Real-time Object Request Broker Research Articles

FCS/nORB: A feedback control real-time scheduling service for embedded ORB middleware

Object Request Broker (ORB) middleware has shown promise in meeting the functional and real-time performance requirements of distributed real-time and embedded (DRE) systems. However, existing real-time ORB middleware standards such as RT-CORBA do not adequately address the challenges of (1) managing unpredictable workload, and (2) providing robust performance guarantees portably across different platforms. To overcome this limitation, we have developed software called FCS/nORB that integrates a Feedback Control real-time Scheduling (FCS) service with the nORB small-footprint real-time ORB designed for networked embedded systems. FCS/nORB features feedback control loops that provide real-time performance guarantees by automatically adjusting the rate of remote method invocations transparently to an application. FCS/nORB thus enables real-time applications to be truly portable in terms of real-time performance as well as functionality, without the need for hand tuning. This paper presents the design, implementation, and empirical evaluation of FCS/nORB. Our extensive experiments on a Linux testbed demonstrate that FCS/nORB can provide deadline miss ratio and utilization guarantees in the face of changes in platform and task execution times, while introducing only a small amount of overhead.

FC-ORB: A robust distributed real-time embedded middleware with end-to-end utilization control

A key challenge for distributed real-time and embedded (DRE) middleware is maintaining both system reliability and desired real-time performance in unpredictable environments where system workload and resources may fluctuate significantly. This paper presents FC-ORB, a real-time Object Request Broker (ORB) middleware that employs end-to-end utilization control to handle fluctuations in application workload and system resources. The contributions of this paper are three-fold. First, we present a novel utilization control service that enforces desired CPU utilization bounds on multiple processors by adapting the rates of end-to-end tasks within user-specified ranges. Second, we describe a set of middleware-level mechanisms designed to support end-to-end tasks and distributed multi-processor utilization control in a real-time ORB. Finally, we present extensive experimental results on a Linux testbed. Our results demonstrate that our middleware can maintain desired utilizations in face of uncertainties and variations in task execution times, resource contentions from external workloads, and permanent processor failure. FC-ORB demonstrates that the integration of utilization control, end-to-end scheduling, and fault-tolerance mechanisms in DRE middleware is a promising approach for enhancing the robustness of DRE applications in unpredictable environments.

Software architectures for reducing priority inversion and non-determinism in real-time object request brokers

There is increasing demand to extend Object Request Broker (ORB) middleware to support distributed applications with stringent real-time requirements. However, conventional ORB implementations, such as CORBA ORBs, exhibit substantial priority inversion and non-determinism, which makes them unsuitable for applications with deterministic real-time requirements. This paper provides two contributions to the study and design of real-time ORB middleware. First, it illustrates empirically why conventional ORBs do not yet support real-time quality of service. Second, it evaluates connection and concurrency software architectures to identify strategies that reduce priority inversion and non-determinism in real-time CORBA ORBs. The results presented in this paper demonstrate the feasibility of using standard OO middleware like CORBA to support certain types of real-time applications over the Internet.

The design of the TAO real-time object request broker

Many real-time application domains can benefit from flexible and open distributed architectures, such as those defined by the CORBA specification. CORBA is an architecture for distributed object computing being standardized by the OMG. Although CORBA is well-suited for conventional request/response applications, CORBA implementations are not yet suited for real-time applications due to the lack of key quality of service (QoS) features and performance optimizations. This paper makes three contributions to the design of real-time CORBA systems. First, the paper describes the design of TAO, which is our high-performance, real-time CORBA 2.0-compliant implementation that runs on a range of OS platforms with real-time features including VxWorks, Chorus, Solaris 2.x, and Windows NT. Second, it presents TAO's real-time scheduling service that can provide QoS guarantees for deterministic real-time CORBA applications. Finally, the paper presents performance measurements that demonstrate the effects of priority inversion and non-determinism in conventional CORBA implementations and how these hazards are avoided in TAO.

An overview of the CORBA portable object adapter

An Object Adapter is an integral part of the Common Object Request Broker Architecture (CORBA). An Object Adapter assists an Object Request Broker (ORB) in delivering client requests to server object implementations (servants). Services provided by an Object Adapter include: (1) generating and interpreting object references, (2) activating and deactivating servants, (3) demultiplexing requests to map object references onto their corresponding servants, and (4) collaborating with automatically-generated IDL skeletons to invoke operations on servants. This paper provides two contributions to the study of Object Adapters. First, it outlines the CORBA Portable Object Adapter (POA) specification, which is a recent addition to the CORBA standard that greatly simplifies the development of portable and extensible servants and server applications. The design goals, architectural components, and semantics of the POA are explained. Second, the paper describes the design choices made to adapt the POA for the TAO Real-time ORB. Key design issues regarding efficient demultiplexing, upcall and collocation optimizations, ORB and POA concurrency configurations, POA synchronization, and predictability are covered.