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acm sigplan conference on programming language design and implementation

作者： Rishabh Singh Sumit Gulwani Armando Solar-Lezama MIT CSAIL Microsoft Research

ISBN: (纸本)9781450320146

We present a new method for automatically providing feedback for introductory programming problems. In order to use this method, we need a reference implementation of the assignment, and an error model consisting of potential corrections to errors that students might make. Using this information, the system automatically derives minimal corrections to student's incorrect solutions, providing them with a measure of exactly how incorrect a given solution was, as well as feedback about what they did wrong. We introduce a simple language for describing error models in terms of correction rules, and formally define a rule-directed translation strategy that reduces the problem of finding minimal corrections in an incorrect program to the problem of synthesizing a correct program from a sketch. We have evaluated our system on thousands of real student attempts obtained from the Introduction to programming course at MIT (6.00) and MITx (6.00x). Our results show that relatively simple error models can correct on average 64% of all incorrect submissions in our benchmark set.

关键词： Automated Grading Computer-Aided Education Program Synthesis error model computer-assisted education Feedback programming Students AUTOMATIC

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CONCURRIT: A Domain Specific language for Reproducing Concurrency Bugs 13

CONCURRIT: A Domain Specific Language for Reproducing Concur...

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acm sigplan conference on programming language design and implementation

作者： Tayfun Elmas Jacob Burnim George Necula Koushik Sen Google Inc. Sift Science Inc. Department of Electrical Engineering and Computer Sciences University of California

ISBN: (纸本)9781450320146

We present CONCURRIT, a domain-specific language (DSL) for reproducing concurrency bugs. Given some partial information about the nature of a bug in an application, a programmer can write a CONCURRIT script to formally and concisely specify a set of thread schedules to explore in order to find a schedule exhibiting the bug. Further, the programmer can specify how these thread schedules should be searched to find a schedule that reproduces the bug. We implemented CONCURRIT as an embedded DSL in C++, which uses manual or automatic source instrumentation to partially control the scheduling of the software under test. Using CONCURRIT, we were able to write concise tests to reproduce concurrency bugs in a variety of benchmarks, including the Mozilla's SpiderMon-key JavaScript engine, Memcached, Apache's HTTP server, and MySQL.

关键词： Concurrency Errors Domain-Specific languages Software Testing

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Hybrid Context-Sensitivity for Points-To Analysis 13

Hybrid Context-Sensitivity for Points-To Analysis

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acm sigplan conference on programming language design and implementation

作者： George Kastrinis Yannis Smaragdakis Department of Informatics University of Athens

ISBN: (纸本)9781450320146

Context-sensitive points-to analysis is valuable for achieving high precision with good performance. The standard flavors of context-sensitivity are call-site-sensitivity (kCFA) and object-sensitivity. Combining both flavors of context-sensitivity increases precision but at an infeasibly high cost. We show that a selective combination of call-site- and object-sensitivity for Java points-to analysis is highly profitable. Namely, by keeping a combined context only when analyzing selected language features, we can closely approximate the precision of an analysis that keeps both contexts at all times. In terms of speed, the selective combination of both kinds of context not only vastly outperforms non-selective combinations but is also faster than a mere object-sensitive analysis. This result holds for a large array of analyses (e.g., 1-object-sensitive, 2-object-sensitive with a context-sensitive heap, type-sensitive) establishing a new set of performance/precision sweet spots.

关键词： Points-to analysis Context-sensitivity Object-sensitivity Type-sensitivity Algorithms languages Performance language algorithms Analysis Flavoring Agents Precision language feature

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Fast Algorithms for Dyck-CFL-Reachability with Applications to Alias Analysis 13

Fast Algorithms for Dyck-CFL-Reachability with Applications ...

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acm sigplan conference on programming language design and implementation

作者： Qirun Zhang Michael R. Lyu Hao Yuan Zhendong Su The Chinese University of Hong Kong BOPU Technologies University of California

ISBN: (纸本)9781450320146

The context-free language (CFL) reachability problem is a well-known fundamental formulation in program analysis. In practice, many program analyses, especially pointer analyses, adopt a restricted version of CFL-reachability, Dyck-CFL-reachability, and compute on edge-labeled bidirected graphs. Solving the all-pairs Dyck-CFL-reachability on such bidirected graphs is expensive. For a bidirected graph with n nodes and m edges, the traditional dynamic programming style algorithm exhibits a subcubic time complexity for the Dyck language with k kinds of parentheses. When the underlying graphs are restricted to bidirected trees, an algorithm with O(n log n log k) time complexity was proposed recently. This paper studies the Dyck-CFL-reachability problems on bidirected trees and graphs. In particular, it presents two fast algorithms with O(n) and O(n + m log m) time complexities on trees and graphs respectively. We have implemented and evaluated our algorithms on a state-of-the-art alias analysis for Java. Results on standard benchmarks show that our algorithms achieve orders of magnitude speedup and consume less memory.

