18.1.4.4. InstanceStateKind

enum eprosima::fastdds::dds::InstanceStateKind

Indicates if the samples are from an alive DataWriter or not.

For each instance, the middleware internally maintains an instance state. The instance state can be:

• ALIVE_INSTANCE_STATE indicates that (a) samples have been received for the instance, (b) there are alive DataWriter entities writing the instance, and (c) the instance has not been explicitly disposed (or else more samples have been received after it was disposed).

• NOT_ALIVE_DISPOSED_INSTANCE_STATE indicates the instance was explicitly disposed by a DataWriter by means of the dispose operation.

• NOT_ALIVE_NO_WRITERS_INSTANCE_STATE indicates the instance has been declared as not-alive by the DataReader because it detected that there are no alive DataWriter entities writing that instance.

The precise behavior events that cause the instance state to change depends on the setting of the OWNERSHIP QoS:

• If OWNERSHIP is set to EXCLUSIVE_OWNERSHIP_QOS, then the instance state becomes NOT_ALIVE_DISPOSED_INSTANCE_STATE only if the DataWriter that “owns” the instance explicitly disposes it. The instance state becomes ALIVE_INSTANCE_STATE again only if the DataWriter that owns the instance writes it.

• If OWNERSHIP is set to SHARED_OWNERSHIP_QOS, then the instance state becomes NOT_ALIVE_DISPOSED_INSTANCE_STATE if any DataWriter explicitly disposes the instance. The instance state becomes ALIVE_INSTANCE_STATE as soon as any DataWriter writes the instance again.

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

Values:

enumerator ALIVE_INSTANCE_STATE

Instance is currently in existence.

enumerator NOT_ALIVE_DISPOSED_INSTANCE_STATE

Not alive disposed instance. The instance has been disposed by a DataWriter.

enumerator NOT_ALIVE_NO_WRITERS_INSTANCE_STATE

Not alive no writers for instance. None of the DataWriter objects that are currently alive (according to the LIVELINESS QoS) are writing the instance.