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acm sigplan NOTICES 2016年第6期51卷 369-385页

作者： McClurg, Jedidiah Hojjat, Hossein Foster, Nate Cerny, Pavol CU Boulder Boulder CO 80309 USA Cornell Univ Ithaca NY 14853 USA

Software-defined networking (SDN) programs must simultaneously describe static forwarding behavior and dynamic updates in response to events. Event-driven updates are critical to get right, but difficult to implement correctly due to the high degree of concurrency in networks. Existing SDN platforms offer weak guarantees that can break application invariants, leading to problems such as dropped packets, degraded performance, security violations, etc. This paper introduces event-driven consistent updates that are guaranteed to preserve well-defined behaviors when transitioning between configurations in response to events. We propose network event structures (NESs) to model constraints on updates, such as which events can be enabled simultaneously and causal dependencies between events. We define an extension of the NetKAT language with mutable state, give semantics to stateful programs using NESs, and discuss provably-correct strategies for implementing NESs in SDNs. Finally, we evaluate our approach empirically, demonstrating that it gives well-defined consistency guarantees while avoiding expensive synchronization and packet buffering.

关键词： network update consistent update event structure software-defined networking SDN NetKAT

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Higher-Order and Tuple-Based Massively-Parallel Prefix Sums

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acm sigplan NOTICES 2016年第6期51卷 539-552页

作者： Maleki, Sepideh Yang, Annie Burtscher, Martin Texas State Univ Dept Comp Sci San Marcos TX 78666 USA

Prefix sums are an important parallel primitive, especially in massively-parallel programs. This paper discusses two orthogonal generalizations thereof, which we call higher-order and tuple-based prefix sums. Moreover, it describes and evaluates SAM, a GPU-friendly algorithm for computing prefix sums and other scans that directly supports higher orders and tuple values. Its templated CUDA implementation unifies all of these computations in a single 100-statement kernel. SAM is communication-efficient in the sense that it minimizes main-memory accesses. When computing prefix sums of a million or more values, it outperforms Thrust and CUDPP on both a Titan X and a K40 GPU. On the Titan X, SAM reaches memory-copy speeds for large input sizes, which cannot be surpassed. SAM outperforms CUB, the currently fastest conventional prefix sum implementation, by up to a factor of 2.9 on eighth-order prefix sums and by up to a factor of 2.6 on eight-tuple prefix sums.

关键词： Algorithms Performance design Higher-order prefix sums tuple-based prefix sums carry propagation GPU programming

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Program Synthesis from Polymorphic Refinement Types

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acm sigplan NOTICES 2016年第6期51卷 522-538页

作者： Polikarpova, Nadia Kuraj, Ivan Solar-Lezama, Armando MIT CSAIL Cambridge MA USA

We present a method for synthesizing recursive functions that provably satisfy a given specification in the form of a polymorphic refinement type. We observe that such specifications are particularly suitable for program synthesis for two reasons. First, they offer a unique combination of expressive power and decidability, which enables automatic verification-and hence synthesis-of nontrivial programs. Second, a type-based specification for a program can often be effectively decomposed into independent specifications for its components, causing the synthesizer to consider fewer component combinations and leading to a combinatorial reduction in the size of the search space. At the core of our synthesis procedure is a newalgorithm for refinement type checking, which supports specification decomposition. We have evaluated our prototype implementation on a large set of synthesis problems and found that it exceeds the state of the art in terms of both scalability and usability. The tool was able to synthesize more complex programs than those reported in prior work (several sorting algorithms and operations on balanced search trees), as well as most of the benchmarks tackled by existing synthesizers, often starting from a more concise and intuitive user input.

关键词： languages Verification Program Synthesis Functional programming Refinement Types Predicate Abstraction

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GreenWeb: language Extensions for Energy-Efficient Mobile Web Computing

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acm sigplan NOTICES 2016年第6期51卷 145-160页

作者： Zhu, Yuhao Reddi, Vijay Janapa Univ Texas Austin Dept Elect & Comp Engn Austin TX 78712 USA

Web computing is gradually shifting toward mobile devices, in which the energy budget is severely constrained. As a result, Web developers must be conscious of energy efficiency. However, current Web languages provide developers little control over energy consumption. In this paper, we take a first step toward language-level research to enable energy-efficient Web computing. Our key motivation is that mobile systems can wisely budget energy usage if informed with user quality-of-service (QoS) constraints. To do this, programmers need new abstractions. We propose two language abstractions, QoS type and QoS target, to capture two fundamental aspects of user QoS experience. We then present Green Web, a set of language extensions that empower developers to easily express the QoS abstractions as program annotations. As a proof of concept, we develop a GreenWeb runtime, which intelligently determines how to deliver specified user QoS expectation while minimizing energy consumption. Overall, GreenWeb shows significant energy savings (29.2% similar to 66.0%) over Android's default Interactive governor with few QoS violations. Our work demonstrates a promising first step toward language innovations for energy-efficient Web computing.

