Concurrency

A API JDBC permite aos programas Java manipularem dados de uma base de dados. No entanto, a de�ni�c~ao da API n~ao prev^e uma utiliza�c~ao concorrente dos seus servi�cos, n~ao �e por isso poss��vel partilhar objectos JDBC em seguran�ca entre threads. Neste documento �e descrita uma implementa�c~ao concorrente da interface ResultSet. Esta interface �e utilizada para ler ou modi�car linhas do resultado da execu�c~ao de uma instru�c~ao SQL. O driver JDBC foi criado para SQL Server 2008. De modo a avaliar o desempenho da solu�c~ao desenvolvida foram realizados testes de desempenho comparando-a com a implementa�c~ao do driver da Microsoft, em que se criou um ResultSet por thread. Os resultados mostraram que a ideia desenvolvida produz um aumento de desempenho em ambientes multithreaded.

Article, or exactly - chapter in the book - describes many multiprocessor architectures proposed and discovered by numerous researchers. This comprehensive survey begins on general remarks about images and processes necessary during their enhancement, analysis, and recognition. Next many methods and approaches used for parallel processing and concurrent analysis of the images are presented, discussed and assessed.

Wait-free synchronization has been recognized in the literature as an effective concurrent programming technique. The concurrent programming community, however, has been slow to adopt this technique. This paper addresses the practical application of wait-free synchronization in the design of distributed applications. In this paper, we present an implementation of a server that uses wait-free synchronization. The resulting code is more easily seen to be fault tolerant. The performance analysis of the wait-free synchronization server outperformed a server that uses traditional locking techniques. This practical demonstration of the benefits of wait-free synchronization should help foster its adoption in the development of distributed applications.

ABSTRACT: For Romania, who has limited resources of capital on internal plan, foreign investments represent more than a necessity, foreign capital, besides the contribution to supplementation of financial resources of the country, having support role for inevitable ...

Computer modeling and simulation is the art of bringing to life systems and behaviors that otherwise are prohibitively expensive, unethical, or just impossible to build. This article explains how to use SimPy, a Python-based discrete event simulation framework.

The embedded software industry is in the midst of a major revolution. Tremendous amount of new development lies ahead. This new software needs an actual architecture that is safer, more extensible, and easier to understand than the usual "shared-state concurrency and blocking" based on a traditional Real-Time Operating System (RTOS). Quantum Leaps' QP™ real-time embedded frameworks (RTEFs) and the QM™ model-based design (MBD) tool provide such a modern, event-driven architecture based on active objects (actors), hierarchical state machines (UML statecharts), software tracing, unit testing, model-based engineering and automatic code generation.

Databases are replicated to improve performance and availability. The notion of correctness that has commonly been adopted for concurrent access by transactions to shared, possibly replicated, data is serializability. However, serializability may be impractical in high-performance applications since it imposes too stringent a restriction on concurrency. When serializability is relaxed, the integrity constraints describing the data may be violated. By allowing bounded violations of the integrity constraints, however, we are able to increase the concurrency of transactions that execute in a replicated environment. In this article, we introduce the notion of an N-ignorant transaction, which is a transaction that may be ignorant of the results of at most N prior transactions, which is a transaction that may be ignorant of the results of at most N prior transactions. A system in which all transactions are N-ignorant can have an N + 1-fold increase in concurrency over serializable systems...

Mata kuliah sistem operasi merupakan salah satu mata kuliah wajib yang harus diajarkan kepada mahasiswa yang mengambil jurusan / program studi teknik informatika / sistem informasi / teknologi informasi. Mata kuliah ini memperkenalkan kepada mahasiswa mengenai konsep sistem operasi, jenis-jenis sistem operasi yang digunakan dalam kehidupan sehari-hari, layanan-layanan umum yang dimiliki oleh sistem operasi, dan mempelajari teknik dan algoritma yang digunakan dalam penerapan / pengelolaan layanan di sistem operasi. Sistem operasi adalah suatu program yang bertindak sebagai perantara antara user, program aplikasi dan perangkat keras. Beberapa layanan umum yang dimiliki oleh sistem operasi antara lain manajemen penjadwalan proses, manajemen sumber daya (resource), manajemen
memori, sistem berkas, manajenen jaringan, manajemen keamanan, manajemen penyimpanan, dan manajemen perangkat masukan-keluaran. Dalam penelitian kali ini, pembahasan akan dikerucutkan ke dalam salah satu layanan Sistem Operasi yaitu manajemen penjadwalan proses. Salah satu materi turunan dari manajemen proses yang sulit untuk dipahami oleh mahasiswa adalah Concurrency. Secara umum concurrency merupakan proses-proses (lebih dari satu proses) yang terjadi pada saat bersamaan. Beberapa algoritma yang digunakan dalam penerapan concurrency pada manajemen proses antara lain Dining Philosophers, Banker Algorithm, Producer-Consumer, dan Readers-Writers. Penjelasan terkait keempat algoritma tersebut membutuhkan logika dan tingkat keseriusan yang tinggi. Sayangnya tidak semua mahasiswa mampu untuk mempertahankan konsentrasinya dalam waktu yang lama untuk mempelajari alur logika dari keempat algoritma tersebut. Berdasarkan uraian di atas, penulis ingin merancang suatu perangkat lunak yang mampu untuk mensimulasikan keempat algoritma tersebut ke dalam bentuk media pembelajaran berbasis multimedia sehingga diharapkan akan meningkatkan daya tarik dan daya tangkap dari mahasiswa yang mempelajarinya.

