The ADAPTIVE Communication Environment (ACE) is an object-oriented toolkit that implements strategic and tactical design patterns to simplify the development of concurrent, event-driven communication software. ACE provides a rich set of reusable C++ wrappers, class categories, and frameworks that perform common communication software tasks across a range of operating system platforms. The communication software tasks provided by ACE include event demultiplexing, event handler dispatching, connection establishment, interprocess communication, shared memory management, message routing, dynamic (re)configuration of network services, multi-threading, and concurrency control. ACE is targeted for developers of high-performance concurrent network applications and services. The primary goal of ACE is to simplify the development of concurrent OO communication software that utilizes interprocess communication, event demultiplexing, explicit dynamic linking, and concurrency. In addition, ACE auto...

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

Conventional implementations of communication middleware (such as CORBA and traditional RPC toolkits) incur considerable overhead when used for performance-sensitive applications over high-speed networks. As gigabit networks become pervasive, inefficient middleware will force programmers to use lower-level mechanisms to achieve the necessary transfer rates. This is a serious problem for mission/lifecritical applications (such as satellite surveillance and medical imaging). This paper compares the performance of several widely used communication middleware mechanisms on a highspeed ATM network. The middleware ranged from lowerlevel mechanisms (such as socket-based C interfaces and C++ wrappers for sockets) to higher-level mechanisms (such as RPC, hand-optimized RPC and two implementations of CORBA -- Orbix 2.0.1 and ORBeline 2.0). These measurements reveal that the lower-level C and C++ implementations outperform the CORBA implementations significantly (the best CORBA throughput for rem...

Many application domains (such as avionics, telecommunications, and multimedia) require real-time guarantees from the underlying networks, operating systems, and middleware components to achieve their quality of service (QoS) requirements. In addition to providing end-to-end QoS guarantees, applications in these domains must be flexible and reusable. Requirements for flexibility and reusability motivate the use of object-oriented middleware like the Common Object Request Broker Architecture (CORBA). However, the performance of current CORBA implementations is not yet suited for hard real-time systems (e.g., avionics) and constrained latency systems (e.g., teleconferencing). This paper describes the architectural features and optimizations required to develop real-time ORB endsystems that can deliver end-to-end QoS guarantees to applications. While some operating systems, networks, and protocols now support real-time scheduling, they do not provide integrated solutions. The main thrust ...

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...

The Common Object Request Broker Architecture (CORBA) is intended to simplify the task of developing distributed applications. Although it is well-suited for conventional RPCstyle applications, several limitations become evident when CORBA is used for a broader range of performance-sensitive applications running in heterogeneous environments over high-speed networks. This paper illustrates the performance limitations of existing CORBA implementations in terms of their support for the dynamic invocation interface and the dynamic skeleton interface. The results described below indicate that ORB implementors must optimize both the DII and DSI significantly before CORBA will be suitable for performance-sensitive applications on high-speed networks. In addition, the CORBA 2.0 DII specification must be clarified in order to ensure application portability and optimal performance. 1 Introduction The Common Object Request Broker Architecture (CORBA) [9]) is a promising approach for improving t...

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...

This paper describes the Service Configurator pattern, which decouples the implementation of services from the time when they are configured. This pattern increases the flexibility and extensibilityof applicationsby enabling their constituent services to be configured at any point in time. The Service Configurator pattern is widely used in application environments (e.g., to configure Java applets into WWW browsers), operating systems (e.g., to configure device drivers), and distributed systems (e.g., to configure standard Internet communication services).

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...