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

We introduce River, a data-flow programming environment and I/O substrate for clusters of computers. River is designed to provide maximum performance in the common case --- even in the face of nonuniformities in hardware, software, and workload. River is based on two simple design features: a high-performance distributed queue, and a storage redundancy mechanism called graduated declustering. We have implemented a number of data-intensive applications on River, which validate our design with near-ideal performance in a variety of non-uniform performance scenarios.

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...

The Horus system supports a communication architecture that treats protocols as instances of an abstract data type. This approach encourages developers to partition complex protocols into simple microprotocols, each of which is implemented by a protocol layer. Protocol layers can be stacked on top of each other in a variety of ways, at run-time. First, we describe the classes of protocols that can be supported this way. Next, we present the Horus object model that we designed for this technology, and the interface between the layers that makes it all work. We then present an example layer that implements a group membership protocol. Next, we show how, given a set of required properties, an appropriate stack can be constructed. We look at an example stack of protocols, which provides fault-tolerant, totally ordered communication between a group of processes. The work contributes a standard framework for protocol development and experimentation, provides a high performance implementation...

To be an effective platform for performance-sensitive real-time and embedded applications, off-the-shelf CORBA middleware must preserve the communication-layer quality of service (QoS) properties of applications end-to-end. However, the standard CORBA GIOP/IIOP interoperability protocols are not well suited for applications that cannot tolerate the message footprint size, latency, and jitter associated with general-purpose messaging and transport protocols. It is essential, therefore, to develop standard pluggable protocols frameworks that allow custom messaging and transport protocols to be configured flexibly and used transparently by applications. This paper provides three contributions to research on pluggable protocols frameworks for performance-sensitive distributed object computing (DOC) middleware. First, we outline the key design challenges faced by pluggable protocols developers. Second, we describe how we resolved these challenges by developing a pluggable protocols framewo...

Communication-oriented abstractions such as atomic multicast, group RPC, and protocols for location-independent mobile computing can simplify the development of complex applications built on distributed systems. This paper describes Coyote, a system that supports the construction of highly modular and configurable versions of such abstractions. Coyote extends the notion of protocol objects and hierarchical composition found in existing systems with support for finer-grain objects called micro-protocols that implement individual semantic properties of the target service. A customized service is constructed by selecting micro-protocols based on their semantic guarantees and configuring them together with a standard runtime system to form a composite protocol implementing the service. Micro-protocols within a composite protocol can share data and are executed using an event-driven paradigm that enhances configurability. The overall approach is described and illustrated with exampl...

This dissertation shows that operating systems can provide fundamental services an order of magnitude more efficiently than traditional implementations. It describes the implementation of a new operating system kernel, Synthesis, that achieves this level of performance. The Synthesis kernel combines several new techniques to provide high performance without sacrificing the expressive power or security of the system. The new ideas include: ffl Run-time code synthesis --- a systematic way of creating executable machine code at runtime to optimize frequently-used kernel routines --- queues, buffers, context switchers, interrupt handlers, and system call dispatchers --- for specific situations, greatly reducing their execution time. ffl Fine-grain scheduling --- a new process-scheduling technique based on the idea of feedback that performs frequent scheduling actions and policy adjustments (at submillisecond intervals) resulting in an adaptive, self-tuning system that can support real-ti...

The vnode interface has succeeded in supporting a wide range of file system implementations over its 6-year history. During that time it has also had to accommodate evolution in file system semantics, and in the relationship between the file system and the virtual memory system. The effects of this evolution have been less than elegant, and pressures for further evolution are mounting. The evolution of the interface is reviewed in order to identify the problems it has caused, and a more robust revision of the interface design proposed. This design also permits new file systems to be implemented in terms of pre-existing file system implementations; it is more like the Streams interface in this respect. The current state of a prototype implementation is described and its performance characterized. MELENE (lazily). We are very well as we are. Life without a care − every want supplied by a kind and fatherly monarch, who, despot though he be, has no other thought than to make his people happy − what have we to gain by the great change that is in store for us? Gilbert & Sullivan, Utopia, Ltd. 1.

Queueing is an essential element of traffic management, but the only queueing discipline used in traditional UNIX systems is simple FIFO queueing. This paper describes ALTQ, a queueing framework that allows the use of a set of queueing disciplines. We investigate the issues involved in designing a generic queueing framework as well as the issues involved in implementing various queueing disciplines. ALTQ is implemented as simple extension to the FreeBSD kernel including minor fixes to the device drivers. Several queueing disciplines including CBQ, RED, and WFQ are implemented onto the framework to demonstrate the design of ALTQ. The traffic management performance of a PC is presented to show the feasibility of traffic management by PC-UNIX based routers. 1

Developing extensible, robust, and efficient distributed systems is a complex task. To help alleviate this complexity, we have developed the ADAPTIVE Service eXecutive (ASX) framework. ASX is an object-oriented framework composed of automated tools and reusable components. These tools and components help to simplify the development, configuration, and reconfiguration of applications in a distributed environment. Using the ASX framework, the services in the applications may be updated and extended without modifying, recompiling, relinking, or restarting the applications at run-time. This paper describes the features and objectoriented architecture of the ASX framework. It also describes how the ASX framework has been used to develop a highly modular, reusable, and dynamically reconfigurable family of distributed system management applications. 1 Introduction Mapping distributed application services flexibly and efficiently onto host processes and threads is a challenging task. Selectin...