Dynamic Virtual Join Point Dispatch

Conceptually, join points are points in the execution of a program and advice is late-bound to them. We propose the notion of virtual join points that makes this concept explicit not only at a conceptual, but also at implementation level. In current implementations of aspect-oriented languages, binding is performed early, at deploy-time, and only a limited residual dispatch is executed. Current implementations fall in the categories of modifying the application code, modifying the meta-level of an application, or interacting with the application by means of events—the latter two already realizing virtual join points to some degree. We provide an implementation of an aspect-oriented execution environment that supports truly virtual join points and discuss how this approach also favors optimizations in the execution environment

Early aspects: aspect-oriented requirements engineering and architecture design

This paper reports on the third Early Aspects: Aspect-Oriented Requirements Engineering and Architecture Design Workshop, which has been held in Lancaster, UK, on March 21, 2004. The workshop included a presentation session and working sessions in which the particular topics on early aspects were discussed. The primary goal of the workshop was to focus on challenges to defining methodical software development processes for aspects from early on in the software life cycle and explore the potential of proposed methods and techniques to scale up to industrial applications

An Efficient and Flexible Implementation of Aspect-Oriented Languages

Compilers for modern object-oriented programming languages generate code in a platform independent intermediate language preserving the concepts of the source language; for example, classes, fields, methods, and virtual or static dispatch can be directly identified within the intermediate code. To execute this intermediate code, state-of-the-art implementations of virtual machines perform just-in-time (JIT) compilation of the intermediate language; i.e., the virtual instructions in the intermediate code are compiled to native machine code at runtime. In this step, a declarative representation of source language concepts in the intermediate language facilitates highly efficient adaptive and speculative optimization of the running program which may not be possible otherwise. In contrast, constructs of aspect-oriented languages - which improve the separation of concerns - are commonly realized by compiling them to conventional intermediate language instructions or by driving transformations of the intermediate code, which is called weaving. This way the aspect-oriented constructs' semantics is not preserved in a declarative manner at the intermediate language level. This representational gap between aspect-oriented concepts in the source code and in the intermediate code hinders high performance optimizations and weakens features of software engineering processes like debugging support or the continuity property of incremental compilation: modifying an aspect in the source code potentially requires re-weaving multiple other modules. To leverage language implementation techniques for aspect-oriented languages, this thesis proposes the Aspect-Language Implementation Architecture (ALIA) which prescribes - amongst others - the existence of an intermediate representation preserving the aspect-oriented constructs of the source program. A central component of this architecture is an extensible and flexible meta-model of aspect-oriented concepts which acts as an interface between front-ends (usually a compiler) and back-ends (usually a virtual machine) of aspect-oriented language implementations. The architecture and the meta-model are embodied for Java-based aspect-oriented languages in the Framework for Implementing Aspect Languages (FIAL) respectively the Language-Independent Aspect Meta-Model (LIAM) which is part of the framework. FIAL generically implements the work flows required from an execution environment when executing aspects provided in terms of LIAM. In addition to the first-class intermediate representation of aspect-oriented concepts, ALIA - and the FIAL framework as its incarnation - treat the points of interaction between aspects and other modules - so-called join points - as being late-bound to an implementation. In analogy to the object-oriented terminology for late-bound methods, the join points are called virtual in ALIA. Together, the first-class representation of aspect-oriented concepts in the intermediate representation as well as treating join points as being virtual facilitate the implementation of new and effective optimizations for aspect-oriented programs. Three different instantiations of the FIAL framework are presented in this thesis, showcasing the feasibility of integrating language back-ends with different characteristics with the framework. One integration supports static aspect deployment and produces results similar to conventional aspect weavers; the woven code is executable on any standard Java virtual machine. Two instantiations are fully dynamic, where one is realized as a portable plug-in for standard Java virtual machines and the other one, called Steamloom^ALIA , is realized as a deep integration into a specific virtual machine, the Jikes Research Virtual Machine Alpern2005. While the latter instantiation is not portable, it exhibits an outstanding performance. Virtual join point dispatch is a generalization of virtual method dispatch. Thus, well established and elaborate optimization techniques from the field of virtual method dispatch are re-used with slight adaptations in Steamloom^ALIA . These optimizations for aspect-oriented concepts go beyond the generation of optimal bytecode. Especially strikingly, the power of such optimizations is shown in this thesis by the examples of the cflow dynamic property, which may be necessary to evaluate during virtual join point dispatch, and dynamic aspect deployment - i.e., the selective modification of specific join points' dispatch. In order to evaluate the optimization techniques developed in this thesis, a means for benchmarking has been developed in terms of macro-benchmarks; i.e., real-world applications are executed. These benchmarks show that for both concepts the implementation presented here is at least circa twice as fast as state-of-the-art implementations performing static optimizations of the generated bytecode; in many cases this thesis's optimizations even reach a speed-up of two orders of magnitude for the cflow implementation and even four orders of magnitude for the dynamic deployment. The intermediate representation in terms of LIAM models is general enough to express the constructs of multiple aspect-oriented languages. Therefore, optimizations of features common to different languages are available to applications written in all of them. To proof that the abstractions provided by LIAM are sufficient to act as intermediate language for multiple aspect-oriented source languages, an automated translation from source code to LIAM models has been realized for three very different and popular aspect-oriented languages: AspectJ, JAsCo and Compose*. In addition, the feasibility of translating from CaesarJ to LIAM models is shown by discussion. The use of an extensible meta-model as intermediate representation furthermore simplifies the definition of new aspect-oriented language concepts as is shown in terms of a tutorial-style example of designing a domain specific extension to the Java language in this thesis

