Improving the efficiency of nondeterministic indepemndent and-parallel systems

We present the design and implementation of the and-parallel component of ACE. ACE is a computational model for the full Prolog language that simultaneously exploits both or-parallelism and independent and-parallelism. A high performance implementation of the ACE model has been realized and its performance reported in this paper. We discuss how some of the standard problems which appear when implementing and-parallel systems are solved in ACE. We then propose a number of optimizations aimed at reducing the overheads and the increased memory consumption which occur in such systems when using previously proposed solutions. Finally, we present results from an implementation of ACE which includes the optimizations proposed. The results show that ACE exploits and-parallelism with high efficiency and high speedups. Furthermore, they also show that the proposed optimizations, which are applicable to many other and-parallel systems, significantly decrease memory consumption and increase speedups and absolute performance both in forwards execution and during backtracking

A proposal for a flexible scheduling and memory management scheme for non-deterministic, andparallel execution of logic programs

In this paper, we examine the issue of memory management in the parallel execution of logic programs. We concentrate on non-deterministic and-parallel schemes which we believe present a relatively general set of problems to be solved, including most of those encountered in the memory management of or-parallel systems. We present a distributed stack memory management model which allows flexible scheduling of goals. Previously proposed models (based on the "Marker model") are lacking in that they impose restrictions on the selection of goals to be executed or they may require consume a large amount of virtual memory. This paper first presents results which imply that the above mentioned shortcomings can have significant performance impacts. An extension of the Marker Model is then proposed which allows flexible scheduling of goals while keeping (virtual) memory consumption down. Measurements are presented which show the advantage of this solution. Methods for handling forward and backward execution, cut and roll back are discussed in the context of the proposed scheme. In addition, the paper shows how the same mechanism for flexible scheduling can be applied to allow the efficient handling of the very general form of suspension that can occur in systems which combine several types of and-parallelism and more sophisticated methods of executing logic programs. We believe that the results are applicable to many and- and or-parallel systems

Automated test of evolving software

A thesis submitted to the University of Luton, in partial fulfilment of the requirements for the degree of Doctor of PhilosophyComputers and the software they run are pervasive, yet released software is often unreliable, which has many consequences. Loss of time and earnings can be caused by application software (such as word processors) behaving incorrectly or crashing. Serious disruption can occur as in the l4th August 2003 blackouts in North East USA and Canadal, or serious injury or death can be caused as in the Therac-25 overdose incidents. One way to improve the quality of software is to test it thoroughly. However, software testing is time consuming, the resources, capabilities and skills needed to carry it out are often not available and the time required is often curtailed because of pressures to meet delivery deadlines3. Automation should allow more thorough testing in the time available and improve the quality of delivered software, but there are some problems with automation that this research addresses. Firstly, it is difficult to determine ifthe system under test (SUT) has passed or failed a test. This is known as the oracle problem4 and is often ignored in software testing research. Secondly, many software development organisations use an iterative and incremental process, known as evolutionary development, to write software. Following release, software continues evolving as customers demand new features and improvements to existing ones5. This evolution means that automated test suites must be maintained throughout the life ofthe software. A contribution of this research is a methodology that addresses automatic generation of the test cases, execution of the test cases and evaluation of the outcomes from running each test. "Predecessor" software is used to solve the oracle problem. This is software that already exists, such as a previous version of evolving software, or software from a different vendor that solves the same, or similar, problems. However, the resulting oracle is assumed not be perfect, so rules are defined in an interface, which are used by the evaluator in the test evaluation stage to handle the expected differences. The interface also specifies functional inputs and outputs to the SUT. An algorithm has been developed that creates a Markov Chain Transition Matrix (MCTM) model of the SUT from the interface. Tests are then generated automatically by making a random walk of the MCTM. This means that instead of maintaining a large suite of tests, or a large model of the SUT, only the interface needs to be maintained. 1) NERC Steering Group (2004). Technical Analysis ofthe August 14,2003, Blackout: What Happened, Why, and What Did We Learn? July 13th 2004. Available from: ftp:/ /www.nerc.com/pub/sys/all_ updl/docslblackoutINERC ]inatBlackout_Report _ 07_13_ 04.pdf 2) Leveson N. G., Turner C. S. (1993) An investigation of the Therac-25 accidents. IEEE Computer, Vo126, No 7, Pages 18-41. 3) LogicaCMG (2005) Testing Times for Board Rooms. Available from http://www.logicacmg.com/pdf/trackeditestingTimesBoardRooms.pdf 4) Bertolino, A. (2003) Software Testing Research and Practice, ASM 2003, Lecture Notes in Computer Science, Vol 2589, Pages 1-21. 5) Sommerville, 1. (2004) Software Engineering, 7th Edition. Addison Wesley. ISBN 0-321-21026-3

