Garbage Collection

Safepoints are a virtual machine mechanism that allows one thread to suspend other threads in a known state so that runtime actions can be performed without interruption and with data structures in a consistent state. Many virtual machines use safepoints as a mechanism to provide services such as stop-the-world garbage collection, debugging, and modification to running code such as installing or replacing classes. Languages implemented on these virtual machines may have access to these services, but not directly to the safepoint mechanism itself. We show that safepoints have many useful applications for the implementation of guest languages running on a virtual machine. We describe an API for using safepoints in languages that were implemented under the Truffle language implementation framework on the Java Virtual Machine and show several applications of the API to implement useful guest-language functionality. We present an efficient implementation of this API, when running in combination with the Graal dynamic compiler. We also demonstrate that our safepoints cause zero overhead with respect to peak performance and statistically insignificant overhead with respect to compilation time. We compare this to other techniques that could be used to implement the same functionality and demonstrate the large overhead that they incur.

Object colocation is an optimization that reduces memory access costs by grouping together heap objects so that their order in memory matches their access order in the program. We implemented this optimization for Sun Microsystems' Java HotSpot TM VM. The garbage collector, which moves objects during collection, assigns consecutive addresses to connected objects and handles them as atomic units. We use read barriers inserted by the just-in-time compiler to detect the most frequently accessed fields per class. These "hot fields" are added to so-called hot-field tables, which are then used by the garbage collector for colocation decisions. Read barriers that are no longer needed are removed in order to reduce the overhead. Our analysis is performed automatically at run time and requires no actions on the side of the programmer. We measured the impact of object colocation on the young and the old generation of the garbage collector, as well as the difference between dynamic colocation using read barriers and a static colocation strategy where colocation decisions are done at compile time. Our measurements show that object colocation works best for the young generation using a read-barrier-based approach.

Array inlining expands the concepts of object inlining to arrays. Groups of objects and arrays that reference each other are placed consecutively in memory so that their relative offsets are fixed, i.e. they are colocated. This allows memory loads to be replaced by address arithmetic, which reduces the costs of field and array accesses. We implemented this optimization for Sun Microsystems' Java HotSpot TM VM. The optimization is performed automatically and requires no actions on the part of the programmer. Arrays are frequently used for the implementation of dynamic data structures. Therefore, the length of arrays often varies, and fields referencing such arrays have to be changed whenever the array is reallocated. We present an efficient code pattern that detects these changes and allows the optimized access of such array fields. It is integrated into the array bounds check. We also claim that inlining array element objects into an array is not possible without a global data flow analysis. The evaluation shows that our dynamic approach can optimize frequently accessed fields with a reasonable low compilation and analysis overhead. The peak performance of SPECjvm98 is improved by 10% on average, with a maximum of 25%.

Dynamic code evolution is a technique to update a program while it is running. In an object-oriented language such as Java, this can be seen as replacing a set of classes by new versions. We modified an existing high-performance virtual machine to allow arbitrary changes to the definition of loaded classes. Besides adding and deleting fields and methods, we also allow any kind of changes to the class and interface hierarchy. Our approach focuses on increasing developer productivity during debugging. Changes can be applied at any point a Java program can be suspended. The evaluation section shows that our modifications to the virtual machine have no negative performance impact on normal program execution. The fast in-place instance update algorithm ensures that the performance characteristics of a change are comparable with performing a full garbage collection run. Standard Java development environments are capable of using the code evolution features of our modified virtual machine, so no additional tools are required.

Smart Cities' Systems are the main elements as systematic for the development of smart cities in targeting the most updating system ever. Now adays, many countries around the world have been spared and no effort in indorsing smart cities and not yet clearly appreciated. Smart Cities' System is an interesting technological advancement that can make people's lives much more convenient, comfortable and suitable. The progress of smart cities includes loT of technological aspects, which contains big data, mobile networks, cloud computing, Internet of Things, and even artificial intelligence as well. Digital information is the basic and main component of signal control and flow in any smart city. Therefore, information security is another significant aspect. In the incident of equipment catastrophe, the task of safeguarding the system's information is of the utmost standing. Since smart cities are automatically measured, the problematic of mobile network security must be taken into consideration. To take these issues into consideration, this study focuses on information security, big data, mobile networks, cloud computing, and the Internet of Things to investigate the important of Smart Cities Systems. Security efficiency can be enhanced by using a Secure Hash Algorithm 256 (SHA-256), which is an authentication mechanism that, with the help of the user, can authenticate each interaction of a given device with a Web Server by using an encrypted username, password, etc.