Debugging Scandal: The Next Generation

In 1997, the general lack of debugging tools was termed "the debugging scandal". Today, as new languages are emerging to support software evolution, once more debugging support is lagging. The powerful abstractions offered by new languages are compiled away and transformed into complex synthetic structures. Current debugging tools only allow inspection in terms of this complex synthetic structure; they do not support observation of program executions in terms of the original development abstractions. In this position paper, we outline this problem and present two emerging lines of research that ease the burden for debugger implementers and enable developers to debug in terms of development abstractions. For both approaches we identify language-independent debugger components and those that must be implemented for every new language. One approach restores the abstractions by a tool external to the program. The other maintains the abstractions by using a dedicated execution environment, supporting the relevant abstractions. Both approaches have the potential of improving debugging support for new languages. We discuss the advantages and disadvantages of both approaches, outline a combination thereof and also discuss open challenges

A qualitative assessment of modularity in CaesarJ components based on implementations of design patterns

Tese de Mestrado em Engenharia InformáticaThe advent of the Aspect-Oriented Programming (AOP) paradigm brought new features and mechanisms to support the separation of crosscutting concerns, in order to develop programs with higher modularity and consequently, higher reuse. As the paradigm matures, various aspectoriented programming languages appeared that propose varying ways to realize the paradigm’s concepts. CaesarJ is one of those aspect-oriented languages. While the majority of practical studies on AOP languages focused on the AspectJ language, the characteristics of other languages such as CaesarJ remain to be explored. The lack of research on the utilization of CaesarJ in concrete cases leads to the existence of few case studies from which to draw considerations about their strengths and shortcomings. In the past, implementations of design patterns have been used for the demonstration of the characteristics of the programming languages used to implement them. This dissertation follows a similar approach to assess CaesarJ’s support for modularity and reuse by producing CaesarJ design patterns implementations and subjecting those implementations to a qualitative analysis. This dissertation presents CaesarJ implementations of eleven Gang-of-Four pattern that serve as the basis for a qualitative analysis of the modularity degree CaesarJ enables for each pattern. A distinction is made between four levels of module reuse that the implementations support, in order to differentiate between the several levels of reuse achieved. A comparison is drawn to analogue design pattern implementations in AspectJ. Finally, general guidelines for the implementation of CaesarJ components are described

Edicts: implementing features with flexible binding times

ManuscriptIn a software product line, the binding time of a feature is the time at which one decides to include or exclude a feature from a product. Typical binding site implementations are intended to support a single binding time only, e.g., compile time or run time. Sometimes, however, a product line must support features with variable binding times. For instance, a product line may need to include both embedded system configurations, in which features are selected and optimized early, and desktop configurations, in which client programs choose features on demand. We present a new technique for implementing the binding sites of features that require flexible binding times. Our technique combines design patterns and aspect-oriented programming: a pattern encapsulates the variation point, and targeted aspects-called edicts-set the binding times of the pattern participants. We describe our approach and demonstrate its usefulness by creating a middleware product line capable of serving the desktop and embedded domains. Our product line is based on JacORB, a middleware platform with many dynamically configurable features. By using edicts to select features at compile time, we create a version of JacORB more suited to resource-constrained environments. By configuring four JacORB subsystems via edicts, we achieve a 32.2% reduction in code size. Our examples show that our technique effectively modularizes binding-time concerns, supporting both compile-time optimization and run-time flexibility as needed

