published_or_final_version / abstract / Computer Science / Doctoral / Doctor of Philosophy

[pt] Referências fracas e finalizadores constituem uma alternativa elegante para se obter controle sobre a interação entre a aplicação e o coletor de lixo. No entanto, em alguns contextos, finalizadores são desnecessários, pois é possível estender o mecanismo de referências fracas a fim de dar suporte a finalização. Neste trabalho, realizamos um estudo detalhado sobre os usos desses mecanismos e mostramos como é possível substituir finalizadores por referências fracas propondo uma implementação baseada em referências fraca para cada uso de finalizadores. Baseado nesse estudo, desenvolvemos um mecanismo de finalização via referências fracas para a linguagem Lua. Motivados por nossa proposta de uma maior exploração do mecanismo de referências, desenvolvemos um algoritmo para um importante problema relacionado a ciclos em tabelas fracas, uma estrutura criada a partir de referências fracas. A existência de referências cíclicas entre chaves e valores impede que os elementos que compõem o ciclo sejam coletados, mesmo que eles não sejam mais utilizados pelo programa. Isso acaba dificultando o uso de tabelas fracas em determinadas aplicações. A linguagem Haskell resolveu esse problema através de uma adaptação do mecanismo de ephemerons ao seu coletor de lixo. Partindo desse fato, modificamos a implementação do coletor de lixo de Lua para que este oferecesse suporte ao mecanismo de ephemerons. Dessa forma, pudemos eliminar o problema de ciclos em tabelas fracas nessa linguagem. / [en] Weak References and finalizers constitute an elegant alternative to obtain control over the interaction between the application and the garbage collector. However, in some contexts, finalizers are not necessary because it`s possible to extend the weak reference mechanism in order to give support to finalization. In this work, we present a survey of the most common uses of these mechanisms. We also show how weak references can replace finalizers proposing a weak reference based implementation for each finalizer use. Based on this survey, we developed a finalization mechanism based on weak references for the Lua programming language. Motivated by our proposal of a better exploration of the weak reference mechanism, we developed a solution for an important problem related to cycles on weak tables, an structure created using weak references. Cyclic references between keys and values prevents the elements inside the cycle from being collected, even if they are no more reachable. This ends up bringing difficulties to the use of weak tables in certain kinds of applications. The Haskell programming language solved this problem implementing an adaptation of a mechanism called ephemerons. Based on this fact, we modified the Lua garbage collector in order to offer support to ephemerons. As a result, we were able to solve the problem of cycles on weak tables in Lua.

Submitted by admin tede (tede@pucgoias.edu.br) on 2017-02-23T17:59:12Z No. of bitstreams: 1 ALAIR AMBROSIO DO NASCIMENTO.pdf: 3653783 bytes, checksum: 1a2132f5d48442a9db24cc1325f31750 (MD5) / Made available in DSpace on 2017-02-23T17:59:12Z (GMT). No. of bitstreams: 1 ALAIR AMBROSIO DO NASCIMENTO.pdf: 3653783 bytes, checksum: 1a2132f5d48442a9db24cc1325f31750 (MD5) Previous issue date: 2015-03-26 / The purpose of this dissertation was to investigate the program of selective collection of recyclable materials in Goiânia. The survey also proposed raising if the municipality has a Municipal Program of Integrated Solid Waste Management (PMGIRS). This work investigated the performance of recycling cooperatives of recyclable materials in the following aspects: physical structure of cooperatives, working conditions of the members, the formation of cooperatives in networks, partnerships with municipal government, the documentary and legal aspects, and working conditions of members. The interviews were done with the members of the Goiânia City Hall, so as with representatives of the Municipal Environment Agency (AMMA), Goiania Urbanization Company (COMURG), Members of the Social Incubator recyclable materials from the Goiás Federal University (UFG) and representatives of fourteen recycling cooperatives registered by the city of Goiânia. / A proposta desta dissertação foi investigar o programa da coleta seletiva de materiais recicláveis no município de Goiânia, e levantar se o município conta com o Programa Municipal de Gestão Integrada de Resíduos Sólidos, (PMGIRS). O trabalho pesquisou a atuação das cooperativas de catadores de materiais recicláveis sob os seguintes aspectos: estrutura física das cooperativas, as condições de trabalho dos cooperados, a formação das cooperativas em redes, as parcerias firmadas com poder público municipal, os aspectos documental e legal. A pesquisa utilizada foi de natureza exploratória qualitativa e quantitativa, o universo de atores entrevistados foi composto por membros da Prefeitura Municipal de Goiânia, como representantes da Agencia Municipal do Meio Ambiente (AMMA), e da Companhia de Urbanização de Goiânia (COMURG), Membro da Incubadora Social da Universidade Federal de Goiás (UFG), e representantes das quatorze cooperativas de catadores de materiais recicláveis cadastradas pela Prefeitura Municipal de Goiânia.

