PolyAPM: Vergleichende Parallelprogrammierung mit Abstrakten Parallelen Maschinen

A parallelising compilation consists of many translation and optimisation stages. The programmer may steer the compiler through these stages by supplying directives with the source code or setting compiler switches. However, for an evaluation of the effects of individual stages, their selection and their best order, this approach is not optimal. To solve this problem, we propose the following method. The compilation is cast as a sequence of program transformations. Each intermediate program runs on an Abstract Parallel Machine (APM), while the program generated by the final transformation runs on the target architecture. Our intermediate programs are all in the same language, Haskell. Thus, each program is executable and still abstract enough to be legible, which enables the evaluation of the transformation that generated it. This evaluation is supported by a cost model, which makes a performance prediction of the abstract program for a real machine. Our project, PolyAPM, provides an acyclic directed graph -- usually a tree -- of APMs whose traversal specifies different combinations and orders of transformations. From one source program, several target programs can be constructed. Their run time characteristics can be evaluated and compared. The goal of PolyAPM is not to support the one-off construction of parallel application programs. For the method's overhead to pay off, the project aims rather at supporting the construction and comparison of many similar variations of a parallel program and a comparative evaluation of parallelisation techniques. With the automation of transformations, PolyAPM can also be used to construct semi-automatic compilation systems.Eine parallelisierende Compilation besteht aus vielen Übersetzungs- und Optimierungsstufen. Der Programmierer kann den Compiler in diesen Stufen steuern, in dem er im Quellcode Anweisungen einfügt oder Compileroptionen verwendet. Für eine Bewertung der Auswirkungen der einzelnen Stufen, der Auswahl der Stufen und ihrer besten Reihenfolge ist der Ansatz aber nicht geeignet. Um dieses Problem zu lösen, schlagen wir folgende Methode vor. Eine Compilation wird als Abfolge von Programmtransformationen betrachtet. Jedes Zwischenprogramm gehört jeweils zu einer Abstrakten Parallelen Maschine (APM), während das durch die letzte Transformation erzeugte Program für die Zielarchitektur bestimmt ist. Alle Zwischenprogramme sind in der Sprache Haskell geschrieben. Dadurch ist jedes Programm ausführbar und trotzdem abstrakt genug, um gut lesbar zu sein. Durch diese Ausführbarkeit kann die Transformation, durch die das Programm erzeugt wird, bewertet werden. Diese Bewertung wird durch ein Kostenmodell unterstützt, das eine Performance-Vorhersage des abstrakten Programms, bezogen auf eine reale Maschine, ermöglicht. Unser Projekt PolyAPM liefert einen azyklischen, gerichteten Graphen - in der Regel einen Baum - aus APMs, dessen Traversierungen jeweils bestimmte Kombinationen und Reihenfolgen von Transformationen definieren. Aus einem Quellprogramm können verschiedene Zielprogramme erzeugt werden, deren Laufzeitverhalten bewert- und vergleichbar ist. Das Ziel von PolyAPM liegt nicht in der Erzeugung eines einzelnen, parallelen Programms. Damit sich der zusätzliche Aufwand der Methode auszahlt, richtet sich das Projekt eher auf die Entwicklung und den Vergleich vieler, ähnlicher Variationen eines parallelen Programms und der vergleichenden Bewertung von Parallelisierungstechniken. Mit der Automatisierung von Transformationen kann PolyAPM dazu benutzt werden, halbautomatische Compilations-Systeme zu bauen

Volunteer computing

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (p. 205-216).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.This thesis presents the idea of volunteer computing, which allows high-performance parallel computing networks to be formed easily, quickly, and inexpensively by enabling ordinary Internet users to share their computers' idle processing power without needing expert help. In recent years, projects such as SETI@home have demonstrated the great potential power of volunteer computing. In this thesis, we identify volunteer computing's further potentials, and show how these can be achieved. We present the Bayanihan system for web-based volunteer computing. Using Java applets, Bayanihan enables users to volunteer their computers by simply visiting a web page. This makes it possible to set up parallel computing networks in a matter of minutes compared to the hours, days, or weeks required by traditional NOW and metacomputing systems. At the same time, Bayanihan provides a flexible object-oriented software framework that makes it easy for programmers to write various applications, and for researchers to address issues such as adaptive parallelism, fault-tolerance, and scalability. Using Bayanihan, we develop a general-purpose runtime system and APIs, and show how volunteer computing's usefulness extends beyond solving esoteric mathematical problems to other, more practical, master-worker applications such as image rendering, distributed web-crawling, genetic algorithms, parametric analysis, and Monte Carlo simulations. By presenting a new API using the bulk synchronous parallel (BSP) model, we further show that contrary to popular belief and practice, volunteer computing need not be limited to master-worker applications, but can be used for coarse-grain message-passing programs as well. Finally, we address the new problem of maintaining reliability in the presence of malicious volunteers. We present and analyze traditional techniques such as voting, and new ones such as spot-checking, encrypted computation, and periodic obfuscation. Then, we show how these can be integrated in a new idea called credibility-based fault-tolerance, which uses probability estimates to limit and direct the use of redundancy. We validate this new idea with parallel Monte Carlo simulations, and show how it can achieve error rates several orders-of-magnitude smaller than traditional voting for the same slowdown.by Luis F.G. Sarmenta.Ph.D

