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Um modelo de paralelismo de grao fino para objetos distribuidos; A fine-grain parallelism model for distributed objects

Avila, Rafael Bohrer
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
27.33%
Esta Dissertação apresenta um modelo de paralelismo de grão fino para utilização em aplicações baseadas em objetos distribuídos. A pesquisa é desenvolvida sobre o modelo de distribuição de objetos da linguagem DPC++, uma extensão de C++ concebida na Universidade Federal do Rio Grande do Sul. A motivação para o desenvolvimento deste modelo é a crescente disponibilidade de arquiteturas multiprocessadas e de tecnologias de comunicação de alto desempenho, o que permite o aproveitamento eficiente de um nível de concorrência de menor granularidade. O objetivo do trabalho é integrar de forma adequada e eficiente a utilização de tal nível de concorrência no modelo original de distribuição de objetos de DPC++, permitindo que as aplicações desenvolvidas com a linguagem possam explorar ao máximo o poder computacional oferecido pelas arquiteturas citadas. Como principais características, o modelo proposto apresenta a capacidade de concorrência entre os métodos de um mesmo objeto distribuído e a introdução de um mecanismo de sincronização baseado na semântica de monitores. Os resultados obtidos com a implementação de uma aplicação de geração de fractais de Mandelbrot demonstram que, em termos de desempenho...

Reusable aspect-oriented implementations of concurrency patterns and mechanisms

Sobral, João Luís Ferreira; Cunha, Carlos A.; Monteiro, Miguel Pessoa
Fonte: ACM Publicador: ACM
Tipo: Conferência ou Objeto de Conferência
Publicado em //2006 ENG
Relevância na Pesquisa
37.06%
In this paper, we present a collection of well-known high-level concurrency patterns and mechanisms, coded in AspectJ. We discuss benefits of these implementations relative to plain Java implementations of the same concerns. We detect benefits from using AspectJ in all the cases presented, in the form of higher modularity, reuse, understandability and unpluggability. For most of the implementations, two alternatives can be used: one based on traditional pointcut interfaces and one based on annotations.; Fundação para a Ciência e a Tecnologia (FCT) - PPC-VM Project POSI/CHS/47158/2002; Project SOFTAS (POSI/EIA/60189/2004).; Fundo Europeu de Desenvolvimento Regional (FEDER).

Data-centric concurrency control on the java programming language

Parreira, Daniel Luis Landeiroto
Fonte: Faculdade de Ciências e Tecnologia Publicador: Faculdade de Ciências e Tecnologia
Tipo: Dissertação de Mestrado
Publicado em //2013 ENG
Relevância na Pesquisa
37.33%
Dissertação para obtenção do Grau de Mestre em Engenharia Informática; The multi-core paradigm has propelled shared-memory concurrent programming to an important role in software development. Its use is however limited by the constructs that provide a layer of abstraction for synchronizing access to shared resources. Reasoning with these constructs is not trivial due to their concurrent nature. Data-races and deadlocks occur in concurrent programs, encumbering the programmer and further reducing his productivity. Even though the constructs should be as unobtrusive and intuitive as possible, performance must also be kept high compared to legacy lock-based mechanism. Failure to guarantee similar performance will hinder a system from adoption. Recent research attempts to address these issues. However, the current state of the art in concurrency control mechanisms is mostly code-centric and not intuitive. Its codecentric nature requires the specification of the zones in the code that require synchronization,contributing to the decentralization of concurrency bugs and error-proneness of the programmer. On the other hand, the only data-centric approach, AJ [VTD06], exposes excessive detail to the programmer and fails to provide complete deadlock-freedom. Given this state of the art...

Assessing Effectiveness and Cost-Effectiveness of Concurrency Reduction for HIV Prevention

Enns, Eva A.; Brandeau, Margaret L.; Igeme, Thomas K.; Bendavid, Eran
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/2011 EN
Relevância na Pesquisa
27.55%
We estimated the effectiveness and cost-effectiveness of changes in concurrent sexual partnerships in reducing the spread of HIV in sub-Saharan Africa. Using data from Swaziland, Tanzania, Uganda, and Zambia, we estimated country-specific concurrency behavior from sexual behavior survey data on the number of partners in the past 12 months, and we developed a network model to compare the impact of three behavior changes on the HIV epidemic: (1) changes in concurrent partnership patterns to strict monogamy; (2) partnership reduction among those with the greatest number of partners; and (3) partnership reduction among all individuals. We estimated the number of new HIV infections over ten years and the cost per infection averted. Given our assumptions and model structure, we find that reducing concurrency among high-risk individuals averts the most infections and increasing monogamy the least (11.7% versus 8.7% reduction in new infections, on average, for a 10% reduction in concurrent partnerships). A campaign that costs $1 per person annually is likely cost-saving if it reduces concurrency by 9% on average, given our baseline estimates of concurrency. In sensitivity analysis, the rank ordering of behavior change scenarios was unaffected by potential over-estimation of concurrency...

