Concepts and Paradigms of Object-Oriented Programming Expansion of Oct 400PSLA-89 Keynote Talk Peter Wegner, Brown University
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Composable Concurrency Models
Composable Concurrency Models Dan Stelljes Division of Science and Mathematics University of Minnesota, Morris Morris, Minnesota, USA 56267 [email protected] ABSTRACT Given that an application is likely to make use of more The need to manage concurrent operations in applications than one concurrency model, programmers would prefer that has led to the development of a variety of concurrency mod- different types of models could safely interact. However, dif- els. Modern programming languages generally provide sev- ferent models do not necessarily work well together, nor are eral concurrency models to serve different requirements, and they designed to. Recent work has attempted to identify programmers benefit from being able to use them in tandem. common \building blocks" that could be used to compose We discuss challenges surrounding concurrent programming a variety of models, possibly eliminating subtle problems and examine situations in which conflicts between models when different models interact and allowing models to be can occur. Additionally, we describe attempts to identify represented at lower levels without resorting to rough ap- features of common concurrency models and develop lower- proximations [9, 11, 12]. level abstractions capable of supporting a variety of models. 2. BACKGROUND 1. INTRODUCTION In a concurrent program, the history of operations may Most interactive computer programs depend on concur- not be the same for every execution. An entirely sequen- rency, the ability to perform different tasks at the same tial program could be proved to be correct by showing that time. A web browser, for instance, might at any point be its history (that is, the sequence in which its operations are rendering documents in multiple tabs, transferring files, and performed) always yields a correct result. -
Reactive Async: Expressive Deterministic Concurrency
Reactive Async: Expressive Deterministic Concurrency Philipp Haller Simon Geries Michael Eichberg Guido Salvaneschi KTH Royal Institute of Technology, Sweden TU Darmstadt, Germany [email protected] feichberg, [email protected] Abstract tion can generate non-deterministic results because of their Concurrent programming is infamous for its difficulty. An unpredictable scheduling. Traditionally, developers address important source of difficulty is non-determinism, stemming these problems by protecting state from concurrent access from unpredictable interleavings of concurrent activities. via synchronisation. Yet, concurrent programming remains Futures and promises are widely-used abstractions that help an art: insufficient synchronisation leads to unsound pro- designing deterministic concurrent programs, although this grams but synchronising too much does not exploit hardware property cannot be guaranteed statically in mainstream pro- capabilities effectively for parallel execution. gramming languages. Deterministic-by-construction con- Over the years researchers have proposed concurrency current programming models avoid this issue, but they typi- models that attempt to overcome these issues. For exam- cally restrict expressiveness in important ways. ple the actor model [13] encapsulates state into actors This paper introduces a concurrent programming model, which communicate via asynchronous messages–a solution Reactive Async, which decouples concurrent computations that avoids shared state and hence (low-level) race condi- using -
A Reduction Semantics for Direct-Style Asynchronous Observables
Journal of Logical and Algebraic Methods in Programming 105 (2019) 75–111 Contents lists available at ScienceDirect Journal of Logical and Algebraic Methods in Programming www.elsevier.com/locate/jlamp A reduction semantics for direct-style asynchronous observables ∗ Philipp Haller a, , Heather Miller b a KTH Royal Institute of Technology, Sweden b Carnegie Mellon University, USA a r t i c l e i n f o a b s t r a c t Article history: Asynchronous programming has gained in importance, not only due to hardware develop- Received 31 January 2016 ments like multi-core processors, but also due to pervasive asynchronicity in client-side Received in revised form 6 March 2019 Web programming and large-scale Web applications. However, asynchronous program- Accepted 6 March 2019 ming is challenging. For example, control-flow management and error handling are much Available online 18 March 2019 more complex in an asynchronous than a synchronous context. Programming with asyn- chronous event streams is especially difficult: expressing asynchronous stream producers and consumers requires explicit state machines in continuation-passing style when using widely-used languages like Java. In order to address this challenge, recent language designs like Google’s Dart introduce asynchronous generators which allow expressing complex asynchronous programs in a familiar blocking style while using efficient non-blocking concurrency control under the hood. However, several issues remain unresolved, including the integration of analogous constructs into statically-typed languages, and the formalization and proof of important correctness properties. This paper presents a design for asynchronous stream generators for Scala, thereby ex- tending previous facilities for asynchronous programming in Scala from tasks/futures to asynchronous streams. -
