DDS::ViewStateKind Struct Reference

Indicates whether or not an instance is new. More...

#include <managed_subscription.h>

Properties
static ViewStateKind	NEW_VIEW_STATE [get]
	New instance. This latest generation of the instance has not previously been accessed. More...
static ViewStateKind	NOT_NEW_VIEW_STATE [get]
	Not a new instance. This latest generation of the instance has previously been accessed. More...
static ViewStateKind	ANY_VIEW_STATE [get]
	Any view state DDS::ViewStateKind::NEW_VIEW_STATE | DDS::ViewStateKind::NOT_NEW_VIEW_STATE. More...

Detailed Description

Indicates whether or not an instance is new.

For each instance (identified by the key), the middleware internally maintains a view state relative to each DDS::DataReader. The view state can be either:

• DDS::ViewStateKind::NEW_VIEW_STATE indicates that either this is the first time that the DDS::DataReader has ever accessed samples of that instance, or else that the DDS::DataReader has accessed previous samples of the instance, but the instance has since been reborn (i.e. become not-alive and then alive again). These two cases are distinguished by examining the DDS::SampleInfo::disposed_generation_count and the DDS::SampleInfo::no_writers_generation_count.

• DDS::ViewStateKind::NOT_NEW_VIEW_STATE indicates that the DDS::DataReader has already accessed samples of the same instance and that the instance has not been reborn since.

The view_state available in the DDS::SampleInfo is a snapshot of the view state of the instance relative to the DDS::DataReader used to access the samples at the time the collection was obtained (i.e. at the time read or take was called). The view_state is therefore the same for all samples in the returned collection that refer to the same instance.

Once an instance has been detected as not having any "live" writers and all the samples associated with the instance are "taken" from the DDS::DataReader, the middleware can reclaim all local resources regarding the instance. Future samples will be treated as "never seen."

Property Documentation

NEW_VIEW_STATE

ViewStateKind DDS::ViewStateKind::NEW_VIEW_STATE

staticget

New instance. This latest generation of the instance has not previously been accessed.

NOT_NEW_VIEW_STATE

ViewStateKind DDS::ViewStateKind::NOT_NEW_VIEW_STATE

staticget

Not a new instance. This latest generation of the instance has previously been accessed.