Sexual Concurrency among Young African American Women

Waldrop-Valverde, Drenna G.; Davis, Teaniese L.; Sales, Jessica M.; Rose, Eve S.; Wingood, Gina M.; DiClemente, Ralph J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.55%
Young African American women are disproportionately affected by HIV/AIDS, STIs, and engage in greater sexual concurrency than other race/ethnicities. It is important to evaluate behaviors and characteristics associated with the risk of sexual concurrency so interventions can target factors most likely to affect positive change. An emphasis on correlates of concurrency beyond individual-level factors has been suggested. The purpose of this study therefore was to identify individual- and partner-level characteristics associated with sexual concurrency among high-risk, young African American women. Data were collected from 570 African American adolescent women (aged 15–21) recruited from a STD clinic, a family planning clinic, and a teen clinic located in Atlanta, GA from March 2002 through August 2004. Logistic regression analysis was conducted in 2012 to evaluate correlates of sexual concurrency. Results show that almost one-quarter of participants reported sexually concurrent partnerships and 28.4% suspected male partner concurrency. Logistic regression results indicated the number of lifetime sexual partners and relationship factors were the primary contributors to engaging in concurrency in this sample. These findings suggest relationship factors may be important contributors to the prevalence of sexual concurrency among young African American women. Interventions targeted toward sexual health among young African American women may need to specifically address partner/relationship factors. Through these findings we hope to better understand sexual risk taking and develop strategies that would overcome barriers to existing interventions aimed at improving the sexual health outcomes of young...

Concurrency and Linear Hashing

Ellis, Carla Schlatter
Fonte: University of Rochester. Computer Science Department. Publicador: University of Rochester. Computer Science Department.
Tipo: Relatório
ENG
Relevância na Pesquisa
37.06%
Hashing has long been recognized as a fast method for accessing records by key in large relatively static databases. However. when the amount of data is likely to grow significantly, traditional hashing suffers from performance degradation and may eventually require rehashing all the records into a larger space. Recently, a number of techniques for dynamic hashing have appeared. In this paper, we present a solution to allow for concurrency in linear hash files that is based on locking protocols and minor modifications in the data structure. The problem of adapting this technique for use in a distributed system is also addressed.

Concurrency control overhead or closer look at blocking vs. nonblocking concurrency control mechanisms

Badal, Dusan Z.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Relatório Formato: 21 p. ; 28 cm.
EN_US
Relevância na Pesquisa
37.33%
This report has been published in the Proceedings of the Fifth Berkeley Conference on Distributed Data Management and Computer Networks.; In this paper we divide concurrency control (CC) mechanisms for distributed DBMS's (DDBMs) into three classes. One class consists of blocking CC mechanisms and two classes contain nonblocking CC mechanisms. We define CC overhead and derive it for conflicting and nonconflicting transactions for each class of CC mechanisms. Since CC overhead is dependent on CC mechanism only, it can be used as a metric for comparison of CC mechanisms and as a measure of CC load on DDBMS resources. We also describe two new nonblocking distributed concurrency control mechanisms which use the concept of multiple data object versions. One is based on time stamp ordering of transaction execution and the other is based on nonserializable execution detection and recovery to serializable execution. We compare both with distributed two-phase locking; supported by the Foundation Research Program of the Naval Postgraduate School with funds provided by the Chief of Naval Research.; http://archive.org/details/concurrencycontr00bada; NA

Concurrency and synchronization in the INTEL iAPX-432 prototype systems implementation language

MacLennan, Bruce J.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Relatório Formato: 27 p. ; 28 cm.
EN_US
Relevância na Pesquisa
37.06%
This report describes the concurrent execution and synchronization facilities of a prototype systems implementation language for Intel's iAPX-432 microprocessor. Full exploitation of the 432's facilities places many demands on a language intended for systems implementation. This report describes the prototype languages support for the 432's dynamic, message-based model of concurrency. (Author); supported in part by the Foundation Research Program of the Naval Postgraduate School with funds provided by the Chief of Naval Research.; http://archive.org/details/concurrencysynch00macl; Chief of Naval Research; NA