The traditional waste management technique often results in inadequate and ecologically harmful activities in urban settings, similar to daily mail deliveries to an empty mailbox. Regardless matter whether trash cans are full or practically empty, garbage trucks keep to a set schedule, using extra fuel, blocking up traffic, and generating more carbon emissions. This project offers an innovative technique: a Smart Waste Management System that makes use of machine learning and IoT (Internet of Things) software. Garbage cans have specialized sensors installed that allow for real-time fill level detection. An automated signal is sent to the garbage truck for pickup when a bin fills to a predefined level. The automated system reduces fuel consumption and the carbon footprint of garbage disposal by managing waste collection routes. This technique not only conserves resources but also improves sustainability in urban areas by making a comparison to mail delivery, which only happens when there is mail to distribute. An easy-to-use mobile app that alerts users when trash cans need maintenance and garbage trucks are approaching gives residents leverage. In addition to providing a workable answer to a critical urban problem, this project advances the management of waste in cities in the direction of a greener and more effective future

We present a bottom-up copying garbage collector for WAM based Prolog. In contrast to the top-down copying garbage collector of Bevemyr and Lindgren, it preserves the order of the heap segments in the WAM like sliding collectors do, so that space can be reclaimed on backtracking, Moreover, the collector can move some old data to newer segments so that future instant redahuing becomes better than with sllding collectors; this behavior can not be explained by use)Culhess logic and applies when the underlying Prolog machine implements ehoieepoint trimming. The algorithm is mostly explained informally through examples. The garbage collector is implemented in the context of Bin-Prolog, a production quality Prolog system working on various 32-bit and 64-bit architectures. It shows outstanding practiced performance when compared with the high-quality sliding collector of SICStus Prolog. Recently, [4] described a top-down copying collector (whose details are recidled in section 2) which has the drawback

Multiversioning is widely used in databases, transactional memory, and concurrent data structures. It can be used to support read-only transactions that appear atomic in the presence of concurrent update operations. Any system that maintains multiple versions of each object needs a way of efficiently reclaiming them. We experimentally compare various existing reclamation techniques by applying them to a multiversion tree and a multiversion hash table. Using insights from these experiments, we develop two new multiversion garbage collection (MVGC) techniques. These techniques use two novel concurrent version list data structures. Our experimental evaluation shows that our fastest technique is competitive with the fastest existing MVGC techniques, while using significantly less space on some workloads. Our new techniques provide strong theoretical bounds, especially on space usage. These bounds ensure that the schemes have consistent performance, avoiding the very high worst-case space usage of other techniques. CCS Concepts: • Computing methodologies Ñ Concurrent algorithms.

Despite the fact that Solid State Disk (SSD) data storage media had offered a revolutionary property storages community, but the unavailability of a comprehensive allocation strategy in SSDs storage media, leads to consuming the available space, random writing processes, time-consuming reading processes, and system resources consumption. In order to overcome these challenges, an efficient allocation algorithm is a desirable option. In this paper, we had executed an intensive investigation on the SSD-based allocation algorithms that had been proposed by the knowledge community. An explanatory comparison had been made between these algorithms. We reviewed these algorithms in order to building advanced knowledge armature that would help in inventing new allocation algorithms for this type of storage media.