Computer Aided Verification

This open access two-volume set LNCS 13371 and 13372 constitutes the refereed proceedings of the 34rd International Conference on Computer Aided Verification, CAV 2022, which was held in Haifa, Israel, in August 2022. The 40 full papers presented together with 9 tool papers and 2 case studies were carefully reviewed and selected from 209 submissions. The papers were organized in the following topical sections: Part I: Invited papers; formal methods for probabilistic programs; formal methods for neural networks; software Verification and model checking; hyperproperties and security; formal methods for hardware, cyber-physical, and hybrid systems. Part II: Probabilistic techniques; automata and logic; deductive verification and decision procedures; machine learning; synthesis and concurrency. This is an open access book

Information management in professional organisations: Alternative approaches to the application of information systems in professional organisations

This research aims to examine the influence of the use of information technology on professional organisations and to identify which policies could be followed by the management of such organisations to apply information systems. Traditional approaches to information technology assume that organisations operate as 'machine bureaucracies' - a top down management style, standardisation of work processes and a high level of interdependency amongst departments. Such assumptions are not relevant to professional organisations. In these organisations professionals perform and control the primary process of the organisation in close interaction with their clients and with a high level of autonomy. With the rise of computers and information technology, such organisations are confronted with the question of how to apply this technology, since conventional models may not be appropriate. The strategy used to accomplish the research objectives was the case study methodology, complemented by a literature study. Two hospitals were chosen as case sites, since hospitals are generally perceived as typical examples of professional organisations which make intensive use of information technology. Interviews and conversations with personnel, observations and hospital documents were the main sources for the case studies. This research indicates that four general strategies can be followed which are captured in a model which is developed throughout this study namely the Professional - Heteronomy model. First, information technology can be utilised by making the support activities more efficient, e.g. by using computers for administration and other office activities, without affecting the professionals directly with such technology [this may imply that professionals develop and use their own information systems relatively autonomously]. Second, information technology can be used for the direct support of professional activities. In this case, the primary goal is to motivate professionals and to help them to improve their work and their level of professionalisation. A third direction might be to use this technology with the objective of substituting professionals by computers, thus reducing the number of professionals needed. Cutting costs or improving services are management motives for introducing such a policy. The fourth direction is to use information technology for management support. This can be practised by deriving management information from data gathered from the primary process. The management may obtain the information to manage and to control the organisation in a more direct and tight way through these systems. A major conclusion is that the states of computing management model (Kraemer et al., 1989) is a useful framework to categorise the state of computing in professional organisations, as well as being a tool to model changes of these states. The study proposes some adaptations to this model in order to make it more refined: in the adapted version the model can reflect several states at the same time. This will be a more realistic representation of computing in many cases. This study also observed in both case study sites what we term multiformity in computing: in other words, various actors influenced decision making with respect to information systems in apparently contrasting ways. The study proposes that a more conscious management of 'multiform computing' may be a more realistic alternative to the uniform approaches which are common

Towards building a theory of Lean implementation in healthcare

Includes bibliographical references.Lean, a management system based on the Toyota Production System, is increasingly being applied to healthcare contexts with mixed outcomes. While there are many case studies reporting on the outcomes of Lean implementation, there is little empirical evidence indicating which factors influence Lean implementation. Furthermore, there is an absence of critical and theory building research of Lean implementation. This study specifically addressed these gaps by identifying some of the enablers and inhibitors of Lean implementation, using empirical methods

Scalable String and Suffix Sorting: Algorithms, Techniques, and Tools

This dissertation focuses on two fundamental sorting problems: string sorting and suffix sorting. The first part considers parallel string sorting on shared-memory multi-core machines, the second part external memory suffix sorting using the induced sorting principle, and the third part distributed external memory suffix sorting with a new distributed algorithmic big data framework named Thrill.Comment: 396 pages, dissertation, Karlsruher Instituts f\"ur Technologie (2018). arXiv admin note: text overlap with arXiv:1101.3448 by other author