org.omg.dds.core.policy

Interface History

All Superinterfaces:

DDSObject, QosPolicy, QosPolicy.ForDataReader, QosPolicy.ForDataWriter, QosPolicy.ForTopic, Serializable

public interface History
extends QosPolicy.ForTopic, QosPolicy.ForDataReader, QosPolicy.ForDataWriter

Specifies the behavior of the Service in the case where the value of a sample changes (one or more times) before it can be successfully communicated to one or more existing subscribers. This QoS policy controls whether the Service should deliver only the most recent value, attempt to deliver all intermediate values, or do something in between. On the publishing side this policy controls the samples that should be maintained by the DataWriter on behalf of existing DataReader entities. The behavior with regards to a DataReader entities discovered after a sample is written is controlled by the Durability. On the subscribing side it controls the samples that should be maintained until the application "takes" them from the Service via DataReader.take(). Concerns: Topic, DataReader, DataWriter RxO: No Changeable: No

1. This policy controls the behavior of the Service when the value of an instance changes before it is finally communicated to some of its existing DataReader entities.
2. If the kind is set to History.Kind.KEEP_LAST, then the Service will only attempt to keep the latest values of the instance and discard the older ones. In this case, the value of depth regulates the maximum number of values (up to and including the most current one) the Service will maintain and deliver. The default (and most common setting) for depth is one, indicating that only the most recent value should be delivered.
3. If the kind is set to History.Kind.KEEP_ALL, then the Service will attempt to maintain and deliver all the values of the instance to existing subscribers. The resources that the Service can use to keep this history are limited by the settings of the ResourceLimits. If the limit is reached, then the behavior of the Service will depend on the Reliability. If the reliability kind is Reliability.Kind.BEST_EFFORT, then the old values will be discarded. If reliability is Reliability.Kind.RELIABLE, then the Service will block the DataWriter until it can deliver the necessary old values to all subscribers.

The setting of HISTORY depth must be consistent with the RESOURCE_LIMITS maxSamplesPerInstance. For these two QoS to be consistent, they must verify that depth <= maxSamplesPerInstance.

See Also:

Reliability, ResourceLimits

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	History.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
int	getDepth()
History.Kind	getKind()
History	withDepth(int depth) Copy this policy and override the value of the property.
History	withKeepAll()
History	withKeepLast(int depth)
History	withKind(History.Kind kind) Copy this policy and override the value of the property.

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

getEnvironment

Method Detail

getKind

History.Kind getKind()

Returns:

the kind

getDepth

int getDepth()

Returns:

the depth

withKind

History withKind(History.Kind kind)

Copy this policy and override the value of the property.

Returns:

a new policy

withDepth

History withDepth(int depth)

Copy this policy and override the value of the property.

Returns:

a new policy

withKeepAll

History withKeepAll()

Returns:

History with keep-all policy

withKeepLast

History withKeepLast(int depth)

Returns:

History with keep-last policy