Modern networked computing environments and applications often require---or can benefit from---the use of multiple communication substrates, transport mechanisms, and protocols, chosen according to where communication is directed, what is communicated, or when communication is performed. We propose techniques that allow multiple communication methods to be supported transparently in a single application, with either automatic or user-specified selection criteria guiding the methods used for each communication. We explain how communication link and remote service request mechanisms facilitate the specification and implementation of multimethod communication. These mechanisms have been implemented in the Nexus multithreaded runtime system, and we use this system to illustrate solutions to various problems that arise when implementing multimethod communication. We also illustrate the application of our techniques by describing a multimethod, multithreaded implementation of the Message Pas...

This paper describes PARDIS, a system carrying explicit support for interoperability of PARallel DIStributed applications. PARDIS is closely based on the Common Object Request Broker Architecture (CORBA) [OMG95]. Like CORBA, it provides interoperability between heterogeneous components by specifying their interfaces in a meta-language, the CORBA IDL, which can be translated into the language of interacting components, also providing interaction in a distributed domain. In order to provide support for interacting parallel applications, PARDIS extends the CORBA object model by a notion of an SPMD object. SPMD objects allow the request broker to interact directly with the distributed resources of a parallel application. To support distributed argument transfer, PARDIS introduces the notion of a distributed sequence --- a generalization of a CORBA sequence representing distributed data structures of parallel applications. In this report we will give a brief description of basic component i...

The coordinated use of geographically distributed computers, or metacomputing, can in principle provide more accessible and cost-effective supercomputing than do conventional highperformance systems. However, we lack evidence that metacomputing systems can be made easily usable or that large numbers of applications are able to exploit metacomputing resources. In this article, we present work that addresses both these concerns. The basis for this work is a system called Nimrod that provides a desktop problemsolving environment for parametric experiments. We describe how Nimrod has been extended to support the scheduling of computational resources located in a wide-area environment and report Proceedings of the 20th Australasian Computer Science Conference, Sydney, Australia, February 5--7 1997. on an experiment in which Nimrod was used to schedule a large parametric study across the Australian Internet. The experiment provided both new scientific results and insights into Nimrod capabi...

We describe a software infrastructure designed to support the development of applications that use high-speed networks to connect geographically distributed supercomputers, databases, and scientific instruments. Such applications may need to operate over open networks and access valuable resources, and hence can require mechanisms for ensuring integrity and confidentiality of communications and for authenticating both users and resources. Yet security solutions developed for traditional client-server applications do not provide direct support for the distinctive program structures, programming tools, and performance requirements encountered in these applications. To address these requirements, we are developing a security-enhanced version of a communication library called Nexus, which is then used to provide secure versions of various parallel libraries and languages, including the popular Message Passing Interface. These tools support the wide range of process creation mechan...

High-speed wide-area networks enable innovative ap-plications that integrate geographically distributed com-puting, database, graphics, and networking resources. The Message Passing Interface (MPI) can be used as a portable, high-performance programming model for such systems. However, the wide-area environment in-troduces challenging problems for the MPI implementor, because of the heterogeneity of both the underlying physical infrastructure and the authentication and software environment at different sites. In this article, we describe an MPI implementation that incorporates so-lutions to these problems. This implementation, which was developed for the I-WAY distributed-computing ex-periment, was constructed by layering MPICH on the Nexus multithreaded runtime system. Nexus provides automatic configuration mechanisms that can be used to select and configure authentication, process creation, and communication mechanisms in heterogeneous systems.

: Modern technology provides the infrastructure necessary to develop distributed applications capable of using the power of multiple supercomputing resources and exploiting their diversity. The performance potential offered by distributed supercomputing is enormous, but it is hard to realize due to the complexity of programming in such environments. In this paper we introduce PARDIS, a system designed to overcome this challenge, based on ideas underlying the Common Object Request Broker Architecture (CORBA), a successful industry standard. PARDIS is a distributed environment in which objects representing data-parallel computations, called SPMD objects, as well as non-parallel objects present in parallel programs, can interact with each other across platforms and software systems. Each of these objects represents a small encapsulated application and can be used as a building block in the construction of powerful distributed metaapplications. The objects interact through interfaces spec...

We consider networks of workstations which are not only timesharing, but also heterogeneous with a large variation in the computing power and memory capacities of different workstations. Many load sharing schemes mainly target sharing CPU resources, and have been intensively evaluated in homogeneous distributed environments. However, the penalties of data accesses and movement in modern computer systems, such as page faults, have grown to the point where the overall performance of distributed systems cannot be further improved without serious considerations concerning memory resources in the design of load sharing policies. Considering both system heterogeneity and effective usage of memory resources, we design and evaluate load sharing policies in order to minimize both CPU idle times and the number of page faults in heterogeneous distributed systems. Conducting trace-driven simulations, we show that load sharing policies considering both CPU and memory resources are robust and effect...

In this article, we present the Mocha wide area computing infrastructure we are currently developing. Mocha provides support for robust shared objects on heterogeneous platforms, and utilizes advanced distributed shared memory techniques for maintaining consistency of shared objects that are replicated at multiple nodes to improve performance. In addition, our system handles failures that we feel will be common in wide area environments. For example, to ensure that the state of an object is not lost due to a node failure, updated state of the object can be disseminated to several other nodes. The overhead of such state dissemination can be controlled based on the level of availability needed for shared objects. We have used an approach that makes use of multiple communication protocols to improve the efficiency of shared object state transfers in Mocha. We also provide an empirical evaluation of our prototype implementation for local area, wide area, and home service networks and show ...

We use the term ubiquitous supercomputing to refer to systems that integrate low- and mid-range computing systems, advanced networks, and remote highend computers with the goal of enhancing the computational power accessible from local environments. Such systems promise to enable new applications in areas as diverse as smart instruments and collaborative environments. However, they also demand tools for transporting code between computers and for establishing flexible, dynamic communication structures. In this article, we propose that these requirements be satisfied by introducing Java classes that implement the global pointer and remote service request mechanisms defined by a communication library called Nexus. Java supports transportable code; Nexus provides communication support and represents the core communication framework for Globus, a project building infrastructure for ubiquitous supercomputing. We explain how this NexusJava library is implemented and illustrate its use with e...

ions for Distributed Supercomputing Katarzyna Keahey Dennis Gannon Department of Computer Science Indiana University 215 Lindley Hall Bloomington, IN 47405 E-mail: keahey@cs.indiana.edu To fully realize its potential, distributed supercomputing requires abstractions and environments facilitating development of efficient applications. In this paper we present PARDIS, a system which addresses this demand by providing support for interoperability of PARallel DIStributed applications. The design of PARDIS is based on the Common Object Request Broker Architecture (CORBA). Like CORBA, it provides interoperability between heterogeneous components by specifying their interfaces in a meta-language, the CORBA IDL, which can be translated into the language of interacting components. However, PARDIS extends the CORBA object model by introducing SPMD objects representing data-parallel computations. This extension allows us to build interactions involving data-parallel components, which exchange ...