61,392 research outputs found
A Graph-Based Semantics Workbench for Concurrent Asynchronous Programs
A number of novel programming languages and libraries have been proposed that
offer simpler-to-use models of concurrency than threads. It is challenging,
however, to devise execution models that successfully realise their
abstractions without forfeiting performance or introducing unintended
behaviours. This is exemplified by SCOOP---a concurrent object-oriented
message-passing language---which has seen multiple semantics proposed and
implemented over its evolution. We propose a "semantics workbench" with fully
and semi-automatic tools for SCOOP, that can be used to analyse and compare
programs with respect to different execution models. We demonstrate its use in
checking the consistency of semantics by applying it to a set of representative
programs, and highlighting a deadlock-related discrepancy between the principal
execution models of the language. Our workbench is based on a modular and
parameterisable graph transformation semantics implemented in the GROOVE tool.
We discuss how graph transformations are leveraged to atomically model
intricate language abstractions, and how the visual yet algebraic nature of the
model can be used to ascertain soundness.Comment: Accepted for publication in the proceedings of FASE 2016 (to appear
Equivariance In Higher Geometry
We study (pre-)sheaves in bicategories on geometric categories: smooth
manifolds, manifolds with a Lie group action and Lie groupoids. We present
three main results: we describe equivariant descent, we generalize the plus
construction to our setting and show that the plus construction yields a
2-stackification for 2-prestacks. Finally we show that, for a 2-stack, the
pullback functor along a Morita-equivalence of Lie groupoids is an equivalence
of bicategories. Our results have direct applications to gerbes and 2-vector
bundles. For instance, they allow to construct equivariant gerbes from local
data and can be used to simplify the description of the local data. We
illustrate the usefulness of our results in a systematic discussion of
holonomies for unoriented surfaces.Comment: 42 pages, minor correction
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