293 research outputs found
Taming Numbers and Durations in the Model Checking Integrated Planning System
The Model Checking Integrated Planning System (MIPS) is a temporal least
commitment heuristic search planner based on a flexible object-oriented
workbench architecture. Its design clearly separates explicit and symbolic
directed exploration algorithms from the set of on-line and off-line computed
estimates and associated data structures. MIPS has shown distinguished
performance in the last two international planning competitions. In the last
event the description language was extended from pure propositional planning to
include numerical state variables, action durations, and plan quality objective
functions. Plans were no longer sequences of actions but time-stamped
schedules. As a participant of the fully automated track of the competition,
MIPS has proven to be a general system; in each track and every benchmark
domain it efficiently computed plans of remarkable quality. This article
introduces and analyzes the most important algorithmic novelties that were
necessary to tackle the new layers of expressiveness in the benchmark problems
and to achieve a high level of performance. The extensions include critical
path analysis of sequentially generated plans to generate corresponding optimal
parallel plans. The linear time algorithm to compute the parallel plan bypasses
known NP hardness results for partial ordering by scheduling plans with respect
to the set of actions and the imposed precedence relations. The efficiency of
this algorithm also allows us to improve the exploration guidance: for each
encountered planning state the corresponding approximate sequential plan is
scheduled. One major strength of MIPS is its static analysis phase that grounds
and simplifies parameterized predicates, functions and operators, that infers
knowledge to minimize the state description length, and that detects domain
object symmetries. The latter aspect is analyzed in detail. MIPS has been
developed to serve as a complete and optimal state space planner, with
admissible estimates, exploration engines and branching cuts. In the
competition version, however, certain performance compromises had to be made,
including floating point arithmetic, weighted heuristic search exploration
according to an inadmissible estimate and parameterized optimization
Large-Scale Analysis of Framework-Specific Exceptions in Android Apps
Mobile apps have become ubiquitous. For app developers, it is a key priority
to ensure their apps' correctness and reliability. However, many apps still
suffer from occasional to frequent crashes, weakening their competitive edge.
Large-scale, deep analyses of the characteristics of real-world app crashes can
provide useful insights to guide developers, or help improve testing and
analysis tools. However, such studies do not exist -- this paper fills this
gap. Over a four-month long effort, we have collected 16,245 unique exception
traces from 2,486 open-source Android apps, and observed that
framework-specific exceptions account for the majority of these crashes. We
then extensively investigated the 8,243 framework-specific exceptions (which
took six person-months): (1) identifying their characteristics (e.g.,
manifestation locations, common fault categories), (2) evaluating their
manifestation via state-of-the-art bug detection techniques, and (3) reviewing
their fixes. Besides the insights they provide, these findings motivate and
enable follow-up research on mobile apps, such as bug detection, fault
localization and patch generation. In addition, to demonstrate the utility of
our findings, we have optimized Stoat, a dynamic testing tool, and implemented
ExLocator, an exception localization tool, for Android apps. Stoat is able to
quickly uncover three previously-unknown, confirmed/fixed crashes in Gmail and
Google+; ExLocator is capable of precisely locating the root causes of
identified exceptions in real-world apps. Our substantial dataset is made
publicly available to share with and benefit the community.Comment: ICSE'18: the 40th International Conference on Software Engineerin
Using heuristic search for finding deadlocks in concurrent systems
AbstractModel checking is a formal technique for proving the correctness of a system with respect to a desired behavior. This is accomplished by checking whether a structure representing the system (typically a labeled transition system) satisfies a temporal logic formula describing the expected behavior. Model checking has a number of advantages over traditional approaches that are based on simulation and testing: it is completely automatic and when the verification fails it returns a counterexample that can be used to pinpoint the source of the error. Nevertheless, model checking techniques often fail because of the state explosion problem: transition systems grow exponentially with the number of components. The aim of this paper is to attack the state explosion problem that may arise when looking for deadlocks in concurrent systems described through the calculus of communicating systems. We propose to use heuristics-based techniques, namely the A* algorithm, both to guide the search without constructing the complete transition system, and to provide minimal counterexamples. We have realized a prototype tool to evaluate the methodology. Experiments we have conducted on processes of different size show the benefit from using our technique against building the whole state space, or applying some other methods
Rapid Parallelization by Collaboration
The widespread adoption of Chip Multiprocessors has renewed the emphasis on the use of parallelism to improve performance. The present and growing diversity in hardware architectures and software environments, however, continues to pose difficulties in the effective use of parallelism thus delaying a quick and smooth transition to the concurrency era. In this document, we describe the research being conducted at the Computer Science Department at Columbia University on a system called COMPASS that aims to simplify this transition by providing advice to programmers considering parallelizing their code. The advice proffered to the programmer is based on the wisdom collected from programmers who have already parallelized some code. The utility of COMPASS rests, not only on its ability to collect the wisdom unintrusively but also on its ability to automatically seek, find and synthesize this wisdom into advice that is tailored to the code the user is considering parallelizing and to the environment in which the optimized program will execute in. COMPASS provides a platform and an extensible framework for sharing human expertise about code parallelization -- widely and on diverse hardware and software. By leveraging the "Wisdom of Crowds" model which has been conjunctured to scale exponentially and which has successfully worked for Wikis, COMPASS aims to enable rapid parallelization of code and thus continue to extend the benefits for Moore's law scaling to science and society
Europe's governance in crises: politicisation and adaptation
Sack D. Europe's governance in crises: politicisation and adaptation. Working Paper Series ‘Comparative Governance’ . Vol 4. Bielefeld: Universität Bielefeld. Arbeitsgebiet Vergleichende Politikwissenschaft; 2020
Development Process for Multi-Disciplinary Embedded Control Systems
This report contains the progress report for the qualification exam for Industrial PhD student Sune Wolff. Initial work on describing a development process for multi-disciplinary systems using collaborative modelling and co-simulation is described
Optimal Stateless Model Checking under the Release-Acquire Semantics
We present a framework for the efficient application of stateless model
checking (SMC) to concurrent programs running under the Release-Acquire (RA)
fragment of the C/C++11 memory model. Our approach is based on exploring the
possible program orders, which define the order in which instructions of a
thread are executed, and read-from relations, which specify how reads obtain
their values from writes. This is in contrast to previous approaches, which
also explore the possible coherence orders, i.e., orderings between conflicting
writes. Since unexpected test results such as program crashes or assertion
violations depend only on the read-from relation, we avoid a potentially
significant source of redundancy. Our framework is based on a novel technique
for determining whether a particular read-from relation is feasible under the
RA semantics. We define an SMC algorithm which is provably optimal in the sense
that it explores each program order and read-from relation exactly once. This
optimality result is strictly stronger than previous analogous optimality
results, which also take coherence order into account. We have implemented our
framework in the tool Tracer. Experiments show that Tracer can be significantly
faster than state-of-the-art tools that can handle the RA semantics.Comment: Accepted paper in OOPSLA'1
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