Abstract Interface Behavior of an Object-Oriented Language with Futures and Promises
Abstract interface behavior of an object-oriented language with futures and promises 3. September 2007 Erika Abrah´ am´ 1, and Immo Grabe2, and Andreas Gruner¨ 2, and Martin Steffen3 1 Albert-Ludwigs-University Freiburg, Germany 2 Christian-Albrechts-University Kiel, Germany 3 University of Oslo, Norway 1 Motivation How to marry concurrency and object-orientation has been a long-standing issue; see e.g., [2] for an early discussion of different design choices. Recently, the thread-based model of concurrency, prominently represented by languages like Java and C# has been criticized, especially in the context of component-based software development. As the word indicates, components are (software) artifacts intended for composition, i.e., open systems, interacting with a surrounding environment. To compare different concurrency models on a solid mathematical basis, a semantical description of the interface behavior is needed, and this is what we do in this work. We present an open semantics for a core of the Creol language [4,7], an object-oriented, concurrent language, featuring in particular asynchronous method calls and (since recently [5]) future-based concurrency. Futures and promises A future, very generally, represents a result yet to be computed. It acts as a proxy for, or reference to, the delayed result from a given sequential piece of code (e.g., a method or a function body in an object-oriented, resp. a functional setting). As the client of the delayed result can proceed its own execution until it actually needs the result, futures provide a natural, lightweight, and (in a functional setting) transparent mechanism to introduce parallelism into a language. -
N4244: Resumable Lambdas
Document Number: N4244 Date: 2014-10-13 Reply To Christopher Kohlhoff <[email protected]> Resumable Lambdas: A language extension for generators and coroutines 1 Introduction N3977 Resumable Functions and successor describe a language extension for resumable functions, or “stackless” coroutines. The earlier revision, N3858, states that the motivation is: [...] the increasing importance of efficiently handling I/O in its various forms and the complexities programmers are faced with using existing language features and existing libraries. In contrast to “stackful” coroutines, a prime use case for stackless coroutines is in server applications that handle many thousands or millions of clients. This is due to stackless coroutines having lower memory requirements than stackful coroutines, as the latter, like true threads, must have a reserved stack space. Memory cost per byte is dropping over time, but with server applications at this scale, per-machine costs, such as hardware, rack space, network connectivity and administration, are significant. For a given request volume, it is always cheaper if the application can be run on fewer machines. Existing best practice for stackless coroutines in C and C++ uses macros and a switch-based technique similar to Duff’s Device. Examples include the coroutine class included in Boost.Asio1, and Protothreads2. Simon Tatham’s web page3, Coroutines in C, inspired both of these implementations. A typical coroutine using this model looks like this: void operator()(error_code ec, size_t n) { if (!ec) reenter (this) { for (;;) { yield socket_->async_read_some(buffer(*data_), *this); yield async_write(*socket_, buffer(*data_, n), *this); } } } The memory overhead of a stackless coroutine can be as low as a single int. -
The Interactive Nature of Computing: Refuting the Strong Church-Turing Thesis
TEX source file Click here to download Manuscript: paper.tex The Interactive Nature of Computing: Refuting the Strong Church-Turing Thesis Dina Goldin∗, Peter Wegner Brown University Abstract. The classical view of computing positions computation as a closed-box transformation of inputs (rational numbers or finite strings) to outputs. According to the interactive view of computing, computation is an ongoing interactive process rather than a function-based transformation of an input to an output. Specifi- cally, communication with the outside world happens during the computation, not before or after it. This approach radically changes our understanding of what is computation and how it is modeled. The acceptance of interaction as a new paradigm is hindered by the Strong Church-Turing Thesis (SCT), the widespread belief that Turing Machines (TMs) capture all computation, so models of computation more expressive than TMs are impossible. In this paper, we show that SCT reinterprets the original Church-Turing Thesis (CTT) in a way that Turing never intended; its commonly assumed equiva- lence to the original is a myth. We identify and analyze the historical reasons for the widespread belief in SCT. Only by accepting that it is false can we begin to adopt interaction as an alternative paradigm of computation. We present Persistent Turing Machines (PTMs), that extend TMs to capture sequential interaction. PTMs allow us to formulate the Sequential Interaction Thesis, going beyond the expressiveness of TMs and of the CTT. The paradigm shift to interaction provides an alternative understanding of the nature of computing that better reflects the services provided by today’s computing technology. -
