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Efficient and Thread-Safe objects for Dynamically-Typed languages

acm sigplan NOTICES 2016年第10期51卷 642-659页

作者： Daloze, Benoit Marr, Stefan Bonetta, Daniele Moessenboeck, Hanspeter Johannes Kepler Univ Linz Linz Austria Oracle Labs Linz Austria

We are in the multi-core era. Dynamically-typed languages are in widespread use, but their support for multithreading still lags behind. One of the reasons is that the sophisticated techniques they use to efficiently represent their dynamic object models are often unsafe in multithreaded environments. This paper defines safety requirements for dynamic object models in multithreaded environments. Based on these requirements, a language-agnostic and thread-safe object model is designed that maintains the efficiency of sequential approaches. This is achieved by ensuring that field reads do not require synchronization and field updates only need to synchronize on objects shared between threads. Basing our work on JRuby+Truffle, we show that our safe object model has zero overhead on peak performance for thread-local objects and only 3% average overhead on parallel benchmarks where field updates require synchronization. Thus, it can be a foundation for safe and efficient multithreaded VMs for a wide range of dynamic languages.

关键词： Dynamically-sized objects Dynamic languages Concurrency Virtual Machine Java Truffle Graal Ruby

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Computing Repair Alternatives for Malformed Programs using Constraint Attribute Grammars

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acm sigplan NOTICES 2016年第10期51卷 711-730页

作者： Steimann, Friedrich Hagemann, Joerg Ulke, Bastian Fernuniv Lehrgebiet Programmiersyst Hagen Germany

Attribute grammars decorate the nodes of a program's parse tree with attributes whose values are defined by equations encoding the (static) semantics of a programming language. We show how replacing the equations of an attribute grammar with equivalent constraints that can be solved by a constraint solver allows us to compute repairs of a malformed program solely from a specification that was originally designed for checking its well-formedness. We present two repair modes - shallow and deep fixing - whose computed repair alternatives are guaranteed to repair every error on which they are invoked. While shallow fixing may introduce new errors, deep fixing never does;to make it tractable, we implement it using neighborhood search. We demonstrate the feasibility of our approach by implementing it on top of ExtendJ, an attribute grammar based Java compiler, and by applying it to an example from the Java EE context, detecting and fixing well-formedness errors (both real and injected) in a body of 14 open-source subject programs.

关键词： attribute grammars constraints repair languages Algorithms

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Type Inference for Static Compilation of JavaScript

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acm sigplan NOTICES 2016年第10期51卷 410-429页

作者： Chandra, Satish Gordon, Colin S. Jeannin, Jean-Baptiste Schlesinger, Cole Sridharan, Manu Tip, Frank Choi, Youngil Samsung Res Amer Mountain View CA 94043 USA Drexel Univ Philadelphia PA 19104 USA Northeastern Univ Boston MA 02115 USA Samsung Elect Suwon South Korea

We present a type system and inference algorithm for a rich subset of JavaScript equipped with objects, structural subtyping, prototype inheritance, and first-class methods. The type system supports abstract and recursive objects, and is expressive enough to accommodate several standard benchmarks with only minor workarounds. The invariants enforced by the types enable an ahead-of-time compiler to carry out optimizations typically beyond the reach of static compilers for dynamic languages. Unlike previous inference techniques for prototype inheritance, our algorithm uses a combination of lower and upper bound propagation to infer types and discover type errors in all code, including uninvoked functions. The inference is expressed in a simple constraint language, designed to leverage off-the-shelf fixed point solvers. We prove soundness for both the type system and inference algorithm. An experimental evaluation showed that the inference is powerful, handling the aforementioned benchmarks with no manual type annotation, and that the inferred types enable effective static compilation.

关键词： object-oriented type systems type inference JavaScript

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SPLASH Indianapolis 2013: OOPSLA 2013 - Proceedings of the 2013 international conference on object oriented programming systems languages and Applications

SPLASH Indianapolis 2013: OOPSLA 2013 - Proceedings of the 2...