关键词： Dyck-CFL-reachability Alias analysis Algorithms design Experimentation languages algorithms language experimentation analysis programme complexity classes Parentheses logs logarithm (log)

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A General Constraint-centric Scheduling Framework for Spatial Architectures 13

A General Constraint-centric Scheduling Framework for Spatia...

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acm sigplan conference on programming language design and implementation

作者： Tony Nowatzki Michael Sartin-Tarm Lorenzo De Carli Karthikeyan Sankaralingam Cristian Estan Behnam Robatmili University of Wisconsin-Madison Broadcom Qualcomm Research Silicon Valley

ISBN: (纸本)9781450320146

Specialized execution using spatial architectures provides energy efficient computation, but requires effective algorithms for spatially scheduling the computation. Generally, this has been solved with architecture-specific heuristics, an approach which suffers from poor compiler/architect productivity, lack of insight on optimality, and inhibits migration of techniques between architectures. Our goal is to develop a scheduling framework usable for all spatial architectures. To this end, we expresses spatial scheduling as a constraint satisfaction problem using Integer Linear programming (ILP). We observe that architecture primitives and scheduler responsibilities can be related through five abstractions: placement of computation, routing of data, managing event timing, managing resource utilization, and forming the optimization objectives. We encode these responsibilities as 20 general ILP constraints, which are used to create schedulers for the disparate TRIPS, DySER, and PLUG architectures. Our results show that a general declarative approach using ILP is implementable, practical, and typically matches or outperforms specialized schedulers.

关键词： Spatial Architectures Spatial Architecture Scheduling Integer Linear programming

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Static Analysis for Probabilistic Programs: Inferring Whole Program Properties from Finitely Many Paths 13

Static Analysis for Probabilistic Programs: Inferring Whole ...

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acm sigplan conference on programming language design and implementation

作者： Sriram Sankaranarayanan Aleksandar Chakarov Sumit Gulwani University of Colorado Microsoft Research

ISBN: (纸本)9781450320146

We propose an approach for the static analysis of probabilistic programs that sense, manipulate, and control based on uncertain data. Examples include programs used in risk analysis, medical decision making and cyber-physical systems. Correctness properties of such programs take the form of queries that seek the probabilities of assertions over program variables. We present a static analysis approach that provides guaranteed interval bounds on the values (assertion probabilities) of such queries. First, we observe that for probabilistic programs, it is possible to conclude facts about the behavior of the entire program by choosing a finite, adequate set of its paths. We provide strategies for choosing such a set of paths and verifying its adequacy. The queries are evaluated over each path by a combination of symbolic execution and probabilistic volume-bound computations. Each path yields interval bounds that can be summed up with a "coverage" bound to yield an interval that encloses the probability of assertion for the program as a whole. We demonstrate promising results on a suite of benchmarks from many different sources including robotic manipulators and medical decision making programs.

关键词： Probabilistic programming Program Verification Volume Bounding Symbolic Execution Monte-Carlo Sampling

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P: Safe Asynchronous Event-Driven programming 13

P: Safe Asynchronous Event-Driven Programming

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acm sigplan conference on programming language design and implementation

作者： Ankush Desai Vivek Gupta Ethan Jackson Shaz Qadeer Sriram Rajamani Damien Zufferey Microsoft IST Austria

ISBN: (纸本)9781450320146

We describe the design and implementation of P, a domain-specific language to write asynchronous event driven code. P allows the programmer to specify the system as a collection of interacting state machines, which communicate with each other using events. P unifies modeling and programming into one activity for the programmer. Not only can a P program be compiled into executable code, but it can also be tested using model checking techniques. P allows the programmer to specify the environment, used to "close" the system during testing, as nondeterministic ghost machines. Ghost machines are erased during compilation to executable code; a type system ensures that the erasure is semantics preserving. The P language is designed so that a P program can be checked for responsiveness-the ability to handle every event in a timely manner. By default, a machine needs to handle every event that arrives in every state. But handling every event in every state is impractical. The language provides a notion of deferred events where the programmer can annotate when she wants to delay processing an event. The default safety checker looks for presence of unhandled events. The language also provides default liveness checks that an event cannot be potentially deferred forever. P was used to implement and verify the core of the USB device driver stack that ships with Microsoft Windows 8. The resulting driver is more reliable and performs better than its prior incarnation (which did not use P); we have more confidence in the robustness of its design due to the language abstractions and verification provided by P.

