Experts in a field regularly apply a defined set of rules or procedures to carry out a problem-solving task or analysis on a given problem. Often the problem can be represented as a computer model, be it mathematical, chemical, or physics based, and so on. It would certainly be advantageous for a domain expert who is not proficient in software development to express solutions to problems in a domain-specific notation that can be executed as a program. Many new ideas aim to make software development easier and shift the development role closer to the end-user. One such means of development is the use of a small, intuitive programming language called a Domain-Specific Language (DSL.) This dissertation examines a generic approach to constructing a Virtual Machine (VM) to provide the runtime semantics for a particular DSL. It proposes a generic, object-oriented framework, called a VM Framework, in which to build a VM by subtyping abstract instruction and environment classes that are part of the VM Framework. The subtyped classes constitute an environment and an interface called an instruction set architecture and the instructions can access and operate on the environment in a deterministic way to provide the runtime semantics of a DSL program. Both instruction classes and environment classes encapsulate functionality of an existing domain, represented programmatically as a namespace construct. The namespace is home to related classes that provide the various concepts inherent of a domain. These are concepts understood by a domain expert and in this dissertation it is shown how they are exposed as DSL constructs. With the use of compiler writing tools, a compiler can be created for a DSL that generates an appropriate instruction sequence that can be executed by the VM. The grammar of the DSL is shown to feature constructs that allow a domain expert to express concepts of the underlying domain in an intuitive manner. The dissertation details how a VM is configured for a specific set of instructions and an environment. Instruction sets and environments can be extended creating VMs with additional semantics for DSLs that are similar, or contain subsets of semantics of other DSLs. The languages are intended to be intuitive and it is shown using examples how a specific DSL program is mapped to an instruction sequence with the instruction set architecture and environment in mind. Comparative performance in relation to other DSL implementations, including a hard-coded approach of a VM and an interpreted approach are also provided. The VM Framework is proven to be most effective in rapidly prototyping a DSL for a particular problem domain. The dissertation also provides examples of DSLs such as a real-valued expression language and a scene description language that uses a ray-tracer for rendering geometric objects onto a canvas. It is shown how the scene description language is an extension to the real-valued expression language in terms of their underlying VMs. All DSL grammars are provided. / Dissertation (MSc (Computer Science))--University of Pretoria, 2007. / Computer Science / MSc / unrestricted

