The Reflex Sandbox : an experimentation environment for an aspect-oriented Kernel

Reflex es un núcleo versátil para la programación orientada aspectos en Java. Provee de las abstracciones básicas, estructurales y de comportamiento, que permiten implementar una variedad de técnicas orientadas a aspectos. Esta tesis estudia dos tópicos fundamentales. En primer lugar, el desarrollo formal, utilizando el lenguaje Haskell, de las construcciones fundamentales del modelo Reflex para reflexión parcial de comportamiento. Este desarrollo abarca el diseño de un lenguaje, llamado Kernel, el cual es una extensión reflexiva de un lenguaje orientado a objetos simple. La semántica operacional del lenguaje Kernel es presentada mediante una máquina de ejecución abstracta. El otro tópico fundamental que estudia esta tesis es validar que el modelo de reflexión parcial de comportamiento es suficientemente expresivo para proveer de semántica a un subconjunto del lenguaje AspectJ. Con este fin, se desarrolló el Reflex Sandbox: un ambiente de experimentación en Haskell para el modelo Reflex. Tanto el desarrollo formal del modelo de reflexión parcial de comportamiento como la validación del soporte de AspectJ, son estudiados en el contexto del Reflex Sandbox. La validación abarca la definición de un lenguaje orientado a aspectos que caracteriza el enfoque de AspectJ a la programación orientada a aspectos, así como la definición de su máquina de ejecución abstracta. También se presenta un compilador que transforma programas escritos en este lenguaje al lenguaje Kernel. Este proceso de compilación provee los fundamentos para entender como dicha transformación puede ser realizada. El proceso de compilación también fue implementado en Java, pero transformando programas AspectJ a programas Reflex. También se presentan mediciones preliminares del desempeño de un programa compilado y ejecutado en Reflex y un programa compilado, y ejecutado con el compilador AspectJ

A framework for requirements engineering for context-aware services

Context-aware services, especially when made available to mobile devices, constitute an interesting but very challenging domain. It poses fundamental problems for both requirements engineering, software architecture, and their relationship. We propose a novel, reflection-based framework for requirements engineering for this class of applications. The framework addresses the key difficulties in this field, such as changing context and changing requirements. We report preliminary work on this framework and suggest future directions

A Case for Custom, Composable Composition Operators

Programming languages typically support a fixed set of com- position operators, with fixed semantics. This may impose limits on software designers, in case a desired operator or semantics are not supported by a language, resulting in suboptimal quality characteristics of the designed software system. We demonstrate this using the well-known State design pattern, and propose the use of a composition infrastructure that allows the designer to define custom, composable composition operators. We demonstrate how this approach improves several quality factors of the State design pattern, such as reusability and modularity, while taking a reason- able amount of effort to define the necessary pattern-related code

Open Programming Language Interpreters

Context: This paper presents the concept of open programming language interpreters and the implementation of a framework-level metaobject protocol (MOP) to support them. Inquiry: We address the problem of dynamic interpreter adaptation to tailor the interpreter's behavior on the task to be solved and to introduce new features to fulfill unforeseen requirements. Many languages provide a MOP that to some degree supports reflection. However, MOPs are typically language-specific, their reflective functionality is often restricted, and the adaptation and application logic are often mixed which hardens the understanding and maintenance of the source code. Our system overcomes these limitations. Approach: We designed and implemented a system to support open programming language interpreters. The prototype implementation is integrated in the Neverlang framework. The system exposes the structure, behavior and the runtime state of any Neverlang-based interpreter with the ability to modify it. Knowledge: Our system provides a complete control over interpreter's structure, behavior and its runtime state. The approach is applicable to every Neverlang-based interpreter. Adaptation code can potentially be reused across different language implementations. Grounding: Having a prototype implementation we focused on feasibility evaluation. The paper shows that our approach well addresses problems commonly found in the research literature. We have a demonstrative video and examples that illustrate our approach on dynamic software adaptation, aspect-oriented programming, debugging and context-aware interpreters. Importance: To our knowledge, our paper presents the first reflective approach targeting a general framework for language development. Our system provides full reflective support for free to any Neverlang-based interpreter. We are not aware of any prior application of open implementations to programming language interpreters in the sense defined in this paper. Rather than substituting other approaches, we believe our system can be used as a complementary technique in situations where other approaches present serious limitations

