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.

Factory, Builder, and Service Configurator) the ACE framework components facilitate the development of communication software that may be updated and extended without modifying, recompiling, relinking, or even restarting running systems [6]. 3.1.4 Self-contained Distributed Service Components ACE provides a standard library of distributed services that are packaged as self-contained components. Although these service components are not strictly part of the ACE framework, they play two important roles: Factoring out reusable distributed application building blocks: These service components provide reusable implementations of common distributed application tasks such as naming, event routing, logging, time synchronization, and network locking; Demonstrating common use-cases of ACE: These distributed services also demonstrate how ACE components (such as Reactors, Service Configurators, Acceptors and Connectors, Active Objects, and IPC wrappers) can be used effectively to develop flexi...

Increasingly complex requirements, coupled with with tighter economic and organizational constraints, are making it hard to build complex distributed real-time embedded (DRE) systems entirely from scratch. The proportion of DRE systems made up of commercial-off-the-shelf (COTS) hardware and software is therefore increasing significantly. There are relatively few systematic empirical studies, however, that illustrate how suitable COTS-based hardware and software have become for mission-critical DRE systems. This paper provides the following contributions to the study of real-time quality of service (QoS) assurance and performance in COTS-based DRE systems: (1) it presents evidence that flexible configuration of COTS middleware mechanisms, and the operating system settings they use, allows DRE systems to meet critical QoS requirements over a wider range of load and jitter conditions than statically configured systems, (2) it shows that in addition to making critical QoS assurances, non-critical QoS performance can be improved through flexible support for alternative scheduling strategies, and (3) it presents an empirical study of three canonical scheduling strategies---specifically the conditions that predict success of a strategy for a production-quality DRE avionics mission computing system. Our results show that applying a flexible scheduling framework to COTS hardware, operating systems, and middleware improves real-time QoS assurance and performance for mission-critical DRE systems.

End-to-end predictability of remote operations is essential for many fixed-priority distributed real-time and embedded (DRE) applications, such as command and control systems, manufacturing process control systems, large-scale distributed interactive simulations, and testbeam data acquisition systems. To enhance predictability, the Real-time CORBA specification defines standard middleware features that allow applications to allocate, schedule, and control key CPU, memory, and networking resources necessary to ensure end-to-end quality of service support.

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...

Distributed object computing forms the basis of nextgeneration communication software. At the heart of distributed object computing are Object Request Brokers (ORBs), which automate many tedious and error-prone distributed programming tasks. Like much communication software, conventional ORBs use statically configured designs, which are hard to port, optimize, and evolve. Likewise, conventional ORBs cannot be extended without modifying their source code, which forces recompilation, relinking, and restarting running ORBs and their associated application objects. This paper makes two contributions to the study of extensible ORB middleware. First, it presents a case study illustrating how a pattern language can be used to develop dynamically configurable ORBs that can be customized for specific application requirements and system characteristics. Second, we quantify the impact of applying this pattern language to reduce the complexity and improve the maintainability of common ORB tasks, ...

Distributed computing is one of the major trends in the computer industry. As systems become more distributed, they also become more complex and have to deal with new kinds of problems, such as partial crashes and link failures. While many middleware architectures have emerged to answer the growing demand in distributed technologies, most of them do not provide any kind of fault tolerance mechanisms. In this paper, we discuss the addition of object group support to CORBA. We describe

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 article compares different approaches for developing Java distributed applications which have to communicate