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O modelo de programação baseado em atores é frequentemente utilizado para o desenvolvimento de grandes aplicações e sistemas. Podemos citar como exemplo o serviço de bate-papo do Facebook ou ainda o WhatsApp. Estes sistemas dão suporte a milhares de usuários conectados simultaneamente levando em conta estritas restrições de desempenho e interatividade. Tais sistemas normalmente são amparados por infraestruturas de hardware com processadores de múltiplos núcleos. Normalmente, máquinas deste porte são baseadas em uma estrutura de memória compartilhada hierarquicamente (NUMA - Non-Uniform Memory Access). Nossa análise dos atuais ambientes de execução para atores e a pesquisa na literatura mostram que poucos estudos sobre a adequação deste ambientes a essas plataformas hierárquicas foram conduzidos. Estes ambientes de execução normalmente assumem que o espaço de memória é uniforme o que pode causar sérios problemas de desempenho. Nesta tese nós estudamos os desafios enfrentados por um ambiente de execução para atores quando da sua execução nestas plataformas. Estudamos particularmente os problemas de gerenciamento de memória, de escalonamento e de balanceamento de carga. Neste documento nós também analisamos e caracterizamos as aplicações baseadas no modelo de atores. Tal análise nos permitiu evidenciar o fato de que a execução de benchmarks e aplicações criam estruturas de comunicação peculiares entre os atores. Tais peculiaridades podem, então, ser utilizadas pelos ambientes de execução para otimizar o seu desempenho. A avaliação dos grafos de comunicação e a implementação da prova de conceito foram feitas utilizando um ambiente de execução real, a máquina virtual da linguagem Erlang. A linguagem Erlang utiliza o modelo de atores para concorrência com uma sintaxe clara e consistente. As modificações que nós efetuamos nesta máquina virtual permitiram uma melhora significativa no desempenho de certas aplicações através de uma melhor afinidade de comunicação entre os atores. O escalonamento e o balanceamento de carga também foram melhorados graças à utilização do conhecimento sobre o comportamento da aplicação e sobre a plataforma de hardware. / The actor model is present in several mission-critical systems, such as those supporting WhatsApp and Facebook Chat. These systems serve thousands of clients simultaneously, therefore demanding substantial computing resources usually provided by multi-processor and multi-core platforms. Non-Uniform Memory Access (NUMA) architectures account for an important share of these platforms. Yet, research on the suitability of the current actor runtime environments for these machines is very limited. Current runtime environments, in general, assume a flat memory space, thus not performing as well as they could. In this thesis we study the challenges hierarchical shared memory multi-core platforms present to actor runtime environments. In particular, we investigate aspects related to memory management, scheduling, and load-balancing. In this document, we analyze and characterize actor based applications to, in light of the above, propose improvements to actor runtime environments. This analysis highlighted the existence of peculiar communication structures. We argue that the comprehension of these structures and the knowledge about the underlying hardware architecture can be used in tandem to improve application performance. As a proof of concept, we implemented our proposal using a real actor runtime environment, the Erlang Virtual Machine (VM). Concurrency in Erlang is based on the actor model and the language has a consistent syntax for actor handling. Our modifications to the Erlang VM significantly improved the performance of some applications thanks to better informed decisions on scheduling and on load-balancing.

Adaptive software becomes more and more important as computing is increasingly context-dependent. Runtime adaptability can be achieved by dynamically selecting and applying context-specific code. Role-oriented programming has been proposed as a paradigm to enable runtime adaptive software by design. Roles change the objects’ behavior at runtime and thus allow adapting the software to a given context. However, this increased variability and expressiveness has a direct impact on performance and memory consumption. We found a high overhead in the steady-state performance of executing compositions of adaptations. This paper presents a new approach to use run-time information to construct a dispatch plan that can be executed efficiently by the JVM. The concept of late binding is extended to dynamic function compositions. We evaluated the implementation with a benchmark for role-oriented programming languages leveraging context-dependent role semantics achieving a mean speedup of 2.79× over the regular implementation.

The thesis deals with selection of infrastructure virtualization platform focusing on containerization with sandboxing support and with following examination of its difculty. The work begins with an explanation of the basic technologies such as: virtualization, cloud computing and containerization, along with their representatives, that mediate the technology. A special scope is defned for cloud computing platforms: Kubernetes, OpenStack and OpenShift. Futhermore, the most suitable platform is selected and deployed using own technique so that it fullflls all the conditions specifed by thesis supervisor. Within the difculty testing of the selected platform, there are created scripts (mainly in the Bash language) for scanning system load, creating scenarios, stress testing and automation.

This diploma thesis formally defines the Object Oriented Petri Nets and presents term a virtual machine. Then it introduces the concept of Object Oriented Petri Nets Virtual Machine. Finally, project describes a procedure for implementation of the OOPN Virtual Machine.

This report presents the SHAP platform consisting of its microarchitecture and its implementation of the Java Virtual Machine (JVM). Like quite a few other embedded implementations of the Java platform, the SHAP microarchitecture relies on an instruction set architecture based on Java bytecode. Unlike them, it, however, features a design with well-encapsulated components autonomously managing their duties on rather high abstraction levels. Thus, permanent runtime duties are transferred from the central computing core to concurrently working components so that it can actually spent a larger fraction of time executing application code. The degree of parallelity between the application and the runtime implementation is increased. Currently, the stack and heap management including the automatic garbage collection are implemented this way. After detailing the design of the microarchitecture, the SHAP implementation of the Java Virtual Machine is described. A major focus is laid on the presentation of the layout and the use of the runtime data structures representing the various language abstractions provided by Java. Also, the boot sequence starting the JVM is described.

