DDS_ReaderDataLifecycleQosPolicy Struct Reference

Controls how a DataReader manages the lifecycle of the data that it has received. More...

Data Fields
struct DDS_Duration_t	autopurge_nowriter_samples_delay
	Minimum duration for which the DDS_DataReader will maintain information regarding an instance once its instance_state becomes DDS_NOT_ALIVE_NO_WRITERS_INSTANCE_STATE.
struct DDS_Duration_t	autopurge_disposed_samples_delay
	Minimum duration for which the DDS_DataReader will maintain samples for an instance once its instance_state becomes DDS_NOT_ALIVE_DISPOSED_INSTANCE_STATE.
struct DDS_Duration_t	autopurge_disposed_instances_delay
	<<extension>> Minimum duration for which the DDS_DataReader will maintain information about a received instance once its instance_state becomes DDS_NOT_ALIVE_DISPOSED_INSTANCE_STATE.

Detailed Description

Controls how a DataReader manages the lifecycle of the data that it has received.

When a DataReader receives data, it is stored in a receive queue for the DataReader. The user application may either take the data from the queue or leave it there.

This QoS policy controls whether or not RTI Connext will automatically remove data from the receive queue (so that user applications cannot access it afterwards) when it detects that there are no more DataWriters alive for that data. It specifies how long a DDS_DataReader must retain information regarding instances that have the instance_state DDS_NOT_ALIVE_NO_WRITERS_INSTANCE_STATE.

Note: This policy is not concerned with keeping reliable reader state or discovery information.

The DDS_DataReader internally maintains the samples that have not been "taken" by the application, subject to the constraints imposed by other QoS policies such as DDS_HistoryQosPolicy and DDS_ResourceLimitsQosPolicy.

The DDS_DataReader also maintains information regarding the identity, view_state and instance_state of data instances even after all samples have been taken. This is needed to properly compute the states when future samples arrive.

Under normal circumstances the DDS_DataReader can only reclaim all resources for instances for which there are no writers and for which all samples have been 'taken'. The last sample the DDS_DataReader will have taken for that instance will have an instance_state of either DDS_NOT_ALIVE_NO_WRITERS_INSTANCE_STATE or DDS_NOT_ALIVE_DISPOSED_INSTANCE_STATE depending on whether or not the last writer that had ownership of the instance disposed it.

In the absence of READER_DATA_LIFECYCLE, this behavior could cause problems if the application forgets to take those samples. "Untaken" samples will prevent the DDS_DataReader from reclaiming the resources and they would remain in the DDS_DataReader indefinitely.

A DataReader can also reclaim all resources for instances that have an instance state of DDS_NOT_ALIVE_DISPOSED_INSTANCE_STATE and for which all DDS samples have been 'taken'. DataReaders will only reclaim resources in this situation when the autopurge_disposed_instances_delay has been set to zero.

For keyed Topics, the consideration of removing data samples from the receive queue is done on a per instance (key) basis. Thus when RTI Connext detects that there are no longer DataWriters alive for a certain key value of a Topic (an instance of the Topic), it can be configured to remove all data samples for that instance (key).

Entity:

DDS_DataReader

Properties:

RxO = N/A
Changeable = YES

Field Documentation

struct DDS_Duration_t DDS_ReaderDataLifecycleQosPolicy::autopurge_nowriter_samples_delay

Minimum duration for which the DDS_DataReader will maintain information regarding an instance once its instance_state becomes DDS_NOT_ALIVE_NO_WRITERS_INSTANCE_STATE.

At some point after this time elapses, the DDS_DataReader will purge all internal information regarding the instance, any "untaken" samples will also be lost.

[default] DDS_DURATION_INFINITE

[range] [1 nanosec, 1 year] or DDS_DURATION_INFINITE

struct DDS_Duration_t DDS_ReaderDataLifecycleQosPolicy::autopurge_disposed_samples_delay

Minimum duration for which the DDS_DataReader will maintain samples for an instance once its instance_state becomes DDS_NOT_ALIVE_DISPOSED_INSTANCE_STATE.

After this time elapses, the DDS_DataReader will purge all samples for the instance even if they have not been read by the application. This purge is done lazily when space is needed for other samples or instances.

[default] DDS_DURATION_INFINITE

[range] [1 nanosec, 1 year] or DDS_DURATION_INFINITE

struct DDS_Duration_t DDS_ReaderDataLifecycleQosPolicy::autopurge_disposed_instances_delay

<<extension>> Minimum duration for which the DDS_DataReader will maintain information about a received instance once its instance_state becomes DDS_NOT_ALIVE_DISPOSED_INSTANCE_STATE.

After this time elapses, when the last sample for the disposed instance is taken, the DDS_DataReader will keep only the minimum state about the instance.

If you do not want to keep this minimum state after the delay period, also set keep_minimum_state_for_instances to FALSE in DDS_DataReaderResourceLimitsQosPolicy.

The only currently supported values are 0 and DDS_DURATION_INFINITE. A value of 0 will purge an instance's state immediately after the instance state transitions to DDS_NOT_ALIVE_DISPOSED_INSTANCE_STATE, as long as all samples, including the dispose sample, associated with that instance have been 'taken'.

[default] DDS_DURATION_INFINITE