Introduction to the Literature on Programming Language Design Gary T
Computer Science Technical Reports Computer Science 7-1999 Introduction to the Literature On Programming Language Design Gary T. Leavens Iowa State University Follow this and additional works at: http://lib.dr.iastate.edu/cs_techreports Part of the Programming Languages and Compilers Commons Recommended Citation Leavens, Gary T., "Introduction to the Literature On Programming Language Design" (1999). Computer Science Technical Reports. 59. http://lib.dr.iastate.edu/cs_techreports/59 This Article is brought to you for free and open access by the Computer Science at Iowa State University Digital Repository. It has been accepted for inclusion in Computer Science Technical Reports by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Introduction to the Literature On Programming Language Design Abstract This is an introduction to the literature on programming language design and related topics. It is intended to cite the most important work, and to provide a place for students to start a literature search. Keywords programming languages, semantics, type systems, polymorphism, type theory, data abstraction, functional programming, object-oriented programming, logic programming, declarative programming, parallel and distributed programming languages Disciplines Programming Languages and Compilers This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/cs_techreports/59 Intro duction to the Literature On Programming Language Design Gary T. Leavens TR 93-01c Jan. 1993, revised Jan. 1994, Feb. 1996, and July 1999 Keywords: programming languages, semantics, typ e systems, p olymorphism, typ e theory, data abstrac- tion, functional programming, ob ject-oriented programming, logic programming, declarative programming, parallel and distributed programming languages. -
Dina Goldin · Scott A. Smolka · Peter Wegner (Eds.) Dina Goldin Scott A
Dina Goldin · Scott A. Smolka · Peter Wegner (Eds.) Dina Goldin Scott A. Smolka Peter Wegner (Eds.) Interactive Computation The New Paradigm With 84 Figures 123 Editors Dina Goldin Scott A. Smolka Brown University State University of New York at Stony Brook Computer Science Department Department of Computer Science Providence, RI 02912 Stony Brook, NY 11794-4400 USA USA [email protected] [email protected] Peter Wegner Brown University Computer Science Department Providence, RI 02912 USA [email protected] Cover illustration: M.C. Escher’s „Whirlpools“ © 2006 The M.C. Escher Company-Holland. All rights reserved. www.mcescher.com Library of Congress Control Number: 2006932390 ACM Computing Classification (1998): F, D.1, H.1, H.5.2 ISBN-10 3-540-34666-X Springer Berlin Heidelberg New York ISBN-13 978-3-540-34666-1 Springer Berlin Heidelberg New York This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broad- casting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable for prosecution under the German Copyright Law. Springer is a part of Springer Science+Business Media springer.com © Springer-Verlag Berlin Heidelberg 2006 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant pro- tective laws and regulations and therefore free for general use. -
From Events to Futures and Promises and Back
From Events to Futures and Promises and back Martin Sulzmann Faculty of Computer Science and Business Information Systems Karlsruhe University of Applied Sciences Moltkestrasse 30, 76133 Karlsruhe, Germany [email protected] Abstract. Events based on channel communications and futures/promises are powerful but seemingly different concepts for concurrent program- ming. We show that one concept can be expressed in terms of the other with surprisingly little effort. Our results offer light-weight library based approaches to implement events and futures/promises. Empirical results show that our approach works well in practice. 1 Introduction There exists a wealth of programming models to make concurrent programming easier. A popular form is Communicating Sequential Processes (CSP) [7] which has found its way into several programming languages in one form or another. For example, Haskell [9] provides native support for a primitive channel type called MVar which is effectively a buffered channel of size one. The Go pro- gramming language [5] follows more closely CSP and has native support for synchronous channel-based message passing and selective communication. Con- current ML (CML) [11] provides for even richer abstractions in the form of events. Another popular concurrency approach is the concept of futures/promises [1, 4]. For example, Alice [12] provides native support for futures/promises whereas Scala [6] follows a library-based approach and provides a powerful set of combi- nators to compose futures/promises. Our interest lies in establishing some connections among channel-based events and futures/promises by expressing one concept in terms of the other. This is interesting and helpful for several reasons. -