Purpose – The purpose of this paper is to explore the possibility to effectivize local networks and databases using unikernels and compare this to containers. This could also apply to reliability of executing programs the same way on different hardware in software development. Method – Two experiments have been performed to explore if the purpose could be realized, quantitative data have been gatheredand displayed in both cases. Python-scripts have been used to start C-scripts, acting client and server. Algorithms have been timed running in unikernels as well as in containers along with compared measurements of memory in multiple simultaneous instantiations. Findings – Intermittent response times spiked made the data hard to parse correctly. Containers had a lower average response time when running lighter algorithms. The average response times of unikernels dives below that of containers when heavier programs are simulated. Few minor bugs were discovered in Unikraft unikernels. Implications – unikernels havecharacteristics that make them more suitable for certain tasks compared to their counterpart, this is also true for containers. Unikraft unikernels are unstable which makes it seem like containers are faster during lighter simulations. Unikernels are onlyfaster and more secure if the tools used to build them does so in a manner that makes them stable. Limitations – The lack of standards, the lack of a support community together with the fact that unikernels is a small and niche field means that unikernels have a relatively high learning curve. Keywords – Unikraft, Unikernels, Docker, Container / Syfte – Syftet med denna studie är att undersöka möjligheten att effektivisera lokala nätverk och databaser med hjälp av unikernels och att jämföra denna möjlighet med containrar. Detta kan även gälla utveckling av programvara för att säkerställa att programvaran exekveras på servern på exakt samma sätt som den tidigare gjort lokalt på utvecklarens lokala dator. Metod – Två experiment utförs för att undersöka om det går besvara syftet, kvantitativa data samlas in i båda fallen, datan är även redovisad kvantitativt. Python-script används föratt starta C-script som agerar klient och server. Tidtagning på algoritmer i unikernels respektive containrar samt minnesanvändning vid multipel instansiering mättes för att analyseras och jämföras. Resultat – Intermittenta svarstids-toppar gjorde datan från unikernels svår att korrekt utvärdera. Containrar hade ett lägre medelvärde på svarstider vid mindre krävande algoritm-användning. Unikernels medelvärde dyker under container-svarstiderna när mer krävande program simuleras. Några små buggar upptäcktesi Unikraft unikernels. Implikationer – Unikernels har egenskaper som gör de mer passande för vissa uppgifter jämfört med dess motsvarighet medan detsamma gäller för Containrar. Unikraft unikernels är instabila och ger därfören bild av att containrar vidmindre processorkrävande program faktiskt är snabbare än unikernels. Unikernels är bara snabbare och säkrare i den mån verktyget som bygger dem, gör det på ett sätt att de är stabila. Begränsningar – Avsaknaden av standarder, avsaknaden av ett communitysom kan svara på frågor tillsammans med att unikernelsär ett litet och nischat fält gör att unikernels har en relativ hög inlärningskurva. Nyckelord – Unikernel, Unikraft, Container, Docker