Analysis of support for modularity in object teams based on design patterns

Dissertação de Mestrado em Engenharia InformáticaThe paradigm of Aspect-Oriented Programming is currently being studied and matured. Many aspectoriented languages have been proposed, including Object Teams for Java (OT/J). However, to date few studies were carried out to assess the contribution of the various languages available and compare their relative advantages and disadvantages. The aim of this dissertation is to contribute to fill this gap. In the past, implementations of design patterns in Java and AspectJ were successfully used as case studies to derive conclusions on the relative advantages and disadvantages of the language under consideration. This dissertation follows this approach, with the development of a suitable collection of examples based on the well-known Gang-of-Four design patterns. Two repositories of implementations in OT/J of the complete collection of 23 Gang-of-Four design patterns have been developed, to be used as a basis for subsequent analysis. The scenarios used for the examples are based on Java repositories by independent authors, freely available on the Web. Based on the repositories developed, an analysis of the modularizations obtained with OT/J is presented and compared with the results obtained using Java and AspectJ. OT/J provides direct language support for 3 of the patterns. 20 patterns yielded separate modules for the patterns, of which 10 modules proved to be reusable. Only in 1 of the patterns, no significant differences between Java and OT/J were obtained

FOAL 2004 Proceedings: Foundations of Aspect-Oriented Languages Workshop at AOSD 2004

Aspect-oriented programming is a paradigm in software engineering and FOAL logos courtesy of Luca Cardelli programming languages that promises better support for separation of concerns. The third Foundations of Aspect-Oriented Languages (FOAL) workshop was held at the Third International Conference on Aspect-Oriented Software Development in Lancaster, UK, on March 23, 2004. This workshop was designed to be a forum for research in formal foundations of aspect-oriented programming languages. The call for papers announced the areas of interest for FOAL as including, but not limited to: semantics of aspect-oriented languages, specification and verification for such languages, type systems, static analysis, theory of testing, theory of aspect composition, and theory of aspect translation (compilation) and rewriting. The call for papers welcomed all theoretical and foundational studies of foundations of aspect-oriented languages. The goals of this FOAL workshop were to: � Make progress on the foundations of aspect-oriented programming languages. � Exchange ideas about semantics and formal methods for aspect-oriented programming languages. � Foster interest within the programming language theory and types communities in aspect-oriented programming languages. � Foster interest within the formal methods community in aspect-oriented programming and the problems of reasoning about aspect-oriented programs. The papers at the workshop, which are included in the proceedings, were selected frompapers submitted by researchers worldwide. Due to time limitations at the workshop, not all of the submitted papers were selected for presentation. FOAL also welcomed an invited talk by James Riely (DePaul University), the abstract of which is included below. The workshop was organized by Gary T. Leavens (Iowa State University), Ralf L?ammel (CWI and Vrije Universiteit, Amsterdam), and Curtis Clifton (Iowa State University). The program committee was chaired by L?ammel and included L?ammel, Leavens, Clifton, Lodewijk Bergmans (University of Twente), John Tang Boyland (University of Wisconsin, Milwaukee), William R. Cook (University of Texas at Austin), Tzilla Elrad (Illinois Institute of Technology), Kathleen Fisher (AT&T Labs�Research), Radha Jagadeesan (DePaul University), Shmuel Katz (Technion�Israel Institute of Technology), Shriram Krishnamurthi (Brown University), Mira Mezini (Darmstadt University of Technology), Todd Millstein (University of California, Los Angeles), Benjamin C. Pierce (University of Pennsylvania), Henny Sipma (Stanford University), Mario S?udholt ( ?Ecole des Mines de Nantes), and David Walker (Princeton University). We thank the organizers of AOSD 2004 for hosting the workshop

Managing Product Line Asset Bases

Product lines are predicated on collecting assets common to the desired product portfolio, commonly known as the asset base. For many product lines, the size of asset base has become large enough to create a variety of difficulties. The techniques for managing large product line asset bases are unaddressed in the literature. This research presents new techniques that take advantage of asset base characteristics, unavailable in more general collections, to both reduce the number of assets and to organize the asset base that go beyond what is possible with other software collections. The result is an asset base that is more efficient to use. Research related to improving the organization of the asset base was performed by taking the component assets of a research SPL and arranging them based on three different organizational criteria - according to the structure of the architecture, important abstractions (Key Domain Abstractions), and product features. The three resulting organizations were then studied using four evaluation criteria - natural division of assets into groups (assets fit into the groups provided by the organization), easy to map assets to organization criteria (mapping between the selection of a particular product variant and the assets needed to produce it), reasonably sized groups, and similarly sized groups. The effectiveness of the different organizations was then compared and recommendations concerning asset base organization provided. The literature indicates that large product lines are likely to contain multiple assets that provide the same functionality, but that differ in the program context that they support. The presence of the duplicative assets creates a number of problems including organization difficulties. In a SPL these differences in program context are the result of requirements expressed at the product`s variation points. The limited differences in program context make it practical to attempt to provide a modular solution which permits the desired variation to be assembled as needed. The research explored a number of different implementation mechanisms to provide these modular variation points. The result is a recommendation on how to implement SPL variation points provided in the form of a pattern language