The avatars of a package for calendars in ada

This paper shows the evolution of components for calendars written in Ada, starting from a classic form and evolving by the effect of some choices of software engineering. The first choice is to specify separate components when they do not have to be coupled in only one. This choice transforms a one-component form into a three-component one. The second choice is to hide all entities that are not required by the modelling of the real world. This choice modifies many declarations into forms which are complex to specify but which introduce no additional complexity to the user. In addition to the development of this component for the current legal calendar, it is indicated how others can be defined and converted from any one to the other. The design of a deep automatic test is illustrated. Finally, the paper illustrates how the new features of Ada-95 can be used to specify these calendars in another form, but which is not essentially different from the Ada-83 text.     

A complete axiomatic semantics of spawning

Summary In modern imperative languages there are two commonly occurring ways to activate concurrently running tasks,splitting (cobegin...coend) andspawning. The programming language Ada makes use of both forms of task activation. We present a formal system for verifying partial correctness specifications of Ada tasks activated by spawning. The system is based upon a view of tasks as histories of events. We show how the mindset of splitting may be applicable when developing a formal system for reasoning about spawning. The resultant proof system is compositional, and a robust extension of partial correctness proof systems for sequential constructs. A transition model is given for spawning, and the proof system is proven complete in the sense of Cook [10] relative to this model, under certain reasonable assumptions. The specific proof rules given apply to a subset of Ada without real-time and distributed termination. Our approach to task verification applies to other imperative languages besides Ada, and the essential parts of our methodology are applicable to other formal systems besides those based on partial correctness reasoning. Sigurd Meldal is professor of informatics at the University of Bergen. He is interested in techniques and tools based on formal methods for development of concurrent software. His current foci are the investigation of algebraic approaches to nondeterminism, and the participation in the design of a concurrent specification, prototyping and implementation language. The latter supplements formal proof with support for run time control of consistency between concurrent systems as specified and as implemented. Meldal received his cand. real. (1982) and dr. scient. (1986) degrees in informatics from the University of Oslo.This research was supported by a grant from the Norwegian Research Council for Science and the Humanities, by the Defense Advanced Research Projects Agency/Information Systems Technology Office under the office of Naval Research contract N00014-90-J1232, by the Air Force Office of Scientific Research under Grant AFOSR83-0255 and by a Fulbright Scholarship from the US Educational Foundation in Norway     

Real-time interrupt handling in Ada

The Ada? programming language defines the semantics of interrupt handling as part of the tasking mechanism, making it possible to construct implementation-independent interrupt handlers. However, for the Ada mechanism to be effective, an implementation must provide support not specified by the Ada standard, such as for initializing hardware interrupting devices, handling unexpected interrupts and optimizing for real-time performance constraints. This paper analyses some of the constraints that efficient interrupt support places on an implementation. It develops a model for the interaction between interrupt hardware and Ada tasks and describes optimizations for Ada interrupt handlers. Implementation issues, including task priorities and task termination for interrupt handlers, are discussed in detail.     

The suitability for master/slave concurrency of concurrent euclid,ada and modula

The suitability of Concurrent Euclid, Ada and Modula for a special form of asynchronous concurrency, called master/slave concurrency, is investigated. No language is ideal, with Concurrent Euclid and Modula having major drawbacks. The conclusion lists the features desirable in a language for master/slave concurrency.     

Message passing communication versus procedure call communication

Communication by message passing or by procedure calls in one of the key issues when discussing languages for multiprogramming. The two languages Platon and Concurrent Pascal represent the different approaches which are contrasted by presenting a few programs written in both languages.     

A case study of different task implementations for multioutput stages in non-trivial parallel pipeline applications

Task-based libraries, such as Intel’s Threading Building Blocks (TBB), are promising tools that help programmers to develop parallel code in a productive way, thanks to high-level constructors which simplify the chore of efficiently exploiting system resources. In this paper we focus on one type of task parallelism, pipeline parallelism, which is becoming an increasingly popular parallel programming pattern for streaming applications in the domain of digital signal processing, graphics, compression and encryption. Specifically, TBB provides a high-level template to express pipeline parallelism, but it is limited to representing simple pipeline structures. We address the issue of non-trivial parallel pipeline structures in which one or more stages in the pipeline have more items leaving than arriving, a problem for which the current TBB pipeline template does not provide support. In this work, we describe a new Multioutput filter that we have incorporated into the TBB pipeline framework to deal with these multioutput stages. Using real world streaming applications from different computational domains (dedup and scenerecog), we also compare the performance of our implementation using the Multioutput filter in the TBB pipeline template to other more complex TBB task-based implementations that only use the standard filters. We also develop new analytical models for each implementation to better understand the resources utilization in each case. Performance evaluation and analysis shows that the implementation based on the Multioutput filter outperforms the other solutions because: it promotes finer task parallelism, which is more suited to the TBB task-stealing mechanism in order to better exploit the resources; and it also reduces the overheads related to memory and task management.     