In this paper, we describe a component-based software architecture for the Internet of Things in which proxies for Things and services that we call "accessors" interact with one another under a concurrent, time-stamped, discrete-event (DE) semantics. These proxies are analogous to web pages, which proxy a cloud-based service such as a bank, but instead of being designed to interface those services with humans, accessors are designed to interface services and Things with other services and Things. A deterministic DE semantics is combined with a widely used pattern for handling network interactions that we call asynchronous atomic callbacks (AACs). AAC enables many concurrent pending requests to be active at once without blocking and without the treacherous concurrency pitfalls of threads. In effect, our architecture combines AAC with actors where the actor model has been endowed with a temporal semantics. We show how this architecture can leverage the previously reported secure swarm toolkit (SST) to achieve state-of-the-art authentication, authorization, and encryption of interactions across networks.

Component-based software development offers a promising solution for taming the complexity found in today's distributed applications. Today's and future distributed software systems will certainly require combining heterogeneous software components that are geographically dispersed. For the successful deployment of such a software system, it is necessary that its realization, based on assembling heterogeneous components, not only meets the functional requirements, but also satisfies the non-functional criteria such as the desired quality of service (QoS). In this paper, a framework based on the notions of a meta-component model, a generative domain model and QoS parameters is described. A formal specification based on two-level grammar is used to represent these notions in a tightly integrated way so that QoS becomes a part of the generative domain model. A simple case study is described in the context of this framework. Copyright © 2002 John Wiley & Sons, Ltd.

This thesis explores how scientific applications, which are based upon short jobs (seconds and minutes) can capitalize upon the idle workstations of a Campus-Grid. These resources are donated on a voluntary basis, and consequently, the Campus-Grid is constantly adapting and the availability of workstations changes. Typically, to utilize these resources a Condor system or equivalent would be used. However, such systems are designed with different trade-offs and incentives in mind and therefore do not provide ...

Los computadores procesan información y toman decisiones. Hasta hace poco, las decisiones que tomaban no eran complejas, pero debido a los incesantes avances tecnológicos que se producen, los sistemas basados en inteligencia artificial están logrando niveles de competencia en la toma de decisiones que en muchos contextos igualan o superan a las personas. Se trata de sistemas autónomos de decisión que, si bien pueden aumentar la capacidad y eficiencia de las personas en sus ámbitos de actuación, también podrían sustituirlas, algo que preocupa al conjunto de la sociedad. Evitar disfunciones en estos sistemas es un objetivo social, científico y tecnológico prioritario, que exige contar con modelos teóricos, que recojan toda la riqueza y variedad de los problemas de decisión, que definan precisamente los elementos que los caracterizan y que atiendan los planteamientos éticos que deben guiar su funcionamiento. Este artículo describe en sendas secciones cada uno de estos aspectos.

Computers process information and make decisions. Until recently, the decisions they made were not complex, but due to the incessant technological advances that occur, systems based on Artificial Intelligence are achieving levels of competence in decision-making that in many contexts equal or exceed people. These are Autonomous Decision Systems that, although they can increase the capacity and efficiency of people in their fields of action, could also replace them, something that worries the whole of Society. Avoiding missfunctions in these systems is a priority social, scientific and technological objective, which requires having theoretical models that collect all the richness and variety of decision problems, that define precisely the elements that characterize them and that address the ethical approaches which should guide its operation. This paper describes each of these aspects in a separate section.

In this paper we survey, consolidate, and present the state of the art in distributed database concurrency control. The heart of our analysts is a decomposition of the concurrency control problem into two major subproblems: read-write and write-write synchronization. We describe a series ...