关键词： Energy-efficiency Web Mobile computing

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A Distributed OpenCL Framework using Redundant Computation and Data Replication

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acm sigplan NOTICES 2016年第6期51卷 553-569页

作者： Kim, Junghyun Jo, Gangwon Jung, Jaehoon Kim, Jungwon Lee, Jaejin Seoul Natl Univ Ctr Manycore Programming Dept Comp Sci & Engn Seoul 08826 South Korea

Applications written solely in OpenCL or CUDA cannot execute on a cluster as a whole. Most previous approaches that extend these programming models to clusters are based on a common idea: designating a centralized host node and coordinating the other nodes with the host for computation. However, the centralized host node is a serious performance bottleneck when the number of nodes is large. In this paper, we propose a scalable and distributed OpenCL framework called SnuCL-D for large-scale clusters. SnuCL-D's remote device virtualization provides an OpenCL application with an illusion that all compute devices in a cluster are confined in a single node. To reduce the amount of control-message and data communication between nodes, SnuCL-D replicates the OpenCL host program execution and data in each node. We also propose a new OpenCL host API function and a queueing optimization technique that significantly reduce the overhead incurred by the previous centralized approaches. To show the effectiveness of SnuCL-D, we evaluate SnuCL-D with a microbenchmark and eleven benchmark applications on a large-scale CPU cluster and a medium-scale GPU cluster.

关键词： OpenCL clusters heterogeneous computing programming models runtime systems redundant computation data replication

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Disjoint Intersection Types

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acm sigplan NOTICES 2016年第9期51卷 364-377页

作者： Oliveira, Bruno C. d. S. Shi, Zhiyuan Alpuim, Joao Univ Hong Kong Hong Kong Hong Kong Peoples R China

Dunfield showed that a simply typed core calculus with intersection types and a merge operator is able to capture various programming language features. While his calculus is type-safe, it is not coherent: different derivations for the same expression can elaborate to expressions that evaluate to different values. The lack of coherence is an important disadvantage for adoption of his core calculus in implementations of programming languages, as the semantics of the programming language becomes implementation-dependent. This paper presents lambda(i) : a coherent and type-safe calculus with a form of intersection types and a merge operator. Coherence is achieved by ensuring that intersection types are disjoint and programs are sufficiently annotated to avoid type ambiguity. We propose a definition of disjointness where two types A and B are disjoint only if certain set of types are common supertypes of A and B. We investigate three different variants of lambda(i), with three variants of disjointness. In the simplest variant, which does not allow inverted perpendicular types, two types are disjoint if they do not share any common supertypes at all. The other two variants introduce inverted perpendicular types and refine the notion of disjointness to allow two types to be disjoint when the only the set of common supertypes are top-like. The difference between the two variants with inverted perpendicular types is on the definition of top-like types, which has an impact on which types are allowed on intersections. We present a type system that prevents intersection types that are not disjoint, as well as an algorithmic specifications to determine whether two types are disjoint for all three variants.

关键词： Intersection Types Type System design languages Theory

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Occurrence Typing Modulo Theories

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acm sigplan NOTICES 2016年第6期51卷 296-309页

作者： Kent, Andrew M. Kempe, David Tobin-Hochstadt, Sam Indiana Univ Bloomington IN 47405 USA

We present a new type system combining occurrence typing- a technique previously used to type check programs in dynamically-typed languages such as Racket, Clojure, and JavaScript-with dependent refinement types. We demonstrate that the addition of refinement types allows the integration of arbitrary solver-backed reasoning about logical propositions from external theories. By building on occurrence typing, we can add our enriched type system as a natural extension of Typed Racket, reusing its core while increasing its expressiveness. The result is a well-tested type system with a conservative, decidable core in which types may depend on a small but extensible set of program terms. In addition to describing our design, we present the following: a formal model and proof of correctness;a strategy for integrating new theories, with specific examples including linear arithmetic and bitvectors;and an evaluation in the context of the full Typed Racket implementation. Specifically, we take safe vector operations as a case study, examining all vector accesses in a 56,000 line corpus of Typed Racket programs. Our system is able to prove that 50% of these are safe with no new annotations, and with a few annotations and modifications we capture more than 70%.

