DDS_HistoryQosPolicy Struct Reference

<<cert>> Specifies the behavior of RTI Connext DDS Micro 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. More...

#include <dds_c_infrastructure.h>

Data Fields
DDS_HistoryQosPolicyKind	kind
	Specifies the kind of history to be kept.
DDS_Long	depth
	Specifies the number of samples to be kept, when the kind is DDS_KEEP_LAST_HISTORY_QOS.

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Detailed Description

<<cert>> Specifies the behavior of RTI Connext DDS Micro 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 QosPolicy controls whether RTI Connext DDS Micro 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 DDS_DataWriter on behalf of existing DDS_DataReader entities.

On the subscribing side it controls the samples that should be maintained until the application "takes" them from RTI Connext DDS Micro.

RTI Connext DDS Micro supports DDS_KEEP_LAST_HISTORY_QOS kind.

Entity:

DDS_Topic, DDS_DataReader, DDS_DataWriter

Properties:

RxO = NO
Changeable = NO

See also:

DDS_ReliabilityQosPolicy

DDS_HistoryQosPolicy

Usage

This policy controls the behavior of RTI Connext DDS Micro when the value of an instance changes before it is finally communicated to some of its existing DDS_DataReader entities.

For kind set to DDS_KEEP_LAST_HISTORY_QOS, RTI Connext DDS Micro 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) RTI Connext DDS Micro will maintain and deliver. The default (and most common setting) for depth is 1, indicating that only the most recent value should be delivered.

Consistency

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

See also:

DDS_ResourceLimitsQosPolicy

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Field Documentation

DDS_HistoryQosPolicyKind DDS_HistoryQosPolicy::kind

Specifies the kind of history to be kept.

[default] DDS_KEEP_LAST_HISTORY_QOS

DDS_Long DDS_HistoryQosPolicy::depth

Specifies the number of samples to be kept, when the kind is DDS_KEEP_LAST_HISTORY_QOS.

If a value other than 1 (the default) is specified, it should be consistent with the settings of the RESOURCE_LIMITS policy. That is:

depth <= DDS_ResourceLimitsQosPolicy::max_samples_per_instance

[default] 1

[range] [1,2147483647]