关键词： Domain-specific language Device driver Event-driven programming State machine Verification Systematic testing state machines Computer personnel event-driven programming Verification device drivers Phosphorus Executable code Device Programmer Component application-specific language language Microsoft Windows(software)

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TRANSIT: Specifying Protocols with Concolic Snippets 13

TRANSIT: Specifying Protocols with Concolic Snippets

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acm sigplan conference on programming language design and implementation

作者： Abhishek Udupa Sela Mador-Haim Arun Raghavan Milo M. K. Martin Jyotirmoy V. Deshmukh Rajeev Alur University of Pennsylvania Toyota Technical Center

ISBN: (纸本)9781450320146

With the maturing of technology for model checking and constraint solving, there is an emerging opportunity to develop programming tools that can transform the way systems are specified. In this paper, we propose a new way to program distributed protocols using concolic snippets. Concolic snippets are sample execution fragments that contain both concrete and symbolic values. The proposed approach allows the programmer to describe the desired system partially using the traditional model of communicating extended finite-state-machines (EFSM), along with high-level invariants and concrete execution fragments. Our synthesis engine completes an EFSM skeleton by inferring guards and updates from the given fragments which is then automatically analyzed using a model checker with respect to the desired invariants. The counterexamples produced by the model checker can then be used by the programmer to add new concrete execution fragments that describe the correct behavior in the specific scenario corresponding to the counterexample. We describe TRANSIT, a language and prototype implementation of the proposed specification methodology for distributed protocols. Experimental evaluations of TRANSIT to specify cache coherence protocols show that (1) the algorithm for expression inference from concolic snippets can synthesize expressions of size 15 involving typical operators over commonly occurring types, (2) for a classical directory-based protocol, TRANSIT automatically generates, in a few seconds, a complete implementation from a specification consisting of the EFSM structure and a few concrete examples for every transition, and (3) a published partial description of the SGI Origin cache coherence protocol maps directly to symbolic examples and leads to a complete implementation in a few iterations, with the programmer correcting counterexamples resulting from underspecified transitions by adding concrete examples in each iteration.

关键词： Program Synthesis Distributed Protocol Synthesis Cache Coherence Protocols programming by Example

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Isolation for Nested Task Parallelism

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acm sigplan NOTICES 2013年第10期48卷 571-587页

作者： Zhao, Jisheng Lublinerman, Roberto Budimlic, Zoran Chaudhuri, Swarat Sarkar, Vivek Rice Univ Houston TX 77251 USA Google Inc Mountain View CA USA

Isolation-the property that a task can access shared data without interference from other tasks-is one of the most basic concerns in parallel programming. While there is a large body of past work on isolated task-parallelism, the integration of isolation, task-parallelism, and nesting of tasks has been a difficult and unresolved challenge. In this paper, we present a programming and execution model called Otello where isolation is extended to arbitrarily nested parallel tasks with irregular accesses to heap data. At the same time, no additional burden is imposed on the programmer, who only exposes parallelism by creating and synchronizing parallel tasks, leaving the job of ensuring isolation to the underlying compiler and runtime system. Otello extends our past work on Aida execution model and the delegated isolation mechanism [22] to the setting of nested parallelism. The basic runtime construct in Aida and Otello is an assembly: a task equipped with a region in the shared heap that it owns. When an assembly A conflicts with an assembly B, A transfers-or delegates-its code and owned region to a carefully selected assembly C in a way that will ensure isolation with B, leaving the responsibility of re-executing task A to C. The choice of C depends on the nesting relationship between A and B. We have implemented Otello on top of the Habanero Java (HJ) parallel programming language [8], and used this implementation to evaluate Otello on collections of nested task-parallel benchmarks and non-nested transactional benchmarks from past work. On the nested task-parallel bench-marks, Otello achieves scalability comparable to HJ programs without built-in isolation, and the relative overhead of Otello is lower than that of many published data-race detection algorithms that detect the isolation violations (but do not enforce isolation). For the transactional benchmarks, Otello incurs lower overhead than a state-of-the-art software transactional memory system (Deuce STM).

关键词： languages design Isolation programming abstractions Irregular parallelism Contention

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General Data Structure Expansion for Multi-threading 13

General Data Structure Expansion for Multi-threading

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acm sigplan conference on programming language design and implementation

作者： Hongtao Yu Hou-Jen Ko Zhiyuan Li Department of Computer Science Purdue University

ISBN: (纸本)9781450320146

Among techniques for parallelizing sequential codes, privatization is a common and significant transformation performed by both compilers and runtime parallelizing systems. Without privatization, repetitive updates to the same data structures often introduce spurious data dependencies that hide the inherent parallelism. Unfortunately, it remains a significant challenge to compilers to automatically privatize dynamic and recursive data structures which appear frequently in real applications written in languages such as C/C++. This is because such languages lack a naming mechanism to define the address range of a pointer-based data structure, in contrast to arrays with explicitly declared bounds. In this paper we present a novel solution to this difficult problem by expanding general data structures such that memory accesses issued from different threads to contentious data structures are directed to different data fields. Based on compile-time type checking and a data dependence graph, this aggressive extension to the traditional scalar and array expansion isolates the address ranges among different threads, without struggling with privatization based on thread-private stacks, such that the targeted loop can be effectively parallelized. With this method fully implemented in GCC, experiments are conducted on a set of programs from well-known benchmark suites such as Mibench, MediaBench II and SPECint. Results show that the new approach can lead to a high speedup when executing the transformed code on multiple cores.

关键词： Parallelization Privatization Multithreading Algorithms languages Performance Privatisation Multithreading Data structures language parallelization data dependency compilers algorithms type checking

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