Programming models for many-core architectures: a co-design approach

Common many-core processors contain tens of cores and distributed memory. Compared to a multicore system, which only has a few tightly coupled cores sharing a single bus and memory, several complex problems arise. Notably, many cores require many parallel tasks to fully utilize the cores, and communication happens in a distributed and decentralized way. Therefore, programming such a processor requires the application to exhibit concurrency. In contrast to a single-core application, a concurrent application has to deal with memory state changes with an observable (non-deterministic) intermediate state. The complexity introduced by these problems makes programming a many-core system with a single-core-based programming approach notoriously hard.\ud \ud The central concept of this thesis is that abstractions, which are related to (many-core) programming, are structured in a single platform model. A platform is a layered view of the hardware, a memory model, a concurrency model, a model of computation, and compile-time and run-time tooling. Then, a programming model is a specific view on this platform, which is used by a programmer. In this view, some details can be hidden from the programmer's perspective, some details cannot. For example, an operating system presents an infinite number of parallel virtual execution units to the application whilst it hides details regarding scheduling. On the other hand, a programmer usually has balance workload among threads by hand.\ud \ud This thesis presents modifications to different abstraction layers of a many-core architecture, in order to make the system as a whole more efficient, and to reduce the programming complexity. These modifications influence other abstractions in the platform, and especially the programming model. Therefore, this thesis applies co-design on all models. Notably, co-design of the memory model, concurrency model, and model of computation is required for a scalable implementation of lambda-calculus. Moreover, only the combination of requirements of the many-core hardware from one side and the concurrency model from the other leads to a memory model abstraction. Hence, this thesis shows that to cope with the current trends in many-core architectures from a programming perspective, it is essential and feasible to inspect and adapt all abstractions collectively

Research and Technology, 1989

Selected research and technology activities at Ames Research Center, including the Moffett Field site and the Dryden Flight Research Facility, are summarized. These accomplishments exemplify the Center's varied and highly productive research efforts for 1989

Astronautics and aeronautics, 1978: A chronology

This is the 18th in a series of annual chronologies of significant events in the fields of astronautics and aeronautics. Events covered are international as well as national and political as well as scientific and technical. This series is a reference work for historians, NASA personnel, government agencies, congressional staffs, and the media

Spinoff 2013

Topics covered include: Innovative Software Tools Measure Behavioral Alertness; Miniaturized, Portable Sensors Monitor Metabolic Health; Patient Simulators Train Emergency Caregivers; Solar Refrigerators Store Life-Saving Vaccines; Monitors Enable Medication Management in Patients' Homes; Handheld Diagnostic Device Delivers Quick Medical Readings; Experiments Result in Safer, Spin-Resistant Aircraft; Interfaces Visualize Data for Airline Safety, Efficiency; Data Mining Tools Make Flights Safer, More Efficient; NASA Standards Inform Comfortable Car Seats; Heat Shield Paves the Way for Commercial Space; Air Systems Provide Life Support to Miners; Coatings Preserve Metal, Stone, Tile, and Concrete; Robots Spur Software That Lends a Hand; Cloud-Based Data Sharing Connects Emergency Managers; Catalytic Converters Maintain Air Quality in Mines; NASA-Enhanced Water Bottles Filter Water on the Go; Brainwave Monitoring Software Improves Distracted Minds; Thermal Materials Protect Priceless, Personal Keepsakes; Home Air Purifiers Eradicate Harmful Pathogens; Thermal Materials Drive Professional Apparel Line; Radiant Barriers Save Energy in Buildings; Open Source Initiative Powers Real-Time Data Streams; Shuttle Engine Designs Revolutionize Solar Power; Procedure-Authoring Tool Improves Safety on Oil Rigs; Satellite Data Aid Monitoring of Nation's Forests; Mars Technologies Spawn Durable Wind Turbines; Programs Visualize Earth and Space for Interactive Education; Processor Units Reduce Satellite Construction Costs; Software Accelerates Computing Time for Complex Math; Simulation Tools Prevent Signal Interference on Spacecraft; Software Simplifies the Sharing of Numerical Models; Virtual Machine Language Controls Remote Devices; Micro-Accelerometers Monitor Equipment Health; Reactors Save Energy, Costs for Hydrogen Production; Cameras Monitor Spacecraft Integrity to Prevent Failures; Testing Devices Garner Data on Insulation Performance; Smart Sensors Gather Information for Machine Diagnostics; Oxygen Sensors Monitor Bioreactors and Ensure Health and Safety; Vision Algorithms Catch Defects in Screen Displays; and Deformable Mirrors Capture Exoplanet Data, Reflect Lasers