I. PROBLEMATIQUE DE LA RECHERCHE p.3 A. La grande vine africaine, la mal-aimee p. 4 De l'incarnation du mal-developpement a celle de la crise p. 6 La presomption d'echec des politiques publiques urbaines p. 8 L'inconnue pendante du gouvernement des villes p. 13 B. Au-dela de la confusion : eclairer « l'Etat au concret » par l'analyse de l'action publique urbaine p. 16 Sociologisation de l'analyse de l'action publique p. 18 L'action publique urbaine privilegiee p. 20 Une sociologie necessairement politique de l'action publique p. 22 L'analyse de « l'Etat au concret » et de ses modes de reinvention p. 26 Une reflexion déjà ouverte p. 29 II. OBJET, TERRAIN DE LA RECHERCHE ET METHODOLOGIE p.35 Le renouvellement des modalites de regulation urbaine au travers de l'analyse de la carriere d'un probleme public (1964-2002) p. 35 Nairobi, Self-Help City (la ville de la debrouille) p. La politique publique de gestion des dechets p. III. HYPOTHESES DE TRAVAIL ET LEUR ARTICULATION p.43 Hypotheses de travail p. 43 Presentation de l'analyse p.

A Universidade do Estado de Mato Grosso (UNEMAT) possui 13 campi distribuidos em todo o estado, tendo como principal missao a de levar o ensino publico de qualidade, o conhecimento cientifico e tecnologico para o interior de Mato Grosso. A UNEMAT incentiva a formacao de profissionais conscientes de sua responsabilidade social por meio da extensao universitaria sob enfoque da relacao entre Estado e Sociedade contribuindo para o desenvolvimento da comunidade local, regional e nacional.

Automatic Design of Trash Cans in the Arduino Uno R3 System is designed for waste management which is often a problem in many cities. Waste management is currently one of the factors that always influences the creation of a clean and healthy environment. Garbage that is always left alone over time will accumulate and pile up so that no one takes care of it, irregular waste is a problem that often occurs. In the waste collection process, which will be carried out by checking the garbage collection sites one by one, the work will be ineffective and inefficient, because it will take a lot of wasted time, even time and money. Furthermore, to simplify the waste disposal process, this can be done at any time, because the process is very easy and can be done or done by anyone. The result is that the ultrasonic sensor is used to capture objects or objects in front of it, then there is a servo motor that can move when someone throws trash, after that there is an LCD display that will display...

Implementing a concurrent programming language such as Java by means of a translator to an existing language is attractive as it provides portability over all platforms supported by the host language and reduces development time—as many low‐level tasks can be delegated to the host compiler. The C and C++ programming languages are popular choices for many language implementations due to the availability of efficient compilers on a wide range of platforms. For garbage‐collected languages, however, they are not a perfect match as no support is provided for accurately discovering pointers to heap‐allocated data on thread stacks. We evaluate several previously published techniques and propose a new mechanism, lazy pointer stacks, for performing accurate garbage collection in such uncooperative environments. We implemented the new technique in the Ovm Java virtual machine with our own Java‐to‐C/C++ compiler using GCC as a back‐end compiler. Our extensive experimental results confirm that ...

Bank sampah adalah sebuah sistem pengelolaan sampah berbasis masyarakat yang bertujuan untuk mengurangi jumlah sampah yang berakhir di tempat pembuangan akhir (TPA) dan meningkatkan kesadaran lingkungan. Dalam sistem ini, masyarakat dapat menukarkan sampah yang telah dipilah, seperti sampah plastik, kertas, dan logam, untuk mendapatkan insentif berupa uang atau poin yang dapat digunakan untuk berbagai keperluan. Bank sampah berperan penting dalam mendukung konsep ekonomi sirkular dengan cara mengubah sampah menjadi sumber daya yang bernilai. Selain itu, bank sampah juga membantu mengurangi polusi, memperpanjang umur TPA, dan memberdayakan masyarakat melalui edukasi dan peluang ekonomi. Dengan semakin meningkatnya jumlah bank sampah di berbagai daerah, model ini menunjukkan efektivitasnya sebagai solusi kreatif dalam pengelolaan sampah yang berkelanjutan, sekaligus mendukung upaya pelestarian lingkungan dan kesejahteraan komunitas lokal.

