<<cert>> Specifies the behavior of RTI Connext DDS Micro when a sample value changes one or more times before it can be successfully communicated to 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.

Detailed Description

<<cert>> Specifies the behavior of RTI Connext DDS Micro when a sample value changes one or more times before it can be successfully communicated to 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 the 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 an instance value changes before it is communicated to its existing DDS_DataReader entities.

When the kind is set to DDS_KEEP_LAST_HISTORY_QOS, RTI Connext DDS Micro will only keep the latest values of the instance and discard older ones. The value of depth regulates the maximum number of values that RTI Connext DDS Micro will maintain and deliver. The default for depth is 1, which means only the most recent value is delivered.

Consistency

The depth setting must be consistent with the RESOURCE_LIMITS max_samples_per_instance setting. This requires the following constraint: depth <= max_samples_per_instance.