qualityOfService QML Value Type

ROS 2 Quality of Service settings for a publisher or subscriber. More...

Import Statement:	`import QtRos2.Core`
Status:	Experimental Extension

Properties

durability : enumeration
history : enumeration
liveliness : enumeration
queueSize : int
reliability : enumeration

Detailed Description

Holds the QoS policies (reliability, durability, history, liveliness and the queueSize / depth) applied to an Entity's qos property. Policy values are the enums on QualityOfService, e.g.

SomeSubscriber {
    qos.reliability: QualityOfService.ReliabilityBestEffort
    qos.durability: QualityOfService.DurabilityTransientLocal
    qos.queueSize: 5
}

For common cases prefer a ready-made profile from QualityOfService: qos: QualityOfService.sensorData().

Note: This is unrelated to qoSProfile from QtRos2.RosgraphMsgs, which is the rosgraph_msgs/QoSProfile introspection message.

See also QualityOfService.

Property Documentation

durability : enumeration

Whether the middleware keeps samples for subscribers that join late.

Constant	Description
`QualityOfService.DurabilitySystemDefault`	Leave the policy to the RMW implementation. This is the default.
`QualityOfService.DurabilityVolatile`	Deliver only to subscribers that are already connected.
`QualityOfService.DurabilityTransientLocal`	Keep the last `queueSize` samples so a late subscriber still receives them: how latched topics such as `/tf_static` work.
`QualityOfService.DurabilityBestAvailable`	Request the strongest policy that still matches every endpoint discovered so far.

history : enumeration

How many samples the middleware buffers.

Constant	Description
`QualityOfService.HistorySystemDefault`	Leave the policy to the RMW implementation. This is the default.
`QualityOfService.HistoryKeepLast`	Buffer at most `queueSize` samples, discarding the oldest.
`QualityOfService.HistoryKeepAll`	Buffer every sample, up to the middleware's resource limits. `queueSize` is ignored.

liveliness : enumeration

How an endpoint reports that it is still alive. A publisher and a subscriber match only if the publisher's policy is at least as strict as the subscriber's, ordered Automatic, then ManualByTopic.

Constant	Description
`QualityOfService.LivelinessSystemDefault`	Leave the policy to the RMW implementation. This is the default.
`QualityOfService.LivelinessAutomatic`	The middleware asserts liveliness on the application's behalf for as long as the process is running.
`QualityOfService.LivelinessManualByTopic`	The publisher asserts its own liveliness per topic. Note that this module exposes no lease duration and no way to assert liveliness, so in practice this only affects which endpoints match.
`QualityOfService.LivelinessBestAvailable`	Request the strongest policy that still matches every endpoint discovered so far. Note: ROS 2 also had a `MANUAL_BY_NODE` policy. It is deliberately not exposed here: rmw deprecated it in Jazzy and removed it in Kilted. Use `LivelinessManualByTopic`, which matches anything `MANUAL_BY_NODE` would have matched.

queueSize : int

The depth of the message queue, used when history is QualityOfService.HistoryKeepLast. The default is 10.

reliability : enumeration

How hard the middleware works to deliver every sample.

Constant	Description
`QualityOfService.ReliabilitySystemDefault`	Leave the policy to the RMW implementation. This is the default.
`QualityOfService.ReliabilityReliable`	Retransmit until every sample has been acknowledged.
`QualityOfService.ReliabilityBestEffort`	Send once and drop samples under load: the right choice for high-rate sensor streams where the newest sample matters most.
`QualityOfService.ReliabilityBestAvailable`	Request the strongest policy that still matches every endpoint discovered so far.

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