Performance Models of Concurrency Control Protocols for Transaction Processing Systems

Di Sanzo, Pierangelo
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
EN
Relevância na Pesquisa
37.41%
Transaction processing plays a key role in a lot of IT infrastructures. It is widely used in a variety of contexts, spanning from database management systems to concurrent programming tools. Transaction processing systems leverage on concurrency control protocols, which allow them to concurrently process transactions preserving essential properties, as isolation and atomicity. Performance is a critical aspect of transaction processing systems, and it is unavoidably affected by the concurrency control. For this reason, methods and techniques to assess and predict the performance of concurrency control protocols are of interest for many IT players, including application designers, developers and system administrators. The analysis and the proper understanding of the impact on the system performance of these protocols require quantitative approaches. Analytical modeling is a practical approach for building cost-effective computer system performance models, enabling us to quantitatively describe the complex dynamics characterizing these systems. In this dissertation we present analytical performance models of concurrency control protocols. We deal with both traditional transaction processing systems, such as database management systems...

Generation of Concurrency Controls using Discrete-Event Systems

Dragert, Christopher
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 1893011 bytes; application/pdf
EN; EN
Relevância na Pesquisa
37.22%
The development of controls for the execution of concurrent code is non-trivial. This work shows how existing discrete-event system (DES) theory can be successfully applied to this problem. From code without concurrency controls and a specification of desired behaviours, a DES representation of the problem is obtained, and then used to generate concurrency control code. By applying rigorously proven DES theory, the resulting code comes with guarantees not present in similar works. All control schemes generated in DES are nonblocking, yielding code that is free of both livelock and deadlock. Additionally, the generated control scheme is minimally restrictive, meaning only problematic behaviours are prevented. If the specifications cannot be enforced as presented, the largest controllable subset is instead enforced. The result, which requires no further interaction to generate, is the best possible control scheme given the interaction between the specifications and the original code. Existing methods encounter difficulties when faced with multiple specifications that interact to form deadlocks. Modular DES theory is successfully applied, allowing resolution of these conflicts without requiring the user to introduce new specifications. Moreover...

Using Discrete-Event Systems for the Automatic Generation of Concurrency Control for Dynamic Threads

Auer, Anthony
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
37.06%
The application of Discrete-Event Systems (DES) theory to the problem of guar- anteeably enforcing concurrency constraints in multi-threaded applications has been studied under certain assumptions, namely, the assumption of a static pool of pre- existing instantiated threads, whose creation and termination are not modelled. This work proposes an extension of this case to handle dynamically instantiated and termi- nated threads using a Petri net formalism and an online limited-lookahead state-space search technique.; Thesis (Master, Computing) -- Queen's University, 2010-05-27 17:00:15.99

“This is the Medicine:” A Kenyan community responds to a sexual concurrency reduction intervention

Knopf, Amelia; Agot, Kawango; Sidle, John; Naanyu, Violet; Morris, Martina
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.47%
We report the results of the first study designed to evaluate the feasibility and acceptability of an HIV prevention intervention focused on concurrent sexual partnerships. Mathematical models and longitudinal studies of stable couples indicate concurrency plays a critical role in sustaining generalized HIV epidemics in heterosexual populations, and East and Southern African nations identified concurrency reduction as a priority for HIV prevention. "Know Your Network" (KYN) is a single-session community-level concurrency awareness intervention designed to address this need. It is rooted in traditional social network research, but takes advantage of new network methodology and years of participatory action research with communities living in a region of Kenya with the highest HIV prevalence nationally. KYN combines didactic presentation, interactive exercises, high-impact graphics, and a network survey with immediate visualization of the results, to prompt a community conversation about sexual norms. We combined focus group discussions and the traditional east African baraza to evaluate the feasibility and acceptability of KYN for use with adults living in rural Nyanza Province, Kenya. We were able to implement KYN with fidelity to its components. Participants understood the intervention's messages about concurrency and its role in HIV transmission through sexual networks. They agreed to provide anonymous egocentric data on their sexual partnerships...