Dans les systèmes cloud géographiquement distribués, un défi majeur auquel sont confrontés les fournisseurs de cloud consiste à optimiser et à configurer leurs infrastructures. En particulier, cela consiste à trouver un emplacement optimal pour les machines virtuelles (VMs) afin de minimiser les coûts tout en garantissant une bonne performance du système. De plus, en raison des fluctuations de la demande et des modèles de trafic, il est essentiel d'ajuster dynamiquement le schéma de placement des VMs en utilisant les techniques de migration des VMs. Cependant, malgré ses avantages apportés, dans le contexte du Cloud géo-distribué, la migration des VMs génère un trafic supplémentaire dans le réseau backbone ce qui engendre la dégradation des performances des applications dans les centres de données (DCs) source et destination. Par conséquent, les décisions de migration doivent être bien étudiés et basées sur des paramètres précis. Dans ce manuscrit, nous étudions les problèmes d'optimisation liés au placement, à la migration et à l'ordonnancement des VMs qui hébergent des applications hautement corrélées et qui peuvent être placés dans des DCs géo-distribués. Dans ce contexte, nous proposons un outil de gestion de DC autonome basé sur des modèles d'optimisation en ligne et hors ligne pour gérer l'infrastructure distribuée du Cloud. Notre objectif est de minimiser le volume du trafic global circulant entre les différents DCs du système.Nous proposons également des modèles d'optimisation stochastiques et déterministes pour traiter les différents modèles de trafic de communication. En outre, nous fournissons des algorithmes quasi-optimaux qui permettent d'avoir la meilleure séquence de migration inter-DC des machines virtuelles inter-communicantes. En plus, nous étudions l'impact de la durée de vie des VMs sur les décisions de migration afin de maintenir la stabilité du Cloud. Enfin, nous utilisons des environnements de simulation pour évaluer et valider notre approche. Les résultats des expériences menées montrent l'efficacité de notre approche / In geo-distributed cloud systems, a key challenge faced by cloud providers is to optimally tune and configure their underlying cloud infrastructure. An important problem in this context, deals with finding an optimal virtual machine (VM) placement, minimizing costs while at the same time ensuring good system performance. Moreover, due to the fluctuations of demand and traffic patterns, it is crucial to dynamically adjust the VM placement scheme over time. Hence, VM migration is used as a tool to cope with this problem. However, despite the benefits brought by VM migration, in geo-distributed cloud context, it generates additional traffic in the backbone links which may affect the application performance in both source and destination DCs. Hence, migration decisions need to be effective and based on accurate parameters. In this work, we study optimization problems related to the placement, migration and scheduling of VMs hosting highly correlated and distributed applications within geo-distributed DCs. In this context, we propose an autonomic DC management tool based on both online and offline optimization models to manage the distributed cloud infrastructure. Our objective is to minimize the overall expected traffic volume circulating between the different DCs of the system. To deal with different types of communication traffic patterns, we propose both deterministic and stochastic optimization models to solve VM placement and migration problem and to cope with the uncertainty of inter-VM traffic. Furthermore, we propose near-optimal algorithms that provide with the best inter-DCs migration sequence of inter-communicating VMs. Along with that, we study the impact of the VM's lifetime on the migration decisions in order to maintain the stability of the cloud system. Finally, to evaluate and validate our approach, we use experimental tests as well as simulation environments. The results of the conducted experiments show the effectiveness of our proposals

<p>This thesis presents an in-depth investigation into the opportunities of optimizing the performance (throughput) of fuzzing on Java Virtual Machine (JVM)-based languages. The study identifies five main areas for potential optimization, each of which contributes to the performance bottlenecks in the existing state-of-the-art Java fuzzer, Jazzer.</p> <p><br></p> <p>Firstly, the use of coverage probes is recognized as costly due to the native method call, including call frame generation and destruction, while it only performs a simple byte increment. Secondly, the probes may become exhausted, which subsequently cease to generate signals for new interesting inputs, while the associated costs persist. Thirdly, the scanning of the coverage map is expensive, particularly for targets with a large loaded bytecode. Given that test inputs can only execute a portion of these, the probes for most bytecodes are scanned repeatedly without generating any signals, indicating a need for a more structured coverage map design to skip the code probes effectively. Lastly, exception handling in JVM is costly as it automatically fills in the stack trace whenever an exception object is created, even when most targets don't utilize this information. </p> <p><br></p> <p>The study then designs and implements optimization techniques for these opportunities. We believe we provide the optimal solution for the first opportunity, while better optimizations could be proposed for the second, third, and fourth. The collective improvement brought about by these implementations is on average 138% and up to 441% in throughput. This work, thus, offers valuable insights into enhancing the efficiency of fuzz testing in JVM languages and paves the way for further research in optimizing other areas of JVM-based-language fuzzing performance.</p>