Fast Arrays: Atomic Arrays with Constant Time Initialization

Some algorithms require a large array, but only operate on a small fraction of its indices. Examples include adjacency matrices for sparse graphs, hash tables, and van Emde Boas trees. For such algorithms, array initialization can be the most time-consuming operation. Fast arrays were invented to avoid this costly initialization. A fast array is a software implementation of an array, such that the entire array can be initialized in just constant time. While algorithms for sequential fast arrays have been known for a long time, to the best of our knowledge, there are no previous algorithms for concurrent fast arrays. We present the first such algorithms in this paper. Our first algorithm is linearizable and wait-free, uses only linear space, and supports all operations - initialize, read, and write - in constant time. Our second algorithm enhances the first to additionally support all the read-modify-write operations available in hardware (such as compare-and-swap) in constant time

Space Tug systems study. Volume 2: Compendium

Possible storable propellant configurations and program plans are evaluated for the space tug. Alternatives examined include: use of existing expendable stages modified for use with shuttle, followed by a space tug at a later date; use of a modified growth version of existing expendable stages for greater performance and potential reuse, followed by a space tug at a later date; use of a low development cost, reusable, interim space tug available at shuttle initial operational capability (IOC) that could be evolved to greater system capabilities at a later date; and use a direct developed tug with maximum potential to be available at some specified time after space shuttle IOC. The capability options were narrowed down to three final options for detailed program definition

Non-reformist reform for Haskell Modularity

In this thesis, I present Backpack, a new language for building separately-typecheckable packages on top of a weak module system like Haskell’s. The design of Backpack is the first to bring the rich world of type systems to the practical world of packages via mixin modules. It’s inspired by the MixML module calculus of Rossberg and Dreyer but by choosing practicality over expressivity Backpack both simplifies that semantics and supports a flexible notion of applicative instantiation. Moreover, this design is motivated less by foundational concerns and more by the practical concern of integration into Haskell. The result is a new approach to writing modular software at the scale of packages.Modulsysteme wie die in Haskell erlauben nur eine weiche Art der Modularität, in dem Modulimplementierungen direkt von anderen Implementierungen abhängen und in dieser Abhängigkeitsreihenfolge verarbeitet werden müssen. Modulsysteme wie die in ML andererseits erlauben eine kräftige Art der Modularität, in dem explizite Schnittstellen Vermutungen über Abhängigkeiten ausdrücken und jeder Modultyp überprüft und unabhängig ergründet werden kann. In dieser Dissertation präsentiere ich Backpack, eine neue Sprache zur Entwicklung separattypenüberprüfbarer Pakete über einem weichen Modulsystem wie Haskells. Das Design von Backpack überführt erstmalig die reichhaltige Welt der Typsysteme in die praktische Welt der Pakete durch Mixin-Module. Es wird von der MixML-Kalkulation von Rossberg und Dreyer angeregt. Backpack vereinfacht allerdings diese Semantik durch die Auswahl von Anwendbarkeit statt Expressivität und fördert eine flexible Art von geeigneter Applicative- Instantiierung. Zudem wird dieses Design weniger von grundlegenden Anliegen als von dem praktischen Anliegen der Eingliederung in Haskell begründet. Die Semantik von Backpack wird durch die Ausarbeitung in Mengen von Haskell-Modulen und „binary interface files“ definiert, und zeigt so, wie Backpack Interoperabilität mit Haskell erhält, während Backpack es mit Schnittstellen nachrüstet. In meiner Formalisierung Backpacks präsentiere ich ein neuartiges Typsystem für Haskellmodule und überprüfe einen entscheidenen Korrektheitssatz, um die Semantik von Backpack zu validieren.Max Planck Institute for Software Systems (MPI-SWS

LIPIcs, Volume 248, ISAAC 2022, Complete Volume

LIPIcs, Volume 248, ISAAC 2022, Complete Volum

A Case Study Of Learning, Support And Disruption For Distance Learners In Student-Led Facebook Study Groups

This thesis reports on a qualitative investigation of learning in student-led Facebook module study groups, used by undergraduate distance learning students at a UK university. The study investigates the following issues: reasons why learners choose to use these study groups in social media; the types of learning taking place there; the nature of support there; and types of disruption experienced and its effect on student learning. The study uses a case study design to align with a constructivist, qualitative theoretical approach. Three data collection methods of participant interviews, documentary analysis of online group dialogue, and observation were used. This foregrounds the perspective of participants in various roles in these student-led groups, to prioritise student voice. The data was analysed in a thematic analysis, to identify latent and semantic themes. Many of the theory-led findings build on existing empirical research, and the explanatory concepts of connectivism, connected learning and the ethic of care are used to interpret the findings in more depth. Principal findings suggest learner experiences in Facebook module study groups converge around five themes of activity: community and relationships; academic subject learning; learning with others online; managing own learning; and difficulties and conflict. This analysis represents a typology of student activity that extends existing published empirical work, and is using the novel research context of student-led Facebook module study groups for distance learners. Types of learning that take place in the groups include the expedient acquisition of knowledge, practice of participation, and the development of digital skills. Study groups provide important relational and community supports to learners, and valued information. While Facebook also has the potential to disrupt student learning, diverse views were usually embraced constructively as an opportunity for skill development and critical thinking