The CORBA Event Service provides a flexible model for asynchronous communication among objects. However, the standard CORBA Event Service specification lacks important features required by real-time applications. For instance, operational flight programs for fighter aircraft have complex realtime processing requirements. This paper describes the design and performance of an object-oriented, real-time implementation of the CORBA Event Service that is designed to meet these requirements. This paper makes three contributions to the design and performance measurement of object-oriented real-time systems. First, it illustrates how to extend the CORBA Event Service so that it is suitable for real-time systems. These extensions support periodic rate-based event processing and efficient event filtering and correlation. Second, it describes how to develop object-oriented event dispatching and scheduling mechanisms that can provide real-time guarantees. Finally, the paper presents benchmarks tha...

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 realtime CORBA systems. First, the paper describes the design of TAO, which is our high-performance, real-time CORBAcompliant 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 realtime 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. 1

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.

There is increasing demand to extend object-oriented middleware to support applications with stringent quality of service (QoS) requirements. However, conventional object-oriented middleware does not define standard features for specifying or enforcing end-to-end QoS for applications with deterministic or statistical real-time requirements. This paper focuses on strategies for integrating I/O subsystems with object-oriented middleware to produce ORB endsystems for statically scheduled real-time applications. Keywords: Real-time CORBA, Object Request Broker, Quality of Service, OO Middleware, I/O Subsystem 1 Introduction Existing Object Request Broker (ORB) middleware like CORBA [1], DCOM [2], and Java RMI [3] is suitable for request /response applications with best-effort quality of service requirements. However, existing ORB middleware is not yet suited for performance-sensitive, distributed real-time applications due to (1) lack of QoS specification interfaces, (2) lack of QoS enfo...

There is increasing demand to extend Object Request Broker (ORB) middleware to support distributed applications with stringent real-time requirements. However, lack of proper OS support can yield substantial inefficiency and unpredictability for ORB middleware. This paper provides two contributions to the study of OS support for real-time ORBs. First, we empirically compare and evaluate the suitability of real-time operating systems, VxWorks and LynxOS, and general-purpose operating systems with real-time extensions, Windows NT, Solaris, and Linux, for real-time ORB middleware. While holding the hardware and ORB constant, we vary the operating system and measure platform-specific variations, such as latency, jitter, operation throughput, and CPU processing overhead. Second, we describe key areas where these operating systems must improve to support predictable, efficient, and scalable ORBs. Our findings illustrate that general-purpose operating systems like Windows NT and Solaris are...

This paper compares and evaluates the suitability of realtime operating systems, VxWorks and LynxOS, and generalpurpose operating systems with real-time extensions, Windows NT, Solaris, and Linux, for real-time ORB middleware. While holding the hardware and ORB constant, we vary these operating systems and measure platform-specific variations in context switching overhead and priority inversions. Our findings illustrate that general-purpose operating systems like Windows NT, Solaris, and Linux are not yet suited to meet the demands of applications with stringent QoS requirements. Although Linux provides good raw performance, its high jitter makes it unsuitable for real-time applications. Both LynxOS and VxWorks do enable predictable and efficient ORB performance, however, thereby making them suitable as OS platforms for real-time CORBA applications. In general, our results underscore the need for a measure-driven methodology to pinpoint sources of overhead and priority inversion in re...

Many types of applications can benefit from flexible and open middleware. CORBA is an emerging middleware standard for Object Request Brokers (ORBs) that simplifies the development of distributed applications and services. Experience with CORBA demonstrates that it is suitable for traditional RPC-style applications. However, the lack of performance optimizations and quality of service (QoS) features in conventional CORBA implementations make them unsuited for highperformance and real-time applications. This paper makes four contributions to the design of CORBA ORBs for applications with high-performance and real-time requirements. First, it describes the design of TAO, which is our high-performance, real-time CORBA-compliant ORB. Second, it presents TAO's Real-time Scheduling Service, which provides QoS guarantees for deterministic realtime CORBA applications. Third, empirically evaluates the effects of priority inversion and non-determinism in conventional ORBs and shows how these ha...

There is increasing demand to extend Object Request Broker (ORB) middleware to support applications with stringent quality of service (QoS) requirements. However, conventional ORBs do not define standard features for specifying or enforcing end-to-end QoS for applications with deterministic realtime requirements. This paper describes the design and performance of a real-time I/O (RIO) subsystem optimized for QoS-enabled ORB endsystems that support high-performance and real-time applications running on off-the-shelf hardware and software. The paper illustrates how integrating a realtime ORB with a real-time I/O subsystem can reduce latency bounds on end-to-end communication between high-priority clients without unduly penalizing low-priority and best-effort clients. Keywords: Real-time CORBA Object Request Broker, Quality of Service for OO Middleware, Real-time I/O Subsystems. 1 Introduction Object Request Broker (ORB) middleware like CORBA [1] and DCOM [2] is well-suited for request/...

There is increasing demand to extend Object Request Broker (ORB) middleware to support applications with stringent quality of service (QoS) requirements. However, conventional ORBs do not define standard features for specifying or enforcing end-to-end QoS for applications with deterministic realtime requirements. This paper provides two contributions to the study of real-time ORB middleware. First, it describes the design of a real-time I/O (RIO) subsystem optimized for ORB endsystems that support statically scheduled real-time applications running on "off-the-shelf " hardware and software. Second, it illustrates how integrating a real-time ORB with a real-time I/O subsystem can reduce latency bounds on end-to-end communication between high-priority clients without penalizing low-priority and best-effort traffic.

There is increasing demand to extend Object Request Broker (ORB) middleware to support applications with stringent quality of service (QoS) requirements. In particular, distributed multimedia applications require efficient and predictable performance from the middleware layer and below to deliver necessary end-to-end QoS. Although ORB middleware, such as CORBA, COM+, and Java RMI, offers transparent distribution, the QoS that it can provide depends largely on the support from the underlying endsystems and networks. This paper provides two contributions to the study of OS endsystem support for real-time ORB middleware. First, we empirically compare and evaluate the suitability of real-time operating systems, VxWorks and LynxOS, and general-purpose operating systems with real-time scheduling classes, Windows NT, Solaris, and Linux, for real-time ORB middleware. While holding the hardware and ORB constant, we systematically vary the OS and measure key platform-specific variations in late...