Systems integrating heterogeneous processors with unified memory provide seamless integration among these processors with minimal development complexity. These systems integrate accelerators such as GPUs on the same die with CPU cores to accommodate running parallel applications with varying levels of parallelism. Such integration is becoming very common on modern chip architectures, and it places a burden (or opportunity) on application and system programmers to utilize the full potential of such integrated chips. In this paper we evaluate whether we can obtain any performance benefits from running garbage collection on integrated GPU systems, and discuss how difficult it would be to realize these gains for the programmer. Proliferation of garbage-collected languages running on a variety of platforms from handheld mobile devices to data centers makes garbage collection an interesting target to examine on such platforms and can offer valuable lessons for other applications. We prese...

The growing gap between processor and memory speeds is motivating the need for optimization strategies that improve data locality. A major challenge is to devise techniques suitable for pointer-intensive applications. This paper presents two techniques aimed at improving the memory behavior of pointer-intensive applications with dynamic memory allocation, such as those written in Java. First, we present an allocation time object placement technique based on the recently introduced notion of prolific (frequently instantiated) types. We attempt to co-locate, at allocation time, objects of prolific types that are connected via object references. Then, we present a novel locality based graph traversal technique. The benefits of this technique, when applied to garbage collection (GC), are twofold: (i) it improves the performance of GC due to better locality during a heap traversal and (ii) it restructures surviving objects in a way that enhances locality. On multiprocessors, this techniq...

The empowerment of homemakers has a significant effect on the Implementation of Extermination Transport Collection in handling solid waste to improve the cleanliness of the residential environment. The problem in this study is the low Implementation of 3P, where garbage collection is not left correctly scattered; the Transportation of garbage is not routine every day so that the garbage is scattered. Garbage is not destroyed as often as possible so that it harms health. This study aims to assess the feasibility of implementing 3P in dealing with solid waste by empowering homemakers in Drien Rampak Village, Johan Pahlawan District, West Aceh Regency. This research is a sectional observational study with one group pretest post-test design. I conducted in October 2020, which became the population of housewives with a total sample of 45 people. The study results show differences before and after measuring the 3P Implementation with the empowerment of homemakers in improving the cleanlin...

In the realm of e-commerce, efficient data storage and retrieval mechanisms are imperative for
ensuring seamless user experiences and robust backend operations. This paper explores advanced
data storage techniques tailored to the unique demands of e-commerce, ranging from Solid-State
Drives (SSDs) to Distributed File Systems (DFS). Through a comprehensive review of existing
literature and case studies, this study elucidates the capabilities, advantages, and challenges
associated with each storage solution. By examining the evolving landscape of data storage
technologies, this paper offers insights into the optimal selection and implementation of storage
solutions to enhance the performance, scalability, and reliability of e-commerce platforms.

Garbage accumulation certainly has a negative impact on the surrounding environment so that an adequate waste management system is needed. Poor waste management will cause disease, flooding and reduce environmental beauty. In addition to polluting the environment, garbage can also pollute the soil if it is burned and make the soil unhealthy. The smoke from burning garbage will also cause respiratory problems for the surrounding community. Before transporting the waste to the Final Disposal Site (TPA), the garbage is first collected by means of collection, such as garbage carts that pick up trash from houses to Temporary Disposal Sites (TPS) . At this time, the need for TPS and waste transportation equipment in Kertapati Village, is still experiencing many problems. The small number of TPS makes people litter. Garbage that has been wrapped in plastic is thrown away along the median of the Kertapati Village Palembang road. The garbage that is in the median of the road will be taken by...

School of Computrer Scienice n L-T cr p;'v(artiegie Mellon ('niversitv yP ittsburgh. PA 1521:1 3)S ubmitted for publication. This paper is also p~ublished as Fox XMemorandum(M-SF-93-07. A paper containing some of the results presented in this paper wvill appear in 21st .1nnuial

