You are here: Part 2: Core Concepts > Sending Data > DataWriter QosPolicies > WRITER_DATA_LIFECYCLE QoS Policy


This QoS policy controls how a DataWriter handles the lifecycle of the instances (keys) that the DataWriter is registered to manage. This QoS policy includes the members in .



Field Name




RTI_TRUE (default): Instance is disposed when unregistered.

RTI_FALSE: Instance is not disposed when unregistered.

struct DDS_Duration_t


Determines how long the DataWriter will maintain information regarding an instance that has been unregistered.

By default, the DataWriter resources associated with an instance (e.g., the space needed to remember the Instance Key or KeyHash) are released lazily. This means the resources are only reclaimed when the space is needed for another instance because max_instances (see RESOURCE_LIMITS QosPolicy) is exceeded. This behavior can be changed by setting autopurge_unregistered_instance_delay to a value other than INFINITE.

After this time elapses, the DataWriter will purge all internal information regarding the instance, including historical DDS samples even if max_instances has not been reached.

You may use the DataWriter’s unregister() operation (Registering and Unregistering Instances) to indicate that the DataWriter no longer wants to send data for a Topic. This QoS controls whether or not Connext DDS automatically also calls dispose() (Disposing of Data) on the behalf of the DataWriter for the data.

Unregistering vs. Disposing:

The behavior controlled by this QoS applies on a per instance (key) basis for keyed Topics, so when a DataWriter unregisters an instance, Connext DDS also automatically disposes that instance. This is the default behavior since autodispose_unregistered_instances defaults to TRUE.

Use Cases for Unregistering without Disposing:

There are situations in which you may want to set autodispose_unregistered_instances to FALSE, so that unregistering will not automatically dispose the instance. For example:

When you delete a DataWriter (Creating DataWriters), all of the instances managed by the DataWriter are automatically unregistered. Therefore, this QoS policy determines whether or not all of the instances are disposed when the DataWriter is deleted when you call one of these operations:

When autodispose_unregistered_instances is TRUE, the middleware will clean up all the resources associated with an unregistered instance (most notably, the DDS sample history of non-volatile DataWriters) when all the instance’s DDS samples have been acknowledged by all its live DataReaders, including the DDS sample that indicates the unregistration. By default, autopurge_unregistered_instances_delay is disabled (the delay is INFINITE). If the delay is set to zero, the DataWriter will clean up as soon as all the DDS samples are acknowledged after the call to unregister(). A non-zero value for the delay can be useful in two ways:

This delay can also be set for discovery data through these fields in the DISCOVERY_CONFIG QosPolicy (DDS Extension):


It does not apply to DataReaders, so there is no requirement that the publishing and subscribing sides use compatible values.

This QoS policy may be modified after the DataWriter is enabled.

Related QoS Policies

Applicable Entities

System Resource Considerations


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