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2013 28th acm sigplan conference on object-oriented programming, systems, languages, and Applications, OOPSLA 2013

ISBN: (纸本)9781450323741

The proceedings contain 50 papers. The topics discussed include: empirical analysis of programming language adoption;steering symbolic execution to less traveled paths;verifying quantitative reliability for programs that execute on unreliable hardware;miniboxing: improving the speed to code size tradeoff in parametric polymorphism translations;taking off the gloves with reference counting immix;resurrector: a tunable object lifetime profiling technique for optimizing real-world programs;effective race detection for event-driven programs;storage strategies for collections in dynamically typed languages;instant pickles: generating object-oriented pickler combinators for fast and extensible serialization;interacting with dead objects;and python: the full Monty: a tested semantics for the python programming language.

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Semantics-Based Program Verifiers for All languages

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acm sigplan NOTICES 2016年第10期51卷 74-91页

作者： Stefanescu, Andrei Park, Daejun Yuwen, Shijiao Li, Yilong Rosu, Grigore Univ Illinois Urbana IL 61801 USA Runtime Verificat Inc Urbana IL USA

We present a language-independent verification framework that can be instantiated with an operational semantics to automatically generate a program verifier. The framework treats both the operational semantics and the program correctness specifications as reachability rules between matching logic patterns, and uses the sound and relatively complete reachability logic proof system to prove the specifications using the semantics. We instantiate the framework with the semantics of one academic language, KERNELC, as well as with three recent semantics of real-world languages, C, JAVA, and JAVASCRIPT, developed independently of our verification infrastructure. We evaluate our approach empirically and show that the generated program verifiers can check automatically the full functional correctness of challenging heap-manipulating programs implementing operations on list and tree data structures, like AVL trees. This is the first approach that can turn the operational semantics of real-world languages into correct-by-construction automatic verifiers.

关键词： reachability logic matching logic K framework languages Theory Verification

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GEMS: Shared-Memory Parallel programming for ***

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acm sigplan NOTICES 2016年第10期51卷 531-547页

作者： Bonetta, Daniele Salucci, Luca Marr, Stefan Binder, Walter Oracle Labs Linz Austria Univ Svizzera Italiana Lugano Switzerland Johannes Kepler Univ Linz Linz Austria

JavaScript is the most popular programming language for client-side Web applications, and *** has popularized the language for server-side computing, too. In this domain, the minimal support for parallel programming remains however a major limitation. In this paper we introduce a novel parallel programming abstraction called Generic Messages (GEMS). GEMS allow one to combine message passing and shared-memory parallelism, extending the classes of parallel applications that can be built with ***. GEMS have customizable semantics and enable several forms of thread safety, isolation, and concurrency control. GEMS are designed as convenient JavaScript abstractions that expose high-level and safe parallelism models to the developer. Experiments show that GEMS outperform equivalent *** applications thanks to their usage of shared memory.

关键词： JavaScript Node.js Generic Messages

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Gentrification Gone too Far? Affordable 2nd-Class Values for Fun and (Co-)Effect

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acm sigplan NOTICES 2016年第10期51卷 234-251页

作者： Osvald, Leo Essertel, Gregory Wu, Xilun Gonzalez-Alayon, Lilliam I. Rompf, Tiark Purdue Univ W Lafayette IN 47907 USA

First-class functions dramatically increase expressiveness, at the expense of static guarantees. In ALGOL or PASCAL, functions could be passed as arguments but never escape their defining scope. Therefore, function arguments could serve as temporary access tokens or capabilities, enabling callees to perform some action, but only for the duration of the call. In modern languages, such programming patterns are no longer available. The central thrust of this paper is to re-introduce second-class functions and other values alongside first-class entities in modern languages. We formalize second-class values with stack-bounded lifetimes as an extension to simply-typed lambda calculus, and for richer type systems such as F-<: and systems with path-dependent types. We generalize the binary first-vs second-class distinction to arbitrary privilege lattices, with the underlying type lattice as a special case. In this setting, abstract types naturally enable privilege parametricity. We prove type soundness and lifetime properties in Coq. We implement our system as an extension of Scala, and present several case studies. First, we modify the Scala Collections library and add privilege annotations to all higher-order functions. Privilege parametricity is key to retain the high degree of code-reuse between sequential and parallel as well as lazy and eager collections. Second, we use scoped capabilities to introduce a model of checked exceptions in the Scala library, with only few changes to the code. Third, we employ second-class capabilities for memory safety in a region-based off-heap memory library.

