Towards predictable real-time Java object request brokers

Distributed real-time and embedded (DRE) applications often possess stringent quality of service (QoS) requirements. Designing middleware for DRE applications poses several challenges to object request broker (ORB) developers. This paper provides the following contributions to the study of middleware for DRE applications. First, we outline the challenges present in one of the principal ORB components - the portable object adapter (POA) focusing on predictable and scalable demultiplexing. Second, we describe how these challenges are addressed in ZEN, which is an implementation of Real-time CORBA that runs atop jRate, an ahead-of-time compiler that implements most of the Real-Time Specification for Java (RTSJ). Third, we qualitatively and quantitatively compare ZEN's demultiplexing strategies with those of other popular Java ORBs, including JacORB, Sun JDK ORB, and ORBacus. Our results show that ZEN and jRate incorporate the strategies necessary to enable predictability using standards-based middleware and also provide a baseline for what can be achieved by combining Real-time CORBA and RTSJ.