for their contributions to the implementation of JaphaVM. It was great belonging to this team. I owe a great debt to Pedro Garcez Monteiro, for his valuable contributions to JaphaVM, first at the LIS lab, and later as an HP colleague. Diego Rahn Medaglia and Marcelo S. Neves made important contributions to adapt the OO7 benchmark, create testing environments, and discuss experimental results. You guys are awesome. Haris Volos and Susan Spence, from HP Labs, and Prof. Avelino Zorzo, from PUCRS, reviewed early drafts of this text and made many valuable suggestions. Dejan S. Milojicic, also from HP Labs, provided support and guidance in many ways. I am truly grateful for all their contributions. I would also like to thank collectively all the pioneer researchers of orthogonal persistence, for seeing further into the future. None of this would have been possible without my family: my wife Ana Paula da Fonseca, my daughter Valentina Velez and my mother-in-law Ana Maria Beati. They kept me sane and fed and warm and loved. I dearly love you all. Since I was too young to remember, my mother, Neusa Marisa Elias Dreckmann, fanned the fires of my curiosity and taught me by example how to have the drive and resilience to turn visions into reality. I wouldn't be here if not for her, in many ways.

Despite its widespread use in consumer devices and enterprise storage systems, NAND flash faces a growing number of challenges. While technology advances have helped to increase the storage density and reduce costs, they have also led to reduced endurance and larger block variations, which cannot be compensated solely by stronger ECC or read-retry schemes but have to be addressed holistically. Our goal is to enable low-cost NAND flash in enterprise storage for cost efficiency. We present novel flash-management approaches that reduce write amplification, achieve better wear leveling, and enhance endurance without sacrificing performance. We introduce block calibration, a technique to determine optimal read-threshold voltage levels that minimize error rates, and novel garbage-collection as well as data-placement schemes that alleviate the effects of block health variability and show how these techniques complement one another and thereby achieve enterprise storage requirements. By com...

Diarrhea is one of the main causes of illness and even death associated with waste management. This study aims to analyze the relationship of waste management with the incidence of diarrhea in the slums of District Lima Puluh of Pekanbaru City. Survey method was conducted through observation and distribution of questionnaires on 326 respondents related to education, length of stay, income, knowledge and practice of garbage collection. The data obtained was analized by logistic regression. The results of the study found that 33 outbreaks of diarrhea from 326 bigger respondents occurred in the low level of garbage collection of respondents. Characteristics of length of stay, knowledge and practice of garbage collection have a mutual influence on the occurrence of diarrhea with an influence contribution of 33.9%. Partially, only garbage collection practices have a significant effect on the occurrence of diarrhea (p <0.05; OR = 66.695) which means that respondents with poor waste collection practices have a 66.695 times chance of getting diarrhea compared to respondents with garbage collection practices good. Municipal Government of Pekanbaru City is very important to pay attention to this aspect and improve the service of garbage transportation to realize better settlement society to be able to avoid the occurrence of diarrhea incidence.

This paper presents a new Java oriented monitoring infrastructure that enables tools to observe, analyze and manipulate the execution of distributed Java applications independent of implementation details like instrumentation of monitored entities, hardware platform and application libraries. Tools can access the monitored application via a standardized interface defined by an On-Line Monitoring Interface Specification (OMIS) and extended by a set of new Java-specific services relating to garbage collection, class loading, remote method invocation, etc. The new monitoring functionality can be applied for building various kinds of tools and for adapting the already existing ones, such as performance analyzers, debuggers, etc., working in the on-line mode.

Large object-oriented applications may occupy hundreds of megabytes or even gigabytes of memory. During program execution, a large graph of objects is created and constantly changed. Most object runtimes support some kind of automatic memory management based on garbage collectors (GC) whose idea is the automatic destruction of unreferenced objects. However, there are referenced objects which are not used for a long period of time or that are used just once. These are not garbage-collected because they are still reachable and might be used in the future. Due to these unused objects, applications use much more resources than they actually need. In this paper we present the challenges and possible approaches towards an unused object manager for Pharo. The goal is to use less memory by swapping out the unused objects to secondary memory and only leaving in primary memory only those objects which are needed and used. When one of the unused objects is needed, it is brought back into primary memory.

This is to certify that the research work described in this thesis is the original work of the author and has been carried out under my direct supervision. I have personally gone through all the data/results/materials reported in the manuscript and certify their correctness/authenticity. I further certify that the material included in this thesis is not plagiarized and has not been used in part or full in a manuscript already submitted or in the process of submission in partial/complete fulfillment of the award of any other degree from any institution. I also certify that the thesis has been prepared under my supervision according to the prescribed format and I endorse its evaluation for the award of Bachelor of Science in Electrical Engineering degree through the official procedures of the Institute.