Garbage collectors (GCs) automate the problem of deciding when objects are no longer reachable and therefore should be reclaimed, however, there currently exists no automated process for the design of a correct garbage collector. Formal models exist that prove the correctness of individual GCs; more general models describe a wider range of GCs but do not prove their correctness or provide a concrete instantiation process. The lack of a formal model means that GCs have been designed in an ad-hoc manner, published without proof of correctness and with bugs; it also means that it is difficult to apply experience gained from one implementation to the design of another. This thesis presents Surf, an abstract model of distributed garbage collection that bridges the gap between expressibility and specificity: it can describe a wide range of GCs and contains a proof of correctness that defines a list of requirements that must be fulfilled. Surf’s design space and its requirements for correctness provide a process that may be followed to analyse an existing collector or create a new GC. Surf predicts the abstract behaviour of GCs; this thesis evaluates those predictions in light of the understood behaviour of published GCs to confirm the accuracy of the model. A distributed persistent implementation of the Train Algorithm is created as an instantiation of Surf and the model is used to analyse progress in the GC and drive the design of a partition selection policy that provides a lower bound on progress and therefore reduces the GC’s complexity to completeness. Tests with mesh data structures from finite element analysis confirm the progress predictions from Surf. Published GCs cluster mostly in one corner of the Surf design space so this thesis explores the design of a GC at an unoccupied design point: the Tram Algorithm. Analysis via Surf leads to the prediction that Trams are capable of discovering topology in the live object graph that approximately identifies the strongly connected components, permitting O(1) timeliness that is unique to the Tram Algorithm. / Thesis (Ph.D.) -- University of Adelaide, School of Computer Science, 2008

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

<p>This report evaluates whether an interpreted high-level garbage collected language has enough information about its memory behaviour to make better cache decisions than modern general CPU hardware.</p><p>With a generational garbage collector, depending on promotion algorithm and generation size, around 90% of all objects never leave the first generation. This report is based on the hypothesis that, because of the low promotion rate, accesses to higher generations are sufficiently rare not to benefit from caching.</p><p>To test this hypothesis, we built an operating system with a Scheme interpreter in kernel mode, where the interpreter controls the cache. Generic x86 PC hardware was used, since it allows fine-grained control of cache decisions.</p><p>Measurements of execution time in this interpreter show that disabling the cache for generations higher than the first does not give any performance gain, but rather a performance loss of up to 50%.</p><p>We conclude that this interpreter design is not an improvement, but cannot conclude that the hypothesis is false in general. We suggest building a better CPU simulator to gather more data from which to make better caching decisions, moving internal interpreter data structures into the garbage collected heap and modifying the hardware to allow control in the currently rigid dimension of where data is cached---for example separate control of instruction and data caches and separate data caches for different areas of memory.</p>

Thesis (Ph. D.)--University of Hong Kong, 2006. / Also available online.

