Deadlines and Content Filtering

Concept

In RTI Connext DDS, you can use the DEADLINE QoS to specify that you expect updates about a particular instance within a given period of time.

This QoS is request-offered, meaning that the DataWriter offers a level of service, and the DataReader requests a level of service. Request-offered QoS are like a contract between the DataWriter and the DataReader: the DataWriter is saying that it will provide a level of service, and the DataReader is saying it requires a level of service. The offered level must be greater than or equal to the requested level, or there will be no communication between the DataWriter and the DataReader.

However, the middleware cannot enforce the DEADLINE contract, because that is subject to:

1. how often the application calls write()
2. whether the network loses packets
3. whether the reader application is filtering some of the data

So, the middleware is responsible for:

1. Notifying the DataWriter application if the DataWriter is not writing as often as it specified in its DEADLINE period
2. Notifying the DataReader application if data did not arrive within its DEADLINE period

Example Description

This example shows:

1. The DataWriter writing two instances, both of them fast enough to satisfy the DEADLINE period
2. After 10 seconds, the DataReader uses a Content-Filtered Topic to filter out one of those instances. The DataReader now gets notifications that it is not receiving that instance within the DEADLINE period, and prints out which instance is not being received on time.
3. After 15 seconds, the DataWriter no longer writes one of the instances. Now the DataWriter is notified that it is failing to meet its DEADLINE contract for that instance.

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