The design and performance of a real-time notification service

Many distributed real-time and embedded (DRE) applications require a scalable event-driven communication model that decouples suppliers from consumers and simultaneously supports advanced quality of service (QoS) properties and event filtering mechanisms. The CORBA notification service provides publisher/subscriber capabilities designed to support scalable event-driven communication by routing events efficiently between suppliers and consumers, enforcing QoS properties (such as reliability, priority, ordering, and timeliness), and filtering events at multiple points in a distributed system. The standard CORBA notification service is insufficient, however, to enforce predictable communication needed by DRE applications and does not leverage real-time CORBA capabilities, such as end-to-end priority assignment or scheduling services. We make three contributions to the study of scalable real-time notification services for DRE applications. First, we describe the requirements of the OMG request for proposals (RFP) on real-time notification, which seeks solutions to the problem of enforcing real-time properties by enhancing the standard CORBA notification service. Second, we explain how we have addressed key design challenges faced when implementing a real-time notification service for TAO, which is our CORBA-compliant real-time object request broker (ORB). We discuss how we integrate real-time CORBA features (such as thread pools, thread lanes, and priority models) to provide real-time event communication. Finally, we analyze the results of empirical benchmarks of the performance and predictability of TAO's real-time notification service. These results show that the static real-time assurances provided by real-time CORBA are maintained within the more flexible context of TAO's real-time notification service.