The Mach external pager interface allows applications to supply their own routines for moving pages to and from second-level store. Mach doesn't allow applications to choose their own page replacement policy, however. Some applications have access patterns that may make least recently used page replacement inappropriate. In this paper, we describe an extension to the external pager interface that allows the programmer to specify the page replacement policy as well as the backing storage for a region of virtual memory. 1 Introduction An operating system attempts to be all things to all users. Because of this, sometimes compromises have to be made; performance may be sacrificed for generality, or modularity for performance. Virtual memory page replacement schemes are an example of such a tradeoff. While the LRU page replacement policy rarely misbehaves grossly, it rarely provides optimal performance for any application. For some groups of applications we may suspect that a different pag...

A new formalism is given for read-modify-write (RMW) synchronization operations. This formalism is used to extend the memory reference combining mechanism, introduced in the NYU Ultracomputer, to arbitrary RMW operations. A formal correctness proof of this combining mechanism is given. General requirements for the practicality of combining are discussed. Combining is shown to be practical for many useful memory access operations. This includes memory updates of the form mem_val := mem_val op val, where op need not be associative, and a variety of synchronization primitives. The computation involved is shown to be closely related to parallel prefix evaluation. 1. INTRODUCTION Shared memory provides convenient communication between processes in a tightly coupled multiprocessing system. Shared variables can be used for data sharing, information transfer between processes, and, in particular, for coordination and synchronization. Constructs such as the semaphore introduced by Dijkstra in ...

: This paper considers a solution to the school timetabling problem. The timetabling problem involves scheduling a number of tuples, each consisting of class of students, a teacher, a subject and a room, to a fixed number of time slots. A Monte Carlo scheme called simulated annealing is used as an optimisation technique. The paper introduces the timetabling problem, and then describes the simulated annealing method. Annealing is then applied to the timetabling problem. A prototype timetabling environment is described followed by some experimental results. A parallel algorithm which can be implemented on a multiprocessor is presented. This algorithm can provide a faster solution than the equivalent sequential algorithm. Some further experimental results are given. 1 INTRODUCTION This paper considers a solution to the school timetabling problem. The timetabling problem involves scheduling a number of tuples, each consisting of class of students, a teacher, a subject and a room, to a fixe...

Ubiquitous computing promotes physical spaces with hundreds of specialized embedded devices that increase our productivity, alleviate some specific everyday tasks and provide new ways of interacting with the computational environment. Personal computers lose the focus of attention due to the fact that the computational environment is spread across the physical space. Therefore, the users ’ view of the computational environment is finally extended beyond the physical limits of the computer. Physical spaces become computer systems, or in other terms, Active Spaces. However, these Active Spaces require novel system software capable of seamlessly coordinating their hidden complexity. Our goal is to extend the model provided by current computer systems to allow interaction with physical spaces and their contained entities (physical and virtual) by means of a single abstraction called Active Space. 1.

Since the early days of logic programming, researchers in the field realized the potential for exploitation of parallelism present in the execution of logic programs. Their high-level nature, the presence of non-determinism, and their referential transparency, among other characteristics, make logic programs interesting candidates for obtaining speedups through parallel execution. At the same time, the fact that the typical applications of logic programming frequently involve irregular computations, make heavy use of dynamic data structures with logical variables, and involve search and speculation, makes the techniques used in the corresponding parallelizing compilers and run-time systems potentially interesting even outside the field. The objective of this paper is to provide a comprehensive survey of the issues arising in parallel execution of logic programming languages along with the most relevant approaches explored to date in the field. Focus is mostly given to the challenges emerging from the parallel execution of Prolog programs. The paper describes the major techniques used for shared memory implementation of Or-parallelism, And-parallelism, and combinations of the two. We also explore some related issues, such as memory

The notion of process equivalence of probabilistic processes is sensitive to the exact probabilities of transitions. Thus, a slight change in the transition probabilities will result in two equivalent processes being deemed no longer equivalent. This instability is due to the quantitative nature of probabilistic processes. In a situation where the process behaviour has a quantitative aspect there should be a more robust approach to process equivalence. This paper studies a metric between labelled Markov processes. This metric has the property that processes are at zero distance if and only if they are bisimilar. The metric is inspired by earlier work on logics for characterizing bisimulation and is related, in spirit, to the Hutchinson metric.

Abstract We study the following general online scheduling problem. Parallel jobs arrive dynamically according to the dependencies between them. Each job requests a certain number of processors with a specific communication configuration, but its running time is not known until it is completed. We present optimal online algorithms for PRAMs, hy\Lambda

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ion : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 30 3.1.3 Inheritance and Subclassing : : : : : : : : : : : : : : : : : : : : : : : : : : 32 3.1.4 Polymorphism : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 33 3.2 Definitions : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 36 3.2.1 Object-Oriented Language : : : : : : : : : : : : : : : : : : : : : : : : : : : 36 3.2.2 Object-Oriented System : : : : : : : : : : : : : : : : : : : : : : : : : : : : 37 3.3 Summary : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 38 4 Object-Oriented Operating Systems : : : : : : : : : : : : : : : : : : : : : : : : 40 4.1 Definition of an Object-Oriented Operating System : : : : : : : : : : : : : : : : : 40 4.2 Advantages of Object-Oriented Operating Systems : : : : : : : : : : : : : : : : : 43 4.2.1 Portability Advantages : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 43 4.2.2 Code Sharing Adv...

Although the typical process-layout manufacturing environment is susceptible to deadlocks, the problem of deadlock resolution in this context has only lately been undertaken by the scientific community. Previous studies have found that deadlock avoidance methodologies seem to be the most appropriate for this particular context. Unfortunately, in the general case, these methods suffer from high computational complexity which results in heuristic solutions and/or reduced performance. Taking the position that any solution to the problem should be scalable and provably correct, this paper proposes an analytical framework for designing deadlock avoidance policies for a subclass of Resource Allocation Systems (RAS). Specifically, this subclass is characterized by the fact that jobs in the system are defined by deterministic job-step sequences with every step in the sequence requiring a single unit of the system resources. Job-step models are appropriate for the study of the deadlo...