The large number of sociopreneurship in Indonesia is still felt to be insufficient to fulfill government programs. Nara Synergy is here to be part of sociopreneurship in Indonesia. This study uses a qualitative research method, which is based on the philosophy of postpositivism. The study in this study discusses several research sub focuses including 1) the main factors of sociopreneurship, 2) sociopreneurship stakeholders, and 3) the effectiveness of sociopreneurship. The results of the research show that the Berkah Usaha Bersama (BUB) Garbage Bank has been running effectively as in line with the purpose of establishing the Garbage Bank.

In human life, garbage becomes a phenomenon that will always exist as long as humans live and move, therefore garbage needs to be handled seriously and intersively. Garbage in people's lives can have negative and positive consequences, where the positive impact is that it can become manure, as a livelihood for scavengers, as well as as one of the elements in the manufacture of energy, or fuel. While the negative impact is that garbage can cause the spread of disease, as well as ecological damage, the number of floods due to garbage accumulation in rivers close to the population and others. Garbage can be managed by involving all parties, such as the community, government, and other institutions. Garbage can also be reduced in people's lives by composting, replacing burning, reusing, recycling.

With the development of parallel computing, distributed computing, grid computing, a new computing model appeared. The concept of computing comes from grid, public computing and SaaS. The vision of cloud computing is to reduce the cost of ...

This paper explores the methods, tools, and best practices involved in Java Virtual Machine (JVM) dump analysis, specifically focusing on thread, heap, and core dumps. The goal is to provide a comprehensive understanding of how these dumps can be utilized to diagnose performance issues, memory leaks, and application
failures in Java applications.

O objetivo principal do trabalho é o de mostrar como o desafio da sustentabilidade não tem como ser enfrentado a partir de uma perspectiva teórica que desconsidera as dimensões culturais e éticas no processo de tomada de decisão o qual, por sua vez, será supra-individual. Sua estrutura analítica é composta de uma seção onde se discute a capacidade de intervenção humana na natureza e a noção de limites. Outra seção apresenta uma análise das duas principais correntes teóricas em economia sobre a questão ambiental. Em seguida se discute as dificuldades de mudança em função da contradição existente entre padrão de consumo e padrão de acumulação. O trabalho termina com uma análise do processo de tomada de decisão sob incerteza, que inclui uma apresentação do Princípio da Precaução e de uma proposta metodológica de classificação e hierarquização dos problemas ambientais (ciência pós-normal).

In the present day scenario, many times we see that the Garbage bins or Dust bins placed at public places in the cities are overflowing due to increase in the waste every day. It creates unhygienic condition for the people and bad odour around the surroundings this leads in spreading some deadly diseases and human illness; to avoid such a situation we are planning to design Garbage Monitoring System using IoT. In this proposed system there are multiple dustbins located throughout the city or Campus, these dustbins are provided with low cost device which helps in tracking the level of garbage bins and an unique ID will be provided for every dustbin so that it is easy to identify which garbage bin is full. When the level reaches threshold limit, the device will transmit the level along with the unique ID provided. These details can be accessed by the concern authorities from their place with the help of Internet and an immediate action can be made to clean the dustbins.

Sheer increase in volume of data over the last decade has triggered research in cluster computing frameworks that enable web enterprises to extract big insights from big data. While Apache Spark is gaining popularity for exhibiting superior scale-out performance on the commodity machines, the impact of data volume on the performance of Spark based data analytics in scale-up configuration is not well understood. We present a deep-dive analysis of Spark based applications on a large scale-up server machine. Our analysis reveals that Spark based data analytics are DRAM bound and do not benefit by using more than 12 cores for an executor. By enlarging input data size, application performance degrades significantly due to substantial increase in wait time during I/O operations and garbage collection, despite 10% better instruction retirement rate (due to lower L1 cache misses and higher core utilization). We match memory behaviour with the garbage collector to improve performance of applications between 1.6x to 3x.

