org.omg.dds.core.policy

Interface Liveliness

All Superinterfaces:

Comparable<Liveliness>, DDSObject, QosPolicy, QosPolicy.ForDataReader, QosPolicy.ForDataWriter, QosPolicy.ForTopic, RequestedOffered<Liveliness>, Serializable

public interface Liveliness
extends QosPolicy.ForTopic, QosPolicy.ForDataReader, QosPolicy.ForDataWriter, RequestedOffered<Liveliness>

Determines the mechanism and parameters used by the application to determine whether an Entity is "active" (alive). The "liveliness" status of an Entity is used to maintain instance ownership in combination with the setting of the Ownership. The application is also informed via an Entity Status change when an Entity is no longer alive. The DataReader requests that liveliness of the writers is maintained by the requested means and loss of liveliness is detected with delay not to exceed the leaseDuration. The DataWriter commits to signaling its liveliness using the stated means at intervals not to exceed the leaseDuration. The default kind is Liveliness.Kind.AUTOMATIC and the default value of the leaseDuration is infinite. Concerns: Topic, DataReader, DataWriter RxO: Yes Changeable: No This policy has several settings to support both data objects that are updated periodically as well as those that are changed sporadically. It also allows customizing for different application requirements in terms of the kinds of failures that will be detected by the liveliness mechanism. The Liveliness.Kind.AUTOMATIC liveliness setting is most appropriate for applications that only need to detect failures at the process level, but not application-logic failures within a process. The Service takes responsibility for renewing the leases at the required rates and thus, as long as the local process where a DomainParticipant is running and the link connecting it to remote participants remains connected, the entities within the DomainParticipant will be considered alive. This requires the lowest overhead. The MANUAL settings (Liveliness.Kind.MANUAL_BY_PARTICIPANT, Liveliness.Kind.MANUAL_BY_TOPIC) require the application on the publishing side to periodically assert the liveliness before the lease expires to indicate the corresponding Entity is still alive. The action can be explicit by calling the assertLiveliness operations (DataWriter.assertLiveliness(), DomainParticipant.assertLiveliness()) or implicit by writing some data. The two possible manual settings control the granularity at which the application must assert liveliness.

• The setting MANUAL_BY_PARTICIPANT requires only that one Entity within the publisher is asserted to be alive to deduce all other Entity objects within the same DomainParticipant are also alive.
• The setting MANUAL_BY_TOPIC requires that at least one instance within the DataWriter is asserted.

The value offered is considered compatible with the value requested if and only if the following conditions are met:

1. the inequality "offered kind >= requested kind" evaluates to true. For the purposes of this inequality, the values of LIVELINESS kind are considered ordered such that: AUTOMATIC < MANUAL_BY_PARTICIPANT < MANUAL_BY_TOPIC .
2. the inequality "offered leaseDuration <= requested leaseDuration" evaluates to true.

Changes in LIVELINESS must be detected by the Service with a time granularity greater or equal to the leaseDuration. This ensures that the value of the LivelinessChangedStatus is updated at least once during each leaseDuration and the related Listeners and WaitSets are notified within a leaseDuration from the time the LIVELINESS changed.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	Liveliness.Kind

Nested classes/interfaces inherited from interface org.omg.dds.core.policy.QosPolicy

QosPolicy.ForDataReader, QosPolicy.ForDataWriter, QosPolicy.ForDomainParticipant, QosPolicy.ForDomainParticipantFactory, QosPolicy.ForPublisher, QosPolicy.ForSubscriber, QosPolicy.ForTopic

Method Summary

Methods

Modifier and Type	Method and Description
Liveliness.Kind	getKind()
Duration	getLeaseDuration()
Liveliness	withAutomatic()
Liveliness	withKind(Liveliness.Kind kind) Copy this policy and override the value of the property.
Liveliness	withLeaseDuration(Duration leaseDuration) Copy this policy and override the value of the property.
Liveliness	withLeaseDuration(long leaseDuration, TimeUnit unit) Copy this policy and override the value of the property.
Liveliness	withManualByParticipant()
Liveliness	withManualByTopic()

Methods inherited from interface org.omg.dds.core.DDSObject

getEnvironment

Methods inherited from interface org.omg.dds.core.policy.RequestedOffered

requestedOfferedContract

Methods inherited from interface java.lang.Comparable

compareTo

Method Detail

getKind

Liveliness.Kind getKind()

Returns:

the kind

getLeaseDuration

Duration getLeaseDuration()

withKind

Liveliness withKind(Liveliness.Kind kind)

Copy this policy and override the value of the property.

Returns:

a new policy

withLeaseDuration

Liveliness withLeaseDuration(Duration leaseDuration)

Copy this policy and override the value of the property.

Returns:

a new policy

withLeaseDuration

Liveliness withLeaseDuration(long leaseDuration,
                           TimeUnit unit)

Copy this policy and override the value of the property.

Returns:

a new policy

withAutomatic

Liveliness withAutomatic()

withManualByParticipant

Liveliness withManualByParticipant()

withManualByTopic

Liveliness withManualByTopic()