This report details the design of a garbage collection (GC) module, which introduces modern GC features to the domain of embedded implementations. The described design supports weak references and feeds reference queues. Its architecture allows multiple concurrent application cores operating as mutators on the shared memory managed by the GC module. The garbage collection is exact and fully concurrent so as to enable the uninterrupted computational progress of the mutators. It combines a distributed root marking with a centralized heap scan of the managed memory. It features a novel mark-and-copy GC strategy on a segmented memory, which thereby overcomes both the tremendous space overhead of two-space copying and the compaction race of mark-and-compact approaches. The proposed GC architecture has been practically implemented and proven using the embedded bytecode processor SHAP as a sample testbed. The synthesis results for settings up to three SHAP mutator cores are given and online functional measurements are presented. Basic performance dependencies on the system configuration are evaluated.

Thesis (M.A.)--Miami University, Dept. of Geography, 2005. / Title from first page of PDF document. Document formatted into pages; contains [1], v, 53 p. : ill. Includes bibliographical references (p. 50-53).

O objetivo desta dissertação foi mostrar o cenário atual e as perspectivas para o setor de saneamento básico do Estado de Roraima. Destacou-se o perfil dos serviços de abastecimento de água, coleta de esgotos e coleta de lixo. Foram utilizadas diversas publicações, especialmente as do Instituto Brasileiro de Geografia e Estatística/IBGE, com destaque para a Pesquisa Nacional por Amostra de Domicílios/PNAD e o Censo Demográfico 2000, que forneceram dados da população urbana do Estado atendida e não atendida pelos serviços de saneamento básico. Dessa forma, foi realizada a comparação dos resultados obtidos para o Estado com algumas cidades brasileiras, regiões do país, além de outros países. Sob esse aspecto, os resultados apurados apontaram que 96,9% dos domicílios urbanos do Estado, são atendidos pelos serviços de abastecimento de água, superando a realidade nacional. Quanto à coleta de esgotos, os resultados são preocupantes, uma vez que apenas 17,3% dos domicílios urbanos do Estado são atendidos por este serviço. Já a coleta de lixo 97,1% dos domicílios urbanos do Estado possui acesso a esse serviço. Constatou-se, ainda, que a maior parte do lixo coletado no Estado de Roraima é depositada a céu aberto, sem nenhum tratamento quanto às questões ambientais. Concluiu-se que a população urbana do Estado de Roraima apresenta ótimos resultados quanto ao acesso aos serviços de abastecimento de água e coleta de lixo. Contudo, a mesma situação não é observada quanto ao acesso aos serviços de coleta de esgotos, onde uma pequena parcela da população urbana é atendida. Nesse sentido, já existem recursos disponíveis para a universalização dos serviços de abastecimento de água e ampliação do sistema de esgoto sanitário. Entretanto, os recursos destinados a ampliação do sistema de esgotos ainda não é suficiente para atender a toda a população. / The objective of this thesis was to show the current scenario and prospects for the basic sanitation sector in the State of Roraima, showing the profile of the following services: water supply, waste sewage disposal and garbage collection. To obtain the data, various publications were used , especially the Brazilian Institute of Geography and Statistics (IBGE), highlighting the National Survey of Home Sampling (PNAD) and the year 2000 Census which provided data on the urban population of the state with and without sanitation services. Thus, the results for the state were compared with other Brazilian cities, regions of the country and other countries. The findings indicate that 96.9% of urban households in the state are served by the water supply, surpassing the national reality, while the sewage disposal results are worrisome as only 17.3% of urban households in the state are served. As for garbage collection, 97.1% of urban households of the state have access to this service. It was further observed that most of the garbage collected in the state of Roraima is deposited in the open, without any form of treatment for environmental concerns. It was concluded that the urban population of the state of Roraima in great part have access to services of water supply and garbage collection. However, the same was not observed for sewage disposal services, where only a small portion of the urban population is served. There are resources available for expanding the water supply to service more households and the expansion of the sewerage system. However, the resources allocated for the expansion of sewerage system is not sufficient to meet the demands of the entire state population, and so, the need for a larger volume of investment.