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QoS Policies

Quality of Service (QoS) policies. More...


 QoS Policy Traits
 The traits types policy_id and policy_name provide information about a QoS policy.
 <<extension>> Specifies the asynchronous publishing settings of the dds::pub::Publisher instances.
 <<extension>> Configures the availability of data.
 <<extension>> Batch QoS policy used to enable batching in dds::pub::DataWriter instances.
 <<extension>> Various threads and resource limits settings used by RTI Connext to control its internal database.
 <<extension>> Specifies the DataReader-specific protocol QoS.
 <<extension>> Various settings that configure how DataReaders allocate and use physical memory for internal resources.
 <<extension>> Along with rti::core::policy::WireProtocol and rti::core::policy::DataReaderProtocol, this QoS policy configures the DDS on-the-network protocol (RTPS).
 <<extension>> Various settings that configure how a dds::pub::DataWriter allocates and uses physical memory for internal resources.
 Expresses the maximum duration (deadline) within which an instance is expected to be updated.
 Controls the criteria used to determine the logical order among changes made by dds::pub::Publisher entities to the same instance of data (i.e., matching dds::topic::Topic and key).
 <<extension>> Specifies the attributes required to discover participants in the domain.
 <<extension>> Specifies the discovery configuration QoS.
 <<extension>> Various settings that configure how a dds::domain::DomainParticipant allocates and uses physical memory for internal resources, including the maximum sizes of various properties.
 This QoS policy specifies whether or not RTI Connext will store and deliver previously published data samples to new dds::sub::DataReader entities that join the network later.
 Various settings to configure the external RTI Persistence Service used by RTI Connext for DataWriters with a dds::core::policy::Durability setting of dds::core::policy::DurabilityKind::PERSISTENT or dds::core::policy::DurabilityKind::TRANSIENT.
 A QoS policy for all dds::core::Entity types that can act as factories for one or more other dds::core::Entity types.
 <<extension>> Assigns a name to a dds::domain::DomainParticipant, dds::pub::Publisher, dds::sub::Subscriber, dds::pub::DataWriter or dds::sub::DataReader. Except for dds::pub::Publisher and dds::sub::Subscriber, these names are visible during the discovery process and in RTI tools to help you visualize and debug your system.
 <<extension>> Configures the internal thread in a DomainParticipant that handles timed events.
 <<extension>> Configures multi-thread concurrency and deadlock prevention capabilities.
 Specifies the behavior of RTI Connext in the case where the value of an instance changes (one or more times) before it can be successfully communicated to one or more existing subscribers.
 Attaches a buffer of opaque data that is distributed by means of Built-in Topics during discovery.
 Provides a hint as to the maximum acceptable delay from the time the data is written to the time it is received by the subscribing applications.
 Specifies how long the data written by the dds::pub::DataWriter is considered valid.
 Specifies and configures the mechanism that allows dds::sub::DataReader entities to detect when dds::pub::DataWriter entities become disconnected or "dead.".
 <<extension>> The QoS policy used to report the configuration of a MultiChannel DataWriter as part of dds::topic::PublicationBuiltinTopicData.
 <<extension>> Configures the RTI Connext logging facility.
 <<extension>> Configures the ability of a DataWriter to send data on different multicast groups (addresses) based on the value of the data.
 Specifies whether it is allowed for multiple dds::pub::DataWriter (s) to write the same instance of the data and if so, how these modifications should be arbitrated.
 Specifies the value of the strength used to arbitrate among multiple dds::pub::DataWriter objects that attempt to modify the same instance of a data type (identified by dds::topic::Topic + key).
 Set of strings that introduces a logical partition among the topics visible by a dds::pub::Publisher and a dds::sub::Subscriber.
 Specifies how the samples representing changes to data instances are presented to a subscribing application.
 <<extension>> Configures the way that XML documents containing QoS profiles are loaded by RTI Connext.
 <<extension>> Stores name/value (string) pairs that can be used to configure certain parameters of RTI Connext that are not exposed through formal QoS policies. Can also be used to store and propagate application-specific name/value pairs that can be retrieved by user code during discovery.
 <<extension>> Specifies how RTI Connext sends application data on the network. This QoS policy can be used to tell RTI Connext to use its own thread to send data, instead of the user thread.
 Controls how a DataReader manages the lifecycle of the data that it has received.
 <<extension>> Configures threads used by RTI Connext to receive and process data from transports (for example, UDP sockets).
 Indicates the level of reliability offered/requested by RTI Connext.
 Controls the amount of physical memory allocated for DDS entities, if dynamic allocations are allowed, and how they occur. Also controls memory usage among different instance values for keyed topics.
 <<extension>> Service QoS policy is used to indicate what kind of service is associated with the DDS entity.
 <<extension>> Configures DomainParticipant-independent resources used by RTI Connext.
 Filter that allows a dds::sub::DataReader to specify that it is interested only in (potentially) a subset of the values of the data.
 Attaches a buffer of opaque data that is distributed by means of Built-in Topics during discovery.
 Configures the ability of a dds::pub::DataWriter to publish historical samples.
 <<extension>> Specifies which built-in transports are used.
 <<extension>> Specifies the multicast address on which a dds::sub::DataReader wants to receive its data. It can also specify a port number, as well as a subset of the available (at the dds::domain::DomainParticipant level) transports with which to receive the multicast data.
 <<extension>> Specifies a list of topic expressions and addresses that can be used by an Entity with a specific topic name to receive data.
 This QoS policy allows the application to take advantage of transport that are capable of sending messages with different priorities.
 <<extension>> Specifies the physical transports that a dds::pub::DataWriter or dds::sub::DataReader may use to send or receive data.
 <<extension>> Specifies a subset of transports and a port number that can be used by an Entity to receive data.
 Defines the rules for determining whether the type used to publish a given topic is consistent with that used to subscribe to it.
 <<extension>> Allows you to attach application-specific values to a dds::pub::DataWriter or dds::sub::DataReader, which are passed to the serialization or deserialization routine of the associated data type and choose whether to set padding bytes to zero during serialization.
 Attaches a buffer of opaque data that is distributed by means of Built-in Topics during discovery.
 Controls how a DataWriter handles the lifecycle of the instances (keys) that it is registered to manage.
 <<extension>> Specifies the wire protocol related attributes for the dds::domain::DomainParticipant.


