropertyQoSPolicyHelper Operations

Operation	Description
get_number_of_properties	Gets the number of properties in the input policy.
assert_property	Asserts the property identified by name in the input policy. (Either adds it, or replaces an existing one.)
add_property	Adds a new property to the input policy.
assert_pointer_property	Asserts the property identified by name in the input policy. Used when the property to store is a pointer.
add_pointer_property	Adds a new property to the input policy. Used when the property to store is a pointer.
lookup_property	Searches for a property in the input policy given its name.
remove_property	Removes a property from the input policy.
get_properties	Retrieves a list of properties whose names match the input prefix.

Properties

This QosPolicy can be changed at any time.

There is no requirement that the publishing and subscribing sides use compatible values.

Related QosPolicies

• DOMAIN_PARTICIPANT_RESOURCE_LIMITS QosPolicy (DDS Extension)

Applicable Entities

• DataWriters
• DataReaders
• DomainParticipants

System Resource Considerations

The DOMAIN_PARTICIPANT_RESOURCE_LIMITS QosPolicy (DDS Extension) contains several fields for configuring the resources associated with the properties stored in this QosPolicy.

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