Struct HistoryKind_def

Struct Documentation

struct HistoryKind_def

Public Types

enum Type

Values:

enumerator KEEP_LAST: The Data Distribution Service will only attempt to keep the latest values of the instance and discard the older ones. The attribute “depth” determines how many samples in history will be stored. In other words, only the most recent samples in history are stored. On the publishing side, the Data Distribution Service will only keep the most recent “depth” samples of each instance of data (identified by its key) managed by the DataWriter. On the subscribing side, the DataReader will only keep the most recent “depth” samples received for each instance (identified by its key) until the application “takes” them via the DataReader::take operation. KEEP_LAST_HISTORY_QOS - is the default kind. The default value of depth is 1, indicating that only the most recent value should be delivered. If a depth other than 1 is specified, it should be compatible with the settings of the ResourcelimitsQosPolicy max_samples_per_instance. For these two QosPolicy settings to be compatible, they must verify that depth <= max_samples_per_instance, otherwise a RETCODE_INCONSISTENT_POLICY is generated on relevant operations.

enumerator KEEP_ALL: All samples are stored, provided, the resources are available. On the publishing side, the Data Distribution Service will attempt to keep all samples (representing each value written) of each instance of data (identified by its key) managed by the DataWriter until they can be delivered to all subscribers. On the subscribing side, the Data Distribution Service will attempt to keep all samples of each instance of data (identified by its key) managed by the DataReader. These samples are kept until the application “takes” them from the Data Distribution Service via the DataReader::take operation. The setting of depth has no effect. Its implied value is LENGTH_UNLIMITED. The resources that the Data Distribution Service can use to keep this history are limited by the settings of the ResourceLimitsQosPolicy. If the limit is reached, the behaviour of the Data Distribution Service will depend on the ReliabilityQosPolicy. If the ReliabilityQosPolicy is BEST_EFFORT_RELIABILITY_QOS, the old values are discarded. If ReliabilityQosPolicy is RELIABLE_RELIABILITY_QOS, the Data Distribution Service will block the DataWriter until it can deliver the necessary old values to all subscribers.