Advances in networking technologies will soon make it possible to use the global information infrastructure in a qualitatively different way—as a computational resource as well as an information resource. This idea for an integrated computation and information resource called the Computational Power Grid has been described by the recent book entitled The Grid: Blueprint for a New Computing Infrastructure [18]. The Grid will connect the nation’s computers, databases, instruments, and people in a seamless web, supporting emerging computation-rich application concepts such as remote computing, distributed supercomputing, tele-immersion, smart instruments, and data mining. To realize this vision, significant scientific and technical obstacles must be overcome. Principal among these is usability. Because the Grid will be inherently more complex than existing computer systems, programs that execute on the Grid will reflect some of this complexity. Hence, making Grid resources useful and accessible to scientists and engineers will require new software tools that embody major advances in both the theory and practice of building Grid applications. The goal of the Grid Application Development Software (GrADS) Project is to simplify distributed heterogeneous computing in the same way that the World Wide Web simplified information sharing

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

Distributed object computing forms the basis for nextgeneration application middleware. At the heart of distributed object computing are Object Request Brokers (ORBs), which automate many tedious and error-prone distributed programming tasks. This article presents a case study of key design patterns needed to develop ORBs that can be dynamically configured and evolved for specific application requirements and system characteristics.

There is increasing demand to extend object-oriented middleware, such as OMG CORBA, to support applications with stringent quality of service (QoS) requirements. However, conventional CORBA Object Request Broker (ORB) implementations incur high latency and low scalability when used for performance-sensitive applications. These inefficiencies discourage developers from using CORBA for mission/lifecritical applications such as real-time avionics, telecom call processing, and medical imaging. This paper provides two contributions to the research on CORBA performance. First, we systematically analyze the latency and scalability of two widely used CORBA ORBs, VisiBroker and Orbix. These results reveal key sources of overhead in conventional ORBs. Second, we describe techniques used to improve latency and scalability in TAO, which is a high-performance, real-time implementation of CORBA. Although conventional ORBs do not yet provide adequate QoS guarantees to applications, our research resu...

Abstract not found

This paper will appear in the Communications of the ACM Special Issue on CORBA edited by Krishnan Seetharaman, October 1998, Vol. 41, No. 10. Introduction

This paper presents two contributions to the study of CORBA performance over high-speed networks. First, we measure the latency of various types and sizes of twoway client requests using a pair of widely used implementations of CORBA -- Orbix 2.1 and VisiBroker for C++ 2.0. Second, we use Orbix and VisiBroker to measure the scalability of CORBA servers in terms of the number of objects they can support efficiently. These experiments extend our previous work on CORBA performance for bandwidth-sensitive applications (such as satellite surveillance, medical imaging, and teleconferencing). Our results show that the latency for CORBA implementations is relatively high and server scalability is relatively low. Our latency experiments show that non-optimized internal buffering in CORBA implementations can cause substantial delay variance, which is unacceptable in many real-time or constrained-latency applications. Likewise, our scalability experiments reveal that neither Orbix nor VisiBroker...

Historically, method-oriented middleware, such as Sun RPC, DCE, Java RMI, COM, and CORBA, has provided synchronous method invocation (SMI) models to applications. Although SMI works well for conventional client/server applications, it is not well-suited for high-performance or real-time applications due to its lack of scalability. To address this problem, the OMG has recently standardized an asynchronous method invocation (AMI) model for CORBA. AMI provides CORBA with many of the capabilities associated traditionally with message-oriented middleware, without incurring the key drawbacks of message-oriented middleware. This paper provides two contributions to research on asynchronous invocation models for method-oriented middleware. First, we outline the key design challenges faced when developing the CORBA AMI model and describe how we resolved these challenges in TAO, which is our high-performance, real-time CORBA-compliant ORB. Second, we present the results of empirical benchmarks t...

Distributed object computing (DOC) middleware shields developers from many tedious and error-prone aspects of programming distributed applications. Without proper support from the middleware, however, it can be hard to evolve distributed applications after they are deployed. Therefore, DOC middleware should support meta-programming mechanisms, such as smart proxies and interceptors, that improve the adaptability of distributed applications by allowing their behavior to be modified without changing existing software drastically.

In this paper we describe our experience with Teapot [7], a domain-specific language for addressing the cache coherence problem. The cache coherence problem arises when parallel and distributed computing systems make local replicas of shared data for reasons of scalability and performance.