An Optimised Flow for Futures: from Theory to Practice
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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. -
Ambient-Oriented Programming in Fractal
Ambient-Oriented Programming in Fractal AleˇsPlˇsek, Philippe Merle and Lionel Seinturier Project ADAM LIFL, INRIA-Futurs, Universit´edes Sciences et Technologies de Lille (USTL), FRANCE, { plsek | merle | seinturi }@lifl.fr Abstract. Ambient-Oriented Programming (AmOP) comprises a suite of challenges that are hard to meet by current software development techniques. Although Component-Oriented Programming (COP) repre- sents promising approach, the state-of-the-art component models do not provide sufficient adaptability towards specific constraints of the Ambi- ent field. In this position paper we argue that merging AmOP and COP can be achieved by introducing the Fractal component model and its new feature : Component-Based Controlling Membranes. The proposed solution allows dynamical adaptation of component systems towards the challenges of the Ambient world. 1 Introduction Ambient-Oriented Programming (AmOP) [1] as a new trend in software devel- opment comprises a suite of challenges which are yet to be addressed fully. So far, only a few solutions facing the obstacles of ambient programming have been developed. In this paper we focus on AmbientTalk [1] since in our opinion it represents one of the most sophisticated solutions. Although AmbientTalk conceptually proposes a way to implement applica- tions for the ambient environment, this is achieved by defining a new program- ming language. Consequently, AmbientTalk potentially introduces a steep learn- ing curve for the developers. From this point of view, it is reasonable to search for an approach which uses well-known techniques and is powerful enough to face the obstacles of ambient programming. We believe that these requirements can be met by the introduction of Component-Based Software Engineering techniques. -
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. -
Ambient-Oriented Programming in Ambienttalk
Ambient-Oriented Programming in AmbientTalk Jessie Dedecker?, Tom Van Cutsem?, Stijn Mostinckx??, Theo D’Hondt, and Wolfgang De Meuter jededeck | tvcutsem | smostinc | tjdhondt | [email protected] Programming Technology Laboratory Vrije Universiteit Brussel, Belgium Abstract. A new field in distributed computing, called Ambient Intel- ligence, has emerged as a consequence of the increasing availability of wireless devices and the mobile networks they induce. Developing soft- ware for mobile networks is extremely hard in conventional programming languages because the network is dynamically demarcated. This leads us to postulate a suite of characteristics of future Ambient-Oriented Pro- gramming languages. A simple reflective programming language, called AmbientTalk, that meets the characteristics is presented. It is validated by implementing a collection of high level language features that are used in the implementation of an ambient messenger application . 1 Introduction Software development for mobile devices is given a new impetus with the advent of mobile networks. Mobile networks surround a mobile device equipped with wireless technology and are demarcated dynamically as users move about. Mo- bile networks turn isolated applications into cooperative ones that interact with their environment. This vision of ubiquitous computing, originally described by Weiser [38], has recently been termed Ambient Intelligence (AmI for short) by the European Council’s IST Advisory Group [12]. Mobile networks that surround a device have several properties that distin- guish them from other types of networks. The most important ones are that connections are volatile (because the communication range of wireless technol- ogy is limited) and that the network is open (because devices can appear and disappear unheraldedly). -
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. -
Concepts and Paradigms of Object-Oriented Programming Expansion of Oct 400PSLA-89 Keynote Talk Peter Wegner, Brown University
Concepts and Paradigms of Object-Oriented Programming Expansion of Oct 400PSLA-89 Keynote Talk Peter Wegner, Brown University 1. What Is It? 8 1.1. Objects 8 1.2. Classes 10 1.3. Inheritance 11 1.4. Object-Oriented Systems 12 2. What Are Its Goals? 13 2.1. Software Components 13 2.2. Object-Oriented Libraries 14 2.3. Reusability and Capital-intensive Software Technology 16 2.4. Object-Oriented Programming in the Very Large 18 3. What Are Its Origins? 19 3.1. Programming Language Evolution 19 3.2. Programming Language Paradigms 21 4. What Are Its Paradigms? 22 4.1. The State Partitioning Paradigm 23 4.2. State Transition, Communication, and Classification Paradigms 24 4.3. Subparadigms of Object-Based Programming 26 5. What Are Its Design Alternatives? 28 5.1. Objects 28 5.2. Types 33 5.3. Inheritance 36 5.4. Strongly Typed Object-Oriented Languages 43 5.5. Interesting Language Classes 45 5.6. Object-Oriented Concept Hierarchies 46 6. what Are Its Models of Concurrency? 49 6.1. Process Structure 50 6.2. Internal Process Concurrency 55 6.3. Design Alternatives for Synchronization 56 6.4. Asynchronous Messages, Futures, and Promises 57 6.5. Inter-Process Communication 58 6.6. Abstraction, Distribution, and Synchronization Boundaries 59 6.7. Persistence and Transactions 60 7. What Are Its Formal Computational Models? 62 7.1. Automata as Models of Object Behavior 62 7.2. Mathematical Models of Types and Classes 65 7.3. The Essence of Inheritance 74 7.4. Reflection in Object-Oriented Systems 78 8. -