Mutual exclusion

Almost all computers today operate as part of a network, where they assist people in coordinating actions. Sometimes what appears to be a single computer is actually a network of cooperating computers; e.g., some supercomputers consist of many processors operating in parallel and exchanging synchronization signals. One of the most fundamental requirements in all these systems is that certain operations be indivisible: the steps of one must not be interleaved with the steps of another. Two approaches were designed to implement this requirement, one based on central locks and the other on distributed order tickets. Practicing scientists and engineers need to come to be familiar with these methods

Implementation of mutual exclusion in VHDL

In VHDL it is difficult to implement mutual exclusion at an abstract level since atomic actions are required. A local status model and an arbiter model are presented to achieve mutual exclusion in VHDL. Shared data, protected by a mutual exclusion mechanism, cannot be modelled as a simple, resolved VHDL signal since no resolution function is able to return the correct value. By changing the signal type to a special record type this problem can be solved, using the arbiter model. The specification language Task Level VHDL (TLVHDL) has been developed to specify communication and synchronization mechanisms at an abstract level. In TLVHDL the abovementioned problems are not encountered. A back end compiler converts the abstract TLVHDL description into a VHDL specification, according to a chosen mutual exclusion model. All modifications are handled by the computer and are of no concern to the designer

EOS: A project to investigate the design and construction of real-time distributed embedded operating systems

The EOS project is investigating the design and construction of a family of real-time distributed embedded operating systems for reliable, distributed aerospace applications. Using the real-time programming techniques developed in co-operation with NASA in earlier research, the project staff is building a kernel for a multiple processor networked system. The first six months of the grant included a study of scheduling in an object-oriented system, the design philosophy of the kernel, and the architectural overview of the operating system. In this report, the operating system and kernel concepts are described. An environment for the experiments has been built and several of the key concepts of the system have been prototyped. The kernel and operating system is intended to support future experimental studies in multiprocessing, load-balancing, routing, software fault-tolerance, distributed data base design, and real-time processing

A network flow model for load balancing in circuit-switched multicomputers

In multicomputers that utilize circuit switching or wormhole routing, communication overhead depends largely on link contention - the variation due to distance between nodes is negligible. This has a major impact on the load balancing problem. In this case, there are some nodes with excess load (sources) and others with deficit load (sinks) and it is required to find a matching of sources to sinks that avoids contention. The problem is made complex by the hardwired routing on currently available machines: the user can control only which nodes communicate but not how the messages are routed. Network flow models of message flow in the mesh and the hypercube were developed to solve this problem. The crucial property of these models is the correspondence between minimum cost flows and correctly routed messages. To solve a given load balancing problem, a minimum cost flow algorithm is applied to the network. This permits one to determine efficiently a maximum contention free matching of sources to sinks which, in turn, tells one how much of the given imbalance can be eliminated without contention

SOLVING CONTEST PROBLEMS \ud VIA FORMAL PROGRAM VERIFICATION\ud

The interface between mathematics and computer science is many-sided. In particular, E.W. Dijkstra promoted a special “computer science” approach to mathematics problem solving. The approach combines a heuristic algorithm design and rigorous mathematical proof of algorithm correctness (in style of A. Hoare and R. Floyd). The paper sketches two problems of this kind in a form of tutorials for undergraduate students that are interested in different programming contests (like ACM International Collegiate Programming Contests). These tutorials took place at Novosibirsk State University in years 2005–2008. The paper also dioceses some direction for further research that emerge from the problems

Parallel asynchronous label correcting methods for shortest paths

Caption title. "May 1994 (revised October 1994)."Includes bibliographical references (p. 24-25).Supported by the National Science Foundation. 9108058-CCR 9221293-INT 9300494-DMIDimitri P. Bertsekas, Francesca Guerriero and Roberto Musmanno

A Survey and analysis of algorithms for the detection of termination in a distributed system

This paper looks at algorithms for the detection of termination in a distributed system and analyzes them for effectiveness and efficiency. A survey is done of the published algorithms for distributed termination and each is evaluated. Both centralized distributed systems and fully distributed systems are reviewed. The algorithms are analyzed for the overhead and conclusions are made about the situations in which they can be used, i.e. an operating system, a real-time system, or a user application. An original algorithm is presented for the asynchronous case with first-in-first-out message ordering. It allows any process to initiate detection of termination and makes use of multiple tokens

Mobile Tour Assistant for Malaysia

Malaysia's tourism industry has seen a rapid growth rate for the past years, and played a significant role in the development of the country's economy. 2007 is a special year for Malaysian tourism since it is called the "Visit Malaysia" year in celebration of 50 years of Independence. Information Technology has made remarkable contributions to the growth of tourism industry in Malaysia. Its efforts to promote tourism range from websites providing information to systems to service tourists. However, while countries with well-developed tourism industry like France and Hong Kong have developed comprehensive tour assistant packages for tourists, Malaysia is yet to do so. Thus, a comprehensive mobile tour package is needed for Malaysia. The objective of the project is to develop a well-designed tour assistant running on PDAs which makes use of current trends in mobile applications such as the adoption of AI technique in scheduling. Due to time and resource constraints, the project focuses on areas within and around Kuala Lumpur and targets on short-stay and transit tourists. Going through a thorough literature review and following the waterfall methodology, the project has successfully developed a full package of mobile tour assistant including the back end and front end. The project also makes contribution to creatively applying Genetic Algorithm, an AI technique in plan auto-scheduling. The author hopes that the package will be of high commercial value and contribute significantly to boosting Malaysia's tourism