Public Attributes | |
DestinationOrderQosPolicyKind | kind |
Specifies the desired kind of destination order. | |
final Duration_t | source_timestamp_tolerance |
<<eXtension>> Allowed tolerance between source timestamps of consecutive samples. |
This QoS policy controls how each subscriber resolves the final value of a data instance that is written by multiple com.rti.dds.publication.DataWriter entities (which may be associated with different com.rti.dds.publication.Publisher entities) running on different nodes.
The default setting, DestinationOrderQosPolicyKind.BY_RECEPTION_TIMESTAMP_DESTINATIONORDER_QOS, indicates that (assuming the OWNERSHIP_STRENGTH policy allows it) the latest received value for the instance should be the one whose value is kept. That is, data will be delivered by a com.rti.dds.subscription.DataReader in the order in which it was received (which may lead to inconsistent final values).
The setting DestinationOrderQosPolicyKind.BY_SOURCE_TIMESTAMP_DESTINATIONORDER_QOS indicates that (assuming the OWNERSHIP_STRENGTH allows it, within each instance) the source_timestamp
of the change shall be used to determine the most recent information. That is, data will be delivered by a com.rti.dds.subscription.DataReader in the order in which it was sent. If data arrives on the network with a source timestamp that is later than the source timestamp of the last data delivered, the new data will be dropped. This 'by source timestamp' ordering therefore works best when system clocks are relatively synchronized among writing machines.
When using DestinationOrderQosPolicyKind.BY_SOURCE_TIMESTAMP_DESTINATIONORDER_QOS, not all data sent by multiple com.rti.dds.publication.DataWriter entities may be delivered to a com.rti.dds.subscription.DataReader and not all DataReaders will see the same data sent by DataWriters. However, all DataReaders will see the same "final" data when DataWriters "stop" sending data. This is the only setting that, in the case of concurrently publishing com.rti.dds.publication.DataWriter entities updating the same instance of a shared-ownership topic, ensures all subscribers will end up with the same final value for the instance.
This QoS can be used to create systems that have the property of "eventual consistency." Thus intermediate states across multiple applications may be inconsistent, but when DataWriters stop sending changes to the same topic, all applications will end up having the same state.
Specifies the desired kind of destination order.
[default] DestinationOrderQosPolicyKind.BY_RECEPTION_TIMESTAMP_DESTINATIONORDER_QOS,
<<eXtension>> Allowed tolerance between source timestamps of consecutive samples.
When a com.rti.dds.publication.DataWriter sets com.rti.dds.infrastructure.DestinationOrderQosPolicyKind to DestinationOrderQosPolicyKind.BY_SOURCE_TIMESTAMP_DESTINATIONORDER_QOS, when when writing a sample, its timestamp must not be less than the timestamp of the previously written sample. However, if it is less than the timestamp of the previously written sample but the difference is less than this tolerance, the sample will use the previously written sample's timestamp as its timestamp. Otherwise, if the difference is greater than this tolerance, the write will fail.
When a com.rti.dds.subscription.DataReader sets com.rti.dds.infrastructure.DestinationOrderQosPolicyKind to DestinationOrderQosPolicyKind.BY_SOURCE_TIMESTAMP_DESTINATIONORDER_QOS, the com.rti.dds.subscription.DataReader will accept a sample only if the difference between its source timestamp and the reception timestamp is no greater than this tolerance. Otherwise, the sample is rejected.
[default] 100 milliseconds for com.rti.dds.publication.DataWriter, 30 seconds for com.rti.dds.subscription.DataReader