Bridging the Gap between Machine and Language using First-Class Building Blocks

High-performance virtual machines (VMs) are increasingly reused for programming languages for which they were not initially designed. Unfortunately, VMs are usually tailored to specific languages, offer only a very limited interface to running applications, and are closed to extensions. As a consequence, extensions required to support new languages often entail the construction of custom VMs, thus impacting reuse, compatibility and performance. Short of building a custom VM, the language designer has to choose between the expressiveness and the performance of the language. In this dissertation we argue that the best way to open the VM is to eliminate it. We present Pinocchio, a natively compiled Smalltalk, in which we identify and reify three basic building blocks for object-oriented languages. First we define a protocol for message passing similar to calling conventions, independent of the actual message lookup mechanism. The lookup is provided by a self-supporting runtime library written in Smalltalk and compiled to native code. Since it unifies the meta- and base-level we obtain a metaobject protocol (MOP). Then we decouple the language-level manipulation of state from the machine-level implementation by extending the structural reflective model of the language with object layouts, layout scopes and slots. Finally we reify behavior using AST nodes and first-class interpreters separate from the low-level language implementation. We describe the implementations of all three first-class building blocks. For each of the blocks we provide a series of examples illustrating how they enable typical extensions to the runtime, and we provide benchmarks validating the practicality of the approaches

MobiPADS: a reflective middleware for context-aware mobile computing

distributed computing services that essentially abstract the underlying network services to a monolithic “black box. ” In a mobile operating environment, the fundamental assumption of middleware abstracting a unified distributed service for all types of applications operating over a static network infrastructure is no longer valid. In particular, mobile applications are not able to leverage the benefits of adaptive computing to optimize its computation based on current contextual situations. In this paper, we introduce the Mobile Platform for Actively Deployable Service (MobiPADS) system. MobiPADS is designed to support context-aware processing by providing an executing platform to enable active service deployment and reconfiguration of the service composition in response to environments of varying contexts. Unlike most mobile middleware, MobiPADS supports dynamic adaptation at both the middleware and application layers to provide flexible configuration of resources to optimize the operations of mobile applications. Within the MobiPADS system, services (known as mobilets) are configured as chained service objects to provide augmented services to the underlying mobile applications so as to alleviate the adverse conditions of a wireless environment. Index Terms—Middleware, mobile applications, mobile computing support services, mobile environments.

Using a loadtime metaobject protocol to enforce access control policies upon user-level compiled code

This thesis evaluates the use of a loadtime metaobject protocol as a practical mechanism for enforcing access control policies upon applications distributed as user-level compiled code. Enforcing access control policies upon user-level compiled code is necessary because there are many situations where users are vulnerable to security breaches because they download and run potentially untrustworthy applications provided in the form of user-level compiled code. These applications might be distributed applications so access control for both local and distributed resources is required. Examples of potentially untrustworthy applications are Browser plug-ins, software patches, new applications, or Internet computing applications such as SETI@home. Even applications from trusted sources might be malicious or simply contain bugs that can be exploited by attackers so access control policies must be imposed to prevent the misuse of resources. Additionally, system administrators might wish to enforce access control policies upon these applications to ensure that users use them in accordance with local security requirements. Unfortunately, applications developed externally may not include the necessary enforcement code to allow the specification of organisation-specific access control policies. Operating system security mechanisms are too coarse-grained to enforce security policies on applications implemented as user-level code. Mechanisms that control access to both user-level and operating system-level resources are required for access control policies but operating system mechanisms only focus on controlling access to system-level objects. Conventional object-oriented software engineering can be used to use existing security architectures to enforce access control on user-level resources as well as system-resources. Common techniques are to insert enforcement within libraries or applications, use inheritance and proxies. However, these all provide a poor separation of concerns and cannot be used with compiled code. In-lined reference monitors provide a good separation of concerns and meet criteria for good security engineering. They use object code rewriting to control access to both userlevel and system-level objects by in-lining reference monitor code into user-level compiled code. However, their focus is upon replacing existing security architectures and current implementations do not address distributed access control policies. Another approach that does provide a good separation of concerns and allows reuse of existing security architectures are metaobject protocols. These allow constrained changes to be made to the semantics of code and therefore can be used to implement access control policies for both local and distributed resources. Loadtime metaobject protocols allow metaobject protocols to be used with compiled code because they rewrite base level classes and insert meta-level interceptions. However, these have not been demonstrated to meet requirements for good security engineering such as complete mediation. Also current implementations do not provide distributed access control. This thesis implements a loadtime metaobject protocol for the Java programming language. The design of the metaobject protocol specifically addresses separation of concerns, least privilege, complete mediation and economy of mechanism. The implementation of the metaobject protocol, called Kava, has been evaluated by implementing diverse security policies in two case studies involving third-party standalone and distributed applications. These case studies are used as the basis of inferences about general suitability of using loadtime reflection for enforcing access control policies upon user-level compiled code.EThOS - Electronic Theses Online ServiceGBUnited Kingdo