关键词： first-class second-class types effects capabilities object lifetimes

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Ringer: Web Automation by Demonstration

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acm sigplan NOTICES 2016年第10期51卷 748-764页

作者： Barman, Shaon Chasins, Sarah Bodik, Rastislav Gulwani, Sumit Univ Calif Berkeley Berkeley CA 94720 USA Univ Washington Seattle WA 98195 USA Microsoft Res Cambridge MA USA

With increasing amounts of data available on the web and a diverse range of users interested in programmatically accessing that data, web automation must become easier. Automation helps users complete many tedious interactions, such as scraping data, completing forms, or transferring data between websites. However, writing web automation scripts typically requires an expert programmer because the writer must be able to reverse engineer the target webpage. We have built a record and replay tool, Ringer, that makes web automation accessible to non-coders. Ringer takes a user demonstration as input and creates a script that interacts with the page as a user would. This approach makes Ringer scripts more robust to webpage changes because user-facing interfaces remain relatively stable compared to the underlying webpage implementations. We evaluated our approach on benchmarks recorded on real webpages and found that it replayed 4x more benchmarks than a state-of-the-art replay tool.

关键词： Record-Replay Automation Javascript Browser Design languages

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Modeling and Analysis of Remote Memory Access programming

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acm sigplan NOTICES 2016年第10期51卷 129-144页

作者： Dan, Andrei Marian Lam, Patrick Hoefler, Torsten Vechev, Martin Swiss Fed Inst Technol Zurich Switzerland Univ Waterloo Waterloo ON N2L 3G1 Canada

Recent advances in networking hardware have led to a new generation of Remote Memory Access (RMA) networks in which processors from different machines can communicate directly, bypassing the operating system and allowing higher performance. Researchers and practitioners have proposed libraries and programming models for RMA to enable the development of applications running on these networks, However, the memory models implied by these RMA libraries and languages are often loosely specified, poorly understood, and differ depending on the underlying network architecture and other factors. Hence, it is difficult to precisely reason about the semantics of RMA programs or how changes in the network architecture affect them. We address this problem with the following contributions: (i) a coreRMA language which serves as a common foundation, formalizing the essential characteristics of RMA programming;(ii) complete axiomatic semantics for that language;(iii) integration of our semantics with an existing constraint solver, enabling us to exhaustively generate coreRMA programs (litmus tests) up to a specified bound and check whether the tests satisfy their specification;and (iv) extensive validation of our semantics on real-world RMA systems. We generated and ran 7,441 litmus tests using each of the low-level RMA network APIs: DMAPP, VPI Verbs, and Portals 4. Our results confirmed that our model successfully captures behaviors exhibited by these networks. Moreover, we found RMA programs that behave inconsistently with existing documentation, confirmed by network experts. Our work provides an important step towards understanding existing RMA networks, thus influencing the design of future RMA interfaces and hardware.

关键词： Memory Model

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IWST 2016 - Proceedings of the 11th international Workshop on Smalltalk Technologies, in conjunction with the 24th international Smalltalk Joint conference

IWST 2016 - Proceedings of the 11th International Workshop o...

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11th international Workshop on Smalltalk Technologies, IWST 2016

ISBN: (纸本)9781450345248

The proceedings contain 25 papers. The topics discussed include: CommunityExplorer: a framework for visualizing collaboration networks;SmalltalkCI: a continuous integration framework for smalltalk projects;ViennaTalk and Assertch: building lightweight formal methods environments on Pharo;when quality-assistant meets Pharo: enforced code critiques motivate more valuable rules;inferring types by mining class usage frequency from inline caches;the object repository - pulling objects out of the ecosystem;dynamically composing collection operations through collection promises;Pragmas: literal messages as powerful method annotations;mocks, proxies, and transpilation as development strategies for web development;clustering technique for conceptual clusters;prototyping software product lines analysis with Pharo;Lub: a DSL for dynamic context oriented programming;the OpenPonk modeling platform;dynamic round-trip engineering in the context of FOMDD;Phorms: pattern combinator library for Pharo;test selection with Moose In industry - impact of granularity;a promising approach for debugging remote promises;and chromatic and harmonic scales for intuitive sonographic compositions.

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