Scott West

ETH Zurich, Zürich, Zurich, Switzerland

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Publications (6)0 Total impact

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    ABSTRACT: Making threaded programs safe and easy to reason about is one of the chief difficulties in modern programming. This work provides an efficient execution model for SCOOP, a concurrency approach that provides not only data race freedom but also pre/postcondition reasoning guarantees between threads. The extensions we propose influence both the underlying semantics to increase the amount of concurrent execution that is possible, exclude certain classes of deadlocks, and enable greater performance. These extensions are used as the basis an efficient runtime and optimization pass that improve performance 15x over a baseline implementation. This new implementation of SCOOP is also 2x faster than other well-known safe concurrent languages. The measurements are based on both coordination-intensive and data-manipulation-intensive benchmarks designed to offer a mixture of workloads.
    05/2014;
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    ABSTRACT: Developers face a wide choice of programming languages and libraries supporting multicore computing. Ever more diverse paradigms for expressing parallelism and synchronization become available while their influence on usability and performance remains largely unclear. This paper describes an experiment comparing four markedly different approaches to parallel programming: Chapel, Cilk, Go, and Threading Building Blocks (TBB). Each language is used to implement sequential and parallel versions of six benchmark programs. The implementations are then reviewed by notable experts in the language, thereby obtaining reference versions for each language and benchmark. The resulting pool of 96 implementations is used to compare the languages with respect to source code size, coding time, execution time, and speedup. The experiment uncovers strengths and weaknesses in all approaches, facilitating an informed selection of a language under a particular set of requirements. The expert review step furthermore highlights the importance of expert knowledge when using modern parallel programming approaches.
    02/2013;
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    ABSTRACT: The development of concurrent applications is challenging because of the complexity of concurrent designs and the hazards of concurrent programming. Architectural modeling using the Unified Modeling Language (UML) can support the development process, but the problem of mapping the model to a concurrent implementation remains. This paper addresses this problem by defining a scheme to map concurrent UML designs to a concurrent object-oriented program. Using the COMET method for the architectural design of concurrent object-oriented systems, each component and connector is annotated with a stereotype indicating its behavioral design pattern. For each of these patterns, a reference implementation is provided using SCOOP, a concurrent object-oriented programming model. We evaluate this development process using a case study of an ATM system, obtaining a fully functional implementation based on the systematic mapping of the individual patterns. Given the strong execution guarantees of the SCOOP model, which is free of data races by construction, this development method eliminates a source of intricate concurrent programming errors.
    12/2012;
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    ABSTRACT: Testing presents a daunting challenge for concurrent programs, as non-deterministic scheduling defeats reproducibility. The problem is even harder if, rather than testing entire systems, one tries to test individual components, for example to assess them for thread-safety. We present demonic testing, a technique combining the tangible results of unit testing with the rigour of formal rely-guarantee reasoning to provide deterministic unit testing for concurrent programs. Deterministic execution is provided by abstracting threads away via rely-guarantee reasoning, and replacing them with "demonic" sequences of interfering instructions that drive the program to break invariants. Demonic testing reuses existing unit tests to drive the routine under test, using the execution to discover demonic interference. Programs carry contract-based rely-guarantee style specifications to express what sort of thread interference should be tolerated. Aiding the demonic testing technique is an interference synthesis tool we have implemented based on SMT solving. The technique is shown to find errors in contracted versions of several benchmark applications.
    14th International Conference on Formal Engineering Methods (ICFEM'12); 01/2012
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    ABSTRACT: Despite the advancements of concurrency theory in the past decades, practical concurrent programming has remained a challenging activity. Fundamental problems such as data races and deadlocks still persist for programmers since available detection and prevention tools are unsound or have otherwise not been well adopted. In an alternative approach, programming models that exclude certain classes of errors by design can address concurrency problems at a language level. In this paper we review SCOOP, an existing race-free programming model for concurrent object-oriented programming, and extend it with a scheme for deadlock prevention based on locking orders. The scheme facilitates modular reasoning about deadlocks by associating annotations with the interfaces of routines. We prove deadlock-freedom of well-formed programs using a rigorous formalization of the locking semantics of the programming model. The scheme has been implemented and we demonstrate its usefulness by applying it to the example of a simple web server.
    Formal Methods and Software Engineering - 12th International Conference on Formal Engineering Methods, ICFEM 2010, Shanghai, China, November 17-19, 2010. Proceedings; 01/2010
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    Scott West, Wolfram Kahl
    ECEASST. 01/2009; 18.