Measuring and modelling concurrency

Sawers, Larry
Fonte: International AIDS Society Publicador: International AIDS Society
Tipo: Artigo de Revista Científica
Publicado em 12/02/2013 EN
Relevância na Pesquisa
27.63%
This article explores three critical topics discussed in the recent debate over concurrency (overlapping sexual partnerships): measurement of the prevalence of concurrency, mathematical modelling of concurrency and HIV epidemic dynamics, and measuring the correlation between HIV and concurrency. The focus of the article is the concurrency hypothesis – the proposition that presumed high prevalence of concurrency explains sub-Saharan Africa's exceptionally high HIV prevalence. Recent surveys using improved questionnaire design show reported concurrency ranging from 0.8% to 7.6% in the region. Even after adjusting for plausible levels of reporting errors, appropriately parameterized sexual network models of HIV epidemics do not generate sustainable epidemic trajectories (avoid epidemic extinction) at levels of concurrency found in recent surveys in sub-Saharan Africa. Efforts to support the concurrency hypothesis with a statistical correlation between HIV incidence and concurrency prevalence are not yet successful. Two decades of efforts to find evidence in support of the concurrency hypothesis have failed to build a convincing case.

Optimism for Boosting Concurrency

Gramoli, Vincent; Kuznetsov, Petr; Ravi, Srivatsan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.51%
Modern concurrent programming benefits from a large variety of synchronization techniques. These include conventional pessimistic locking, as well as optimistic techniques based on conditional synchronization primitives or transactional memory. Yet, it is unclear which of these approaches better leverage the concurrency inherent to multi-cores. In this paper, we compare the level of concurrency one can obtain by converting a sequential program into a concurrent one using optimistic or pessimistic techniques. To establish fair comparison of such implementations, we introduce a new correctness criterion for concurrent programs, defined independently of the synchronization techniques they use. We treat a program's concurrency as its ability to accept a concurrent schedule, a metric inspired by the theories of both databases and transactional memory. We show that pessimistic locking can provide strictly higher concurrency than transactions for some applications whereas transactions can provide strictly higher concurrency than pessimistic locks for others. Finally, we show that combining the benefits of the two synchronization techniques can provide strictly more concurrency than any of them individually. We propose a list-based set algorithm that is optimal in the sense that it accepts all correct concurrent schedules. As we show via experimentation...

Rethinking serializable multiversion concurrency control

Faleiro, Jose M.; Abadi, Daniel J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.41%
Multi-versioned database systems have the potential to significantly increase the amount of concurrency in transaction processing because they can avoid read-write conflicts. Unfortunately, the increase in concurrency usually comes at the cost of transaction serializability. If a database user requests full serializability, modern multi-versioned systems significantly constrain read-write concurrency among conflicting transactions and employ expensive synchronization patterns in their design. In main-memory multi-core settings, these additional constraints are so burdensome that multi-versioned systems are often significantly outperformed by single-version systems. We propose Bohm, a new concurrency control protocol for main-memory multi-versioned database systems. Bohm guarantees serializable execution while ensuring that reads never block writes. In addition, Bohm does not require reads to perform any book-keeping whatsoever, thereby avoiding the overhead of tracking reads via contended writes to shared memory. This leads to excellent scalability and performance in multi-core settings. Bohm has all the above characteristics without performing validation based concurrency control. Instead, it is pessimistic, and is therefore not prone to excessive aborts in the presence of contention. An experimental evaluation shows that Bohm performs well in both high contention and low contention settings...

On the Cost of Concurrency in Transactional Memory

Kuznetsov, Petr; Ravi, Srivatsan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.47%
The crux of software transactional memory (STM) is to combine an easy-to-use programming interface with an efficient utilization of the concurrent-computing abilities provided by modern machines. But does this combination come with an inherent cost? We evaluate the cost of concurrency by measuring the amount of expensive synchronization that must be employed in an STM implementation that ensures positive concurrency, i.e., allows for concurrent transaction processing in some executions. We focus on two popular progress conditions that provide positive concurrency: progressiveness and permissiveness. We show that in permissive STMs, providing a very high degree of concurrency, a transaction performs a linear number of expensive synchronization patterns with respect to its read-set size. In contrast, progressive STMs provide a very small degree of concurrency but, as we demonstrate, can be implemented using at most one expensive synchronization pattern per transaction. However, we show that even in progressive STMs, a transaction has to "protect" (e.g., by using locks or strong synchronization primitives) a linear amount of data with respect to its write-set size. Our results suggest that looking for high degrees of concurrency in STM implementations may bring a considerable synchronization cost.