Integrating Rx and Async for Direct-Style Reactive Streams
RAY: Integrating Rx and Async for Direct-Style Reactive Streams Philipp Haller Heather Miller Typesafe, Inc. EPFL [email protected] heather.miller@epfl.ch ABSTRACT (it's even possible for a stream to never complete.) Given Languages like F#, C#, and recently also Scala, provide the richer substrate of reactive streams, the Async model \async" extensions which aim to make asynchronous pro- has to be generalized in several dimensions. gramming easier by avoiding an inversion of control that is inherent in traditional callback-based programming models We call our model RAY, inspired by its main constructs, (for the purpose of this paper called the \Async" model). rasync, await, yield, introduced later in the paper. This paper outlines a novel approach to integrate the Async model with observable streams of the Reactive Extensions This paper makes the following contributions: model which is best-known from the .NET platform, and of which popular implementations exist for Java, Ruby, and • A design of a new programming model, RAY, which in- other widespread languages. We outline the translation of tegrates the Async model and the Reactive Extensions \Reactive Async" programs to efficient state machines, in a model in the context of the Scala Async project [5] (pro- way that generalizes the state machine translation of regular posed for adoption in mainline Scala [6]); Async programs. Finally, we sketch a formalization of the Reactive Async model in terms of a small-step operational • An operational semantics of the proposed program- semantics. ming model. Our operational semantics extends the formal model presented in [1] for C#'s async/await to 1. -
A Bibliography of Publications of Alan Mathison Turing
A Bibliography of Publications of Alan Mathison Turing Nelson H. F. Beebe University of Utah Department of Mathematics, 110 LCB 155 S 1400 E RM 233 Salt Lake City, UT 84112-0090 USA Tel: +1 801 581 5254 FAX: +1 801 581 4148 E-mail: [email protected], [email protected], [email protected] (Internet) WWW URL: http://www.math.utah.edu/~beebe/ 24 August 2021 Version 1.227 Abstract This bibliography records publications of Alan Mathison Turing (1912– 1954). Title word cross-reference 0(z) [Fef95]. $1 [Fis15, CAC14b]. 1 [PSS11, WWG12]. $139.99 [Ano20]. $16.95 [Sal12]. $16.96 [Kru05]. $17.95 [Hai16]. $19.99 [Jon17]. 2 [Fai10b]. $21.95 [Sal12]. $22.50 [LH83]. $24.00/$34 [Kru05]. $24.95 [Sal12, Ano04, Kru05]. $25.95 [KP02]. $26.95 [Kru05]. $29.95 [Ano20, CK12b]. 3 [Ano11c]. $54.00 [Kru05]. $69.95 [Kru05]. $75.00 [Jon17, Kru05]. $9.95 [CK02]. H [Wri16]. λ [Tur37a]. λ − K [Tur37c]. M [Wri16]. p [Tur37c]. × [Jon17]. -computably [Fai10b]. -conversion [Tur37c]. -D [WWG12]. -definability [Tur37a]. -function [Tur37c]. 1 2 . [Nic17]. Zycie˙ [Hod02b]. 0-19-825079-7 [Hod06a]. 0-19-825080-0 [Hod06a]. 0-19-853741-7 [Rus89]. 1 [Ano12g]. 1-84046-250-7 [CK02]. 100 [Ano20, FB17, Gin19]. 10011-4211 [Kru05]. 10th [Ano51]. 11th [Ano51]. 12th [Ano51]. 1942 [Tur42b]. 1945 [TDCKW84]. 1947 [CV13b, Tur47, Tur95a]. 1949 [Ano49]. 1950s [Ell19]. 1951 [Ano51]. 1988 [Man90]. 1995 [Fef99]. 2 [DH10]. 2.0 [Wat12o]. 20 [CV13b]. 2001 [Don01a]. 2002 [Wel02]. 2003 [Kov03]. 2004 [Pip04]. 2005 [Bro05]. 2006 [Mai06, Mai07]. 2008 [Wil10]. 2011 [Str11]. 2012 [Gol12]. 20th [Kru05]. 25th [TDCKW84]. -
LEAGER PROGRAMMING Abstract
LEAGER PROGRAMMING Anthony Chyr UUCS-19-002 School of Computing University of Utah Salt Lake City, UT 84112 USA February 26, 2019 Abstract Leager programming, a portmanteau of “lazy” and “eager” or “limit” and “eager,” is an evaluation strategy that mixes lazy evaluation and eager evaluation. This evaluation strategy allows iterators to precompute the next value in a separate thread, storing the result in a cache until it is needed by the caller. Leager programming often takes the form of an iterator, which alone allows data to be prefetched, and when chained together can be used to form concurrent pipelines. We found a dramatic reduction in latency on par with code written with asynchronous callbacks, while making minimal modifications to the initial sequential code. LEAGER PROGRAMMING by Anthony Chyr A senior thesis submitted to the faculty of The University of Utah in partial fulfillment of the requirements for the degree of Bachelor of Computer Science School of Computing The University of Utah May 2019 Approved: / / Matthew Flatt H. James de St. Germain Supervisor Director of Undergraduate Studies School of Computing / Ross Whitaker Diretor School of Computing Copyright c Anthony Chyr 2019 All Rights Reserved ABSTRACT Leager programming, a portmanteau of “lazy” and “eager” or “limit” and “eager,” is an evaluation strategy that mixes lazy evaluation and eager evaluation. This evaluation strategy allows iterators to precompute the next value in a separate thread, storing the result in a cache until it is needed by the caller. Leager programming often takes the form of an iterator, which alone allows data to be prefetched, and when chained together can be used to form concurrent pipelines.