关键词： languages design Verification Refinement types occurrence typing Racket

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Latte: A language, Compiler, and Runtime for Elegant and Efficient Deep Neural Networks

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acm sigplan NOTICES 2016年第6期51卷 209-223页

作者： Truong, Leonard Barik, Rajkishore Totoni, Ehsan Liu, Hai Markley, Chick Fox, Armando Shpeisman, Tatiana Univ Calif Berkeley Intel Labs Berkeley CA USA Intel Labs Berkeley CA USA Univ Calif Berkeley Berkeley CA USA

Deep neural networks (DNNs) have undergone a surge in popularity with consistent advances in the state of the art for tasks including image recognition, natural language processing, and speech recognition. The computationally expensive nature of these networks has led to the proliferation of implementations that sacrifice abstraction for high performance. In this paper, we present Latte, a domain-specific language for DNNs that provides a natural abstraction for specifying new layers without sacrificing performance. Users of Latte express DNNs as ensembles of neurons with connections between them. The Latte compiler synthesizes a program based on the user specification, applies a suite of domain-specific and general optimizations, and emits efficient machine code for heterogeneous architectures. Latte also includes a communication runtime for distributed memory data-parallelism. Using networks described using Latte, we demonstrate 3-6x speedup over Caffe (C++/MKL) on the three state-of-the-art ImageNet models executing on an Intel Xeon E5-2699 v3 x86 CPU.

关键词： Deep Learning Neural Networks Domain Specific language Compiler Optimization

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A design and Verification Methodology for Secure Isolated Regions

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acm sigplan NOTICES 2016年第6期51卷 665-681页

作者： Sinha, Rohit Costa, Manuel Lal, Akash Lopes, Nuno P. Rajamani, Sriram Seshia, Sanjit A. Vaswani, Kapil Univ Calif Berkeley Berkeley CA 94720 USA Microsoft Res London England Microsoft Res Bengaluru Karnataka India

Hardware support for isolated execution (such as Intel SGX) enables development of applications that keep their code and data confidential even while running on a hostile or compromised host. However, automatically verifying that such applications satisfy confidentiality remains challenging. We present a methodology for designing such applications in a way that enables certifying their confidentiality. Our methodology consists of forcing the application to communicate with the external world through a narrow interface, compiling it with runtime checks that aid verification, and linking it with a small runtime library that implements the interface. The runtime library includes core services such as secure communication channels and memory management. We formalize this restriction on the application as Information Release Confinement (IRC), and we show that it allows us to decompose the task of proving confidentiality into (a) one-time, human-assisted functional verification of the runtime to ensure that it does not leak secrets, (b) automatic verification of the application's machine code to ensure that it satisfies IRC and does not directly read or corrupt the runtime's internal state. We present/CONFIDENTIAL: a verifier for IRC that is modular, automatic, and keeps our compiler out of the trusted computing base. Our evaluation suggests that the methodology scales to real-world applications.

关键词： Enclave Programs Secure Computation Confidentiality Formal Verification

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End-to-End Verification of Information-Flow Security for C and Assembly Programs

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acm sigplan NOTICES 2016年第6期51卷 648-664页

作者： Costanzo, David Shao, Zhong Gu, Ronghui Yale Univ New Haven CT 06520 USA

Protecting the confidentiality of information manipulated by a computing system is one of the most important challenges facing today's cybersecurity community. A promising step toward conquering this challenge is to formally verify that the end-to-end behavior of the computing system really satisfies various information-flow policies. Unfortunately, because today's system software still consists of both C and assembly programs, the end-to-end verification necessarily requires that we not only prove the security properties of individual components, but also carefully preserve these properties through compilation and cross-language linking. In this paper, we present a novel methodology for formally verifying end-to-end security of a software system that consists of both C and assembly programs. We introduce a general definition of observation function that unifies the concepts of policy specification, state indistinguishability, and whole-execution behaviors. We show how to use different observation functions for different levels of abstraction, and how to link different security proofs across abstraction levels using a special kind of simulation that is guaranteed to preserve state indistinguishability. To demonstrate the effectiveness of our new methodology, we have successfully constructed an end-to-end security proof, fully formalized in the Coq proof assistant, of a nontrivial operating system kernel (running on an extended CompCert x86 assembly machine model). Some parts of the kernel are written in C and some are written in assembly;we verify all of the code, regardless of language.

关键词： Verification Security Reliability languages design Information Flow Control Security Policy Specification Security-Preserving Simulation Program Verification Certified OS Kernels

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