In this paper, we describe an efficie nt and flexible generation scavenging garbage collector toolkit. Our methodology exceeds in systems where the cost associated with any single operation is bounded by small time constant. The collector maintains several "generations" of objects. Newly created objects are all put in the "youngest generation" and when the space allocated for that generation is full, the collector will use the root set to reclaim dead objects from the youngest generation only, leaving the older generations untouched. Objects that survive after several collections of the youngest generation are "promoted" to the older generation. In this way the collector assures that recently created regions will contain high percentages of garbage and will be garbage collected frequently. The framework has been implemented in a library and tested against formidable real world applications. Hence the proposed system eliminates the possibility of storagemanagement bugs and making the design of complex, object-oriented systems much easier. This can be accomplished with almost no change to the language itself and only small changes to existing implementations, while retaining compatibility with existing class libraries.

Half the world's population is expected to live in urban areas by 2020. The high human density and changes in peoples' consumption habits result in an everincreasing amount of trash that must be handled by governing bodies. Problems created by inefficient or dysfunctional cleaning services are exacerbated by a poor personal trash management culture. In this paper we present Cleanly, an urban trashducation system aimed at creating awareness of garbage production and management, which may serve as an educational platform in the urban environment. We report on data collected from an online survey, which not only motivates our research but also provides useful information on reasons and possible solutions for trash problems.

I would not have been able to provide and complete this Thesis without the sincere support and help of many people. Foremost, I would like to thank my supervisor Dr. Steve Counsell for his patience, motivation, advice, and continuous help and support. He made my PhD journey an excellent experience with his knowledge, kindness, thoughtfulness and encouragement. I would like to dedicate my deep thanks for my mother, for the encouragement she provided, her unlimited patience, prayers and the sacrifices she made to help me after my father passed away, which without, I would not be able to achieve my goals and survive difficult times. I am greatly indebted to my sincere wife Dalia and my daughter Julie, without their hopeful smiles, emotional support, patience, understanding and infinite love I would not have been able to stand during the difficult moments in my PhD. I would like to convey my sincerest gratitude to my uncle Wahid Hamza who has been supportive through all my life stages. His sympathy and understanding were enormous and significantly appreciated. I am very grateful to all people in the Department of Information Systems and Computing at Brunel University who helped me during my study and provided such a friendly and comfortable environment. Last, but by no means least, I would like to thank all my friends and colleagues who have been my other family in the UK.

Eq hash tables, which support arbitrary objects as keys, distinguish keys via pointer comparison and often employ hash functions that utilize the address of the object. When compacting garbage collectors move garbage collected objects, the addresses of such objects may change, thus invalidating the hash function computation. A common solution is to rehash all of the entries in an eq hash table on the first access to the table after a collection. For a simple stop-and-copy garbage collector, which moves every element of a hash table, the rehashing overhead is proportional to the amount of work done by the collector and so the cost of rehashing adds only constant overhead. Generational copying collectors, however, may move a few or none of the entries, so rehashing a large table may cost considerably more than the garbage collection run that caused the rehash. In other words, such rehashing is not "generation friendly." In this paper, we describe an efficient, generation-friendly mechanism for implementing eq hash tables. The amount of work required for rehashing is proportional to the work performed by the collector as only objects that actually move during a collection are rehashed. The collector supports eq hash tables and their variants via a simple new type of object, a transport link cell, the handling of which by the collector is nearly trivial.

Eq hash tables, which support arbitrary objects as keys, distinguish keys via pointer comparison and often employ hash functions that utilize the address of the object. When compacting garbage collec- tors move garbage collected objects, the addresses of such objects may change, thus invalidating the hash function computation. A common solution is to rehash all of the entries in an eq hash ta- ble on the first access to the table after a collection. For a simple stop-and-copy garbage collector, which moves every element of a hash table, the rehashing overhead is proportional to the amount of work done by the collector and so the cost of rehashing adds only constant overhead. Generational copying collectors, however, may move a few or none of the entries, so rehashing a large table may cost considerably more than the garbage collection run that caused the rehash. In other words, such rehashing is not &quot;genera- tion friendly.&quot; In this paper, we describe an efficient, generati...