class  dds::core::policy::QosPolicyCount
 <<value-type>> Holds a counter for a QosPolicyId More...


typedef std::vector
< QosPolicyCount > 
 A vector of QosPolicyCount.
typedef uint32_t dds::core::policy::QosPolicyId
 Identifies a Qos policy.

Detailed Description

Quality of Service (QoS) policies.

Data Distribution Service (DDS) relies on the use of QoS. A QoS is a set of characteristics that controls some aspect of the behavior of DDS. A QoS is comprised of individual QoS policies (objects conceptually deriving from an abstract QosPolicy class).

Supported QoS policies

The QosPolicy provides the basic mechanism for an application to specify quality of service parameters. It has an attribute name that is used to uniquely identify each QosPolicy.

QosPolicy implementation is comprised of a name, an ID, and a type. The type of a QosPolicy value may be atomic, such as an integer or float, or compound (a structure). Compound types are used whenever multiple parameters must be set coherently to define a consistent value for a QosPolicy.

QoS (i.e., a list of QosPolicy objects) may be associated with all dds::core::Entity objects in the system such as dds::topic::Topic, dds::pub::DataWriter, dds::sub::DataReader, dds::pub::Publisher, dds::sub::Subscriber, and dds::domain::DomainParticipant.

Specifying QoS on entities

QosPolicies can be set programmatically when an dds::core::Entity is created, or modified with the dds::core::Entity's set_qos (abstract) method.

QosPolicies can also be configured from XML resources (files, strings). With this approach, you can change the QoS without recompiling the application. For more information, see Configuring QoS Profiles with XML.

To customize a dds::core::Entity's QoS before creating the entity, the correct pattern is:

Each QosPolicy is treated independently from the others. This approach has the advantage of being very extensible. However, there may be cases where several policies are in conflict. Consistency checking is performed each time the policies are modified via the set_qos (abstract) operation, or when the dds::core::Entity is created.

When a policy is changed after being set to a given value, it is not required that the new value be applied instantaneously; RTI Connext is allowed to apply it after a transition phase. In addition, some QosPolicy have immutable semantics, meaning that they can only be specified either at dds::core::Entity creation time or else prior to calling the dds::core::Entity::enable operation on the entity.

Each dds::core::Entity can be configured with a list of QosPolicy objects. However, not all QosPolicies are supported by each dds::core::Entity. For instance, a dds::domain::DomainParticipant supports a different set of QosPolicies than a dds::topic::Topic or a dds::pub::Publisher.

QoS compatibility

In several cases, for communications to occur properly (or efficiently), a QosPolicy on the publisher side must be compatible with a corresponding policy on the subscriber side. For example, if a dds::sub::Subscriber requests to receive data reliably while the corresponding dds::pub::Publisher defines a best-effort policy, communication will not happen as requested.

To address this issue and maintain the desirable decoupling of publication and subscription as much as possible, the QosPolicy specification follows the subscriber-requested, publisher-offered pattern.

In this pattern, the subscriber side can specify a "requested" value for a particular QosPolicy. The publisher side specifes an "offered" value for that QosPolicy. RTI Connext will then determine whether the value requested by the subscriber side is compatible with what is offered by the publisher side. If the two policies are compatible, then communication will be established. If the two policies are not compatible, RTI Connext will not establish communications between the two dds::core::Entity objects and will record this fact by means of the dds::core::status::StatusMask::offered_incompatible_qos() on the publisher end and dds::core::status::StatusMask::requested_incompatible_qos() on the subscriber end. The application can detect this fact by means of a Listener or a dds::core::cond::Condition.

The following properties are defined on a QosPolicy.

Typedef Documentation

typedef std::vector<QosPolicyCount> dds::core::policy::QosPolicyCountSeq

A vector of QosPolicyCount.

Identifies a Qos policy.

RTI Connext Modern C++ API Version 5.3.1 Copyright © Mon Feb 19 2018 Real-Time Innovations, Inc