A Concurrency Control Method Based on Commitment Ordering in Mobile Databases

Karami, Ali; Baraani-Dastjerdi, Ahmad
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/12/2011
Relevância na Pesquisa
27.41%
Disconnection of mobile clients from server, in an unclear time and for an unknown duration, due to mobility of mobile clients, is the most important challenges for concurrency control in mobile database with client-server model. Applying pessimistic common classic methods of concurrency control (like 2pl) in mobile database leads to long duration blocking and increasing waiting time of transactions. Because of high rate of aborting transactions, optimistic methods aren`t appropriate in mobile database. In this article, OPCOT concurrency control algorithm is introduced based on optimistic concurrency control method. Reducing communications between mobile client and server, decreasing blocking rate and deadlock of transactions, and increasing concurrency degree are the most important motivation of using optimistic method as the basis method of OPCOT algorithm. To reduce abortion rate of transactions, in execution time of transactions` operators a timestamp is assigned to them. In other to checking commitment ordering property of scheduler, the assigned timestamp is used in server on time of commitment. In this article, serializability of OPCOT algorithm scheduler has been proved by using serializability graph. Results of evaluating simulation show that OPCOT algorithm decreases abortion rate and waiting time of transactions in compare to 2pl and optimistic algorithms.; Comment: 15 pages...

Virtual Machine Support for Many-Core Architectures: Decoupling Abstract from Concrete Concurrency Models

Marr, Stefan; Haupt, Michael; Timbermont, Stijn; Adams, Bram; D'Hondt, Theo; Costanza, Pascal; De Meuter, Wolfgang
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/02/2010
Relevância na Pesquisa
27.51%
The upcoming many-core architectures require software developers to exploit concurrency to utilize available computational power. Today's high-level language virtual machines (VMs), which are a cornerstone of software development, do not provide sufficient abstraction for concurrency concepts. We analyze concrete and abstract concurrency models and identify the challenges they impose for VMs. To provide sufficient concurrency support in VMs, we propose to integrate concurrency operations into VM instruction sets. Since there will always be VMs optimized for special purposes, our goal is to develop a methodology to design instruction sets with concurrency support. Therefore, we also propose a list of trade-offs that have to be investigated to advise the design of such instruction sets. As a first experiment, we implemented one instruction set extension for shared memory and one for non-shared memory concurrency. From our experimental results, we derived a list of requirements for a full-grown experimental environment for further research.

Towards Composable Concurrency Abstractions

Swalens, Janwillem; Marr, Stefan; De Koster, Joeri; Van Cutsem, Tom
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/06/2014
Relevância na Pesquisa
27.61%
In the past decades, many different programming models for managing concurrency in applications have been proposed, such as the actor model, Communicating Sequential Processes, and Software Transactional Memory. The ubiquity of multi-core processors has made harnessing concurrency even more important. We observe that modern languages, such as Scala, Clojure, or F#, provide not one, but multiple concurrency models that help developers manage concurrency. Large end-user applications are rarely built using just a single concurrency model. Programmers need to manage a responsive UI, deal with file or network I/O, asynchronous workflows, and shared resources. Different concurrency models facilitate different requirements. This raises the issue of how these concurrency models interact, and whether they are composable. After all, combining different concurrency models may lead to subtle bugs or inconsistencies. In this paper, we perform an in-depth study of the concurrency abstractions provided by the Clojure language. We study all pairwise combinations of the abstractions, noting which ones compose without issues, and which do not. We make an attempt to abstract from the specifics of Clojure, identifying the general properties of concurrency models that facilitate or hinder composition.; Comment: In Proceedings PLACES 2014...

A comparative study of concurrency control algorithms for distributed databases

Aparicio, Fabio
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
37.33%
The declining cost of computer hardware and the increasing data processing needs of geographically dispersed organizations have led to substantial interest in distributed data management. These characteristics have led to reconsider the design of centralized databases. Distributed databases have appeared as a result of those considerations. A number of advantages result from having duplicate copies of data in a distributed databases. Some of these advantages are: increased data accesibility, more responsive data access, higher reliability, and load sharing. These and other benefits must be balanced against the additional cost and complexity introduced in doing so. This thesis considers the problem of concurrency control of multiple copy databases. Several synchronization techniques are mentioned and a few algorithms for concurrency control are evaluated and compared.