New conditions for synchronization in dynamical communication networks

This paper investigates synchronization in a typical multi-agent system in which the communication network changes according to the system state. Through building new relationships between a matrix and its associated graph and estimating the diameter of the communication network, we prove that synchronization can be achieved if the speed of agents is bounded by O(n^−β), where n is the number of agents and β is bounded by a constant independent of n, which is much better than the existing bound O(n⁻ⁿ). Some simulations are provided to illustrate the theoretical results.     

Comparing ada and FORTRAN lines of code: Some experimental results

This paper presents the results of a study comparing pairs of functionally equivalent programs written in the FORTRAN and Ada languages. We found the Ada programs to require more lines of code than their functionally equivalent FORTRAN counterparts. However, we also observed that the overhead for Ada diminishes as program size increases. Our limited data suggested that there may be a cross-over point beyond which the size of an Ada program would be smaller than a functionally equivalent FORTRAN program. We explore some of the reasons for these economies of scale when using Ada. The implications of our findings on software cost estimating are also discussed.     

A performance study of multiprocessor task scheduling algorithms

Multiprocessor task scheduling is an important and computationally difficult problem. A large number of algorithms were proposed which represent various tradeoffs between the quality of the solution and the computational complexity and scalability of the algorithm. Previous comparison studies have frequently operated with simplifying assumptions, such as independent tasks, artificially generated problems or the assumption of zero communication delay. In this paper, we propose a comparison study with realistic assumptions. Our target problems are two well known problems of linear algebra: LU decomposition and Gauss–Jordan elimination. Both algorithms are naturally parallelizable but have heavy data dependencies. The communication delay will be explicitly considered in the comparisons. In our study, we consider nine scheduling algorithms which are frequently used to the best of our knowledge: min–min, chaining, A^*, genetic algorithms, simulated annealing, tabu search, HLFET, ISH, and DSH with task duplication. Based on experimental results, we present a detailed analysis of the scalability, advantages and disadvantages of each algorithm.

Multimedia group and inter-stream synchronization techniques: A comparative study

This paper presents the most comprehensive analysis and comparison of the most-known multimedia group and inter-stream synchronization approaches. Several types of multimedia synchronization are identified but only inter-stream and group synchronization algorithms are considered. This is the first survey including group synchronization techniques. A classification of the main synchronization techniques included in most of the analyzed algorithms complements the paper. Finally, a table is presented summarizing the main characteristics of each analyzed algorithm according to those techniques and other critical issues.     

Factors limiting the development of task analysis

Abstract

This paper sets out to summarize the current status of task analysis. There is a lack of consensus over terminology. Approaches have emerged from different theoretical and methodological sources and have been developed in different applications contexts. This has lead to a great variety of approaches, which have been used at different stages of analysis and have been given various names. Strategies for improving this situation are suggested, as are criteria for assessing approaches. The need to progress towards a well-established methodology is evident, but it is seen as a long-term goal.     

The roles of group potency and information and communication technologies in the relationship between task conflict and team effectiveness: A longitudinal study

The effects of task conflict on group effectiveness are far from conclusive. In order to further clarify this relationship, a contingency approach has been suggested. In this context, the present study examines the roles of group potency and information and communication technologies (ICTs) in the relationship between task conflict and team effectiveness. The study involved 44 groups of 4 members each, working in two communication media. Twenty-two groups worked in a face-to-face condition, and the other 22 groups worked in a computer-mediated communication condition. The groups developed a project during four weekly sessions over a one-month period. The results showed that group potency moderated the relationship between task conflict and group effectiveness. However, the communication medium did not play a moderator role in these relationships.     

