View States
[Data Samples]

DDS_ViewStateKind and associated elements More...

Typedefs
typedef DDS_UnsignedLong	DDS_ViewStateMask
	A bit-mask (list) of view states, i.e. DDS_ViewStateKind.
Enumerations
enum	DDS_ViewStateKind {   DDS_NEW_VIEW_STATE = 0x0001 << 0,   DDS_NOT_NEW_VIEW_STATE = 0x0001 << 1 }
	Indicates whether or not an instance is new. More...
Variables
const DDS_ViewStateMask	DDS_ANY_VIEW_STATE
	Any view state DDS_NEW_VIEW_STATE | DDS_NOT_NEW_VIEW_STATE.

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Detailed Description

DDS_ViewStateKind and associated elements

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Typedef Documentation

typedef DDS_UnsignedLong DDS_ViewStateMask

A bit-mask (list) of view states, i.e. DDS_ViewStateKind.

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Enumeration Type Documentation

enum DDS_ViewStateKind

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 DDSDataReader. The view state can be either:

• DDS_NEW_VIEW_STATE indicates that either this is the first time that the DDSDataReader has ever accessed samples of that instance, or else that the DDSDataReader 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_NOT_NEW_VIEW_STATE indicates that the DDSDataReader 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 DDSDataReader 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 DDSDataReader, the middleware can reclaim all local resources regarding the instance. Future samples will be treated as "never seen."

Enumerator:

DDS_NEW_VIEW_STATE	New instance. This latest generation of the instance has not previously been accessed.
DDS_NOT_NEW_VIEW_STATE	Not a new instance. This latest generation of the instance has previously been accessed.

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Variable Documentation

const DDS_ViewStateMask DDS_ANY_VIEW_STATE

Any view state DDS_NEW_VIEW_STATE | DDS_NOT_NEW_VIEW_STATE.

Examples:

HelloWorld_subscriber.cxx.