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

An abridged version of this paper appeared in the Proceedings

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...

This paper makes two contributions to the development and evaluation of object-oriented communication software. First, it reports performance results from benchmarking several network programming mechanisms (such as sockets and CORBA) on Ethernet and ATM networks. These results illustrate that developers of high-bandwidth, low-delay applications (such as interactive medical imaging or teleconferencing) must evaluate their performance requirements and the efficiency of their communication infrastructure carefully before adopting a distributed object solution. Second, the paper describes the software architecture and design principles of the ACE object-oriented network programming components. These components encapsulate UNIX and Windows NT network programming interfaces (such as sockets, TLI, and named pipes) with C++ wrappers. Developers of object-oriented communication software have traditionally had to choose between high-performance, lower-level interfaces provided by sockets or TLI...

Efficient and predictable demultiplexing is necessary to provide real-time support for distributed object computing applications developed with CORBA. This paper presents two contributions to the study of demultiplexing for real-time CORBA endsystems. First, we present an empirical study of four CORBA request demultiplexing strategies (linear search, perfect hashing, dynamic hashing, and active demultiplexing) for a range of target objects and operations. Second, we describe how we are using the perfect hashing and active demultiplexing strategies to develop a highperformance, real-time ORB called TAO. Keywords: Communication software, Real-time CORBA, Demultiplexing. 1 Introduction CORBA is a distributed object computing middleware standard defined by the Object Management Group (OMG)[14]. CORBA is designed to allow clients to invoke operations on remote objects without concern for where the object resides or what language the object is written in. In addition, CORBA shields applica...

High-performance Web servers are essential to meet the growing demands of the Internet and large-scale intranets. Satisfying these demands requires a thorough understanding of key factors affecting Web server performance. This paper presents empirical analysis illustrating how dynamic and static adaptivity can enhance Web server performance. Two research contributions support this conclusion. First, the paper presents results from a comprehensive empirical study of Web servers (such as Apache, Netscape Enterprise, PHTTPD, Zeus, and JAWS) over high-speed ATM networks. This study illustrates their relative performance and precisely pinpoints the server design choices that cause performance bottlenecks. We found that once network and disk I/O overheads are reduced to negligible constant factors, the main determinants of Web server performance are its protocol processing path and concurrency strategy. Moreover, no single strategy performs optimally for all load conditions and traffic type...

The realisation of domain-specific languages (DSL DSLs) differs in fundamental ways from that of traditional programming languages. We describe eight recurring patterns that we have identified as being used for DSL design and implementation. Existing languages can be extended, restricted, partially used, or become hosts for DSLs. DSL Simple DSLs DSL can be implemented by lexical processing. In addition, DSLs DSL can be used to create front-ends to existing systems or to express complicated data structures. Finally, DSLs DSL can be combined using process pipelines. The patterns described form a pattern language that can be used as a building block for a systematic

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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...