A two-stage heuristic for multi-activity and task assignment to work shifts

The multi-activity assignment problem consists of assigning interruptible activities to given work shifts so as to match as much as possible for each activity a demand curve in function of time. In this paper we consider an extension to this problem, called the multi-activity and task assignment problem, that additionally considers the assignment of uninterruptible pieces of work, called tasks. These possess properties such as worker qualifications, time windows for completion, fixed lengths and precedence relationships. We propose a mixed-integer programming formulation and a two-stage method to solve this problem. The first stage consists of an approximation mixed-integer programming model to assign tasks approximately taking into account the activities and the second involves a column generation heuristic for assigning activities and reassigning tasks at the same time. We suggest four different strategies for reassigning tasks. We conducted extensive computational tests on randomly generated instances in order to validate our method and to compare the various strategies. One strategy proved universally best when compared to the other three policies.     

A comparative study of mobile map displays in a geographic orientation task

In an ergonomic experiment, different mobile map displays were compared in a simulated geographical orientation task. Subjects had to cross mazes while the corresponding maps were presented on a hand-held display, two helmet-mounted displays (a retinal scanning and a liquid crystal display) or on paper. The simulated mazes were projected on a backlit screen and the subjects could cross them using a joystick. The displays were compared with regard to subjects' speed when crossing the mazes, experienced task difficulty, visual fatigue and simulator sickness. The results show that speed was lowest with the paper map and experienced task difficulty was highest, whereas no significant differences were found between the electronic displays. Visual fatigue and simulator sickness were low and no significant differences were observed between all displays. The conclusion is drawn that all electronic map displays can be used for short time periods (15 – 30 minutes); however, long term effects have to be analysed in future experimental studies.     

A comparative study of mobile map displays in a geographic orientation task

In an ergonomic experiment, different mobile map displays were compared in a simulated geographical orientation task. Subjects had to cross mazes while the corresponding maps were presented on a hand-held display, two helmet-mounted displays (a retinal scanning and a liquid crystal display) or on paper. The simulated mazes were projected on a backlit screen and the subjects could cross them using a joystick. The displays were compared with regard to subjects' speed when crossing the mazes, experienced task difficulty, visual fatigue and simulator sickness. The results show that speed was lowest with the paper map and experienced task difficulty was highest, whereas no significant differences were found between the electronic displays. Visual fatigue and simulator sickness were low and no significant differences were observed between all displays. The conclusion is drawn that all electronic map displays can be used for short time periods (15 - 30 minutes); however, long term effects have to be analysed in future experimental studies.     

一个多串口多线程数据采集系统软件的设计与实现

本文着重探讨用多线程并行的方式通过多个串口进行并行通信。使用多线程进行串行通信的文献已有一些,但都没涉及到多个串口并行的情况。本文介绍的多串口多线程通信方法,使多个串口并行通信,从而实现大规模的数据采集与高速数据传输操作。     

Benchmark-problem instances for static scheduling of task graphs with communication delays on homogeneous multiprocessor systems

Scheduling program tasks on processors is at the core of the efficient use of multiprocessor systems. Most task-scheduling problems are known to be NP-Hard and, thus, heuristics are the method of choice in all but the simplest cases. The utilization of acknowledged sets of benchmark-problem instances is essential for the correct comparison and analysis of heuristics. Yet, such sets are not available for several important classes of scheduling problems, including multiprocessor scheduling problem with communication delays (MSPCD) where one is interested in scheduling dependent tasks onto homogeneous multiprocessor systems, with processors connected in an arbitrary way, while explicitly accounting for the time required to transfer data between tasks allocated to different processors. We propose test-problem instances for the MSPCD that are representative in terms of number of processors, type of multiprocessor architecture, number of tasks to be scheduled, and task graph characteristics (task execution times, communication costs, and density of dependencies between tasks). Moreover, we define our task-graph generators in a way appropriate to ensure that the corresponding problem instances obey the theoretical principles recently proposed in the literature.     

实时控制网动态通信频度研究

基于控制系统对通信要求的现实,提出对控制网采取动态通信频度。并给出动态通信频度的一种实现方法,结合竞争使用信道和通信调度,动态跟随通信需求频度,提高通信实时性,提高通信实际效能。     

A comparative study of access topologies for chip-level address-event communication channels

We examine channel access algorithms and circuits for intra and inter chip communication channels. Classical access techniques such as arbitration, scanning, ALOHA, and priority encoding are compared by assessing throughput, latency, and power consumption. Our results provide guidance in the design of bio-inspired networks of processors, for efficient transmission of information with limited power consumption and reduced latency.