Christoph Bockisch

Virtual machine support for dynamic join points

A widespread implementation approach for the join point mechanism of aspect-oriented languages is to instrument areas in code that match the static part of pointcut designators, inserting dynamic checks for that part of matching that depends on run-time conditions, if needed. For performance reasons, such dynamic checks should be avoided whenever possible. One way to do so is to postpone weaving of advice calls until run-time, when conditions determining the emergence of join points hold. This calls for fluid code---code that adapts itself to the join point emergence at run-time, and suggests that AOP concepts should be integrated into the execution model underlying a VM. In this paper, we present first steps toward such an integration in Steamloom, an extension of IBMs Jikes Research Virtual Machine. Steamloom is fairly restricted, but our initial experimental results indicate that aspect-aware VMs and fluid code are promising w.r.t performance. While the focus in this paper is on performance, there are other advantages of aspect-aware VMs to be investigated in the future.

Expressive pointcuts for increased modularity

In aspect-oriented programming, pointcuts are used to describe crosscutting structure. Pointcuts that abstract over irrelevant implementation details are clearly desired to better support maintainability and modular reasoning. We present an analysis which shows that current pointcut languages support localization of crosscutting concerns but are problematic with respect to information hiding. To cope with the problem, we present a pointcut language that exploits information from different models of program semantics, such as the execution trace, the syntax tree, the heap, static type system, etc., and supports abstraction mechanisms analogous to functional abstraction. We show how this raises the abstraction level and modularity of pointcuts and present first steps toward an efficient implementation by means of a static analysis technique.

Adapting virtual machine techniques for seamless aspect support

Current approaches to compiling aspect-oriented programs are inefficient. This inefficiency has negative effects on the productivity of the development process and is especially prohibitive for dynamic aspect deployment. In this work, we present how well-known virtual machine techniques can be used with only slight modifications to support fast aspect deployment while retaining runtime performance. Our implementation accelerates dynamic aspect deployment by several orders of magnitude relative to mainstream aspect-oriented environments. We also provide a detailed comparison of alternative implementations of execution environments with support for dynamic aspect deployment.

An execution layer for aspect-oriented programming languages

Language mechanisms deserve language implementation effort. While this maxim has led to sophisticated support for language features specific to object-oriented, functional and logic programming languages, aspect-oriented programming languages are still mostly implemented using postprocessors. The Steamloom virtual machine, based on IBMs Jikes RVM, provides support for aspect-oriented programming at virtual machine level. A bytecode framework called BAT was integrated with the Jikes RVM to replace its bytecode management logic. While preserving the functionality needed by the VM, BAT also allows for querying application code for join point shadows, avoiding redundancy in bytecode representation. Performance measurements show that an AOP-enabled virtual machine like Steamloom does not inflict unnecessary performance penalties on a running application; when it comes to executing AOP-related operations, there even are significant performance gains compared to other approaches.

A flexible architecture for pointcut-advice language implementations

Current implementations for aspect-oriented programming languages map the aspect-oriented concepts of source programs to object-oriented bytecode. This hinders execution environments with dedicated support for such concepts in applying their optimizations, as they have to recover the original aspect definition from bytecode. To address this representational gap we propose an architecture for implementations of pointcut-advice languages where aspect-oriented concepts are preserved as first-class entities. In this architecture, compilers generate a model of the crosscutting which is executed by virtual machines. In this paper we discuss a meta-model for aspect-oriented concepts and a virtual machine-integrated weaver for the meta-model. As a proof of concept, we also provide an instantiation of the meta-model with the AspectJ language and an AspectJ compiler complying with the proposed architecture. We also discuss how preexisting high-performance optimizations of aspect-oriented concepts benefit from the proposed architecture.

Applying the Composition Filter Model for Runtime Verification of Multiple-Language Software

Complex software, especially the embedded one, is composed of multiple collaborating subsystems that are possibly developed in multiple languages. To verify the behavior of such software, a run-time verification system must deal with multiple-language environments both in its specifications and in its generated runtime verification modules. In this paper, we present the E-Chaser runtime verification system, whose front-end provides language-independent specifications, and whose backend provides an extendable toolset with new implementation languages. E-Chaser is built based on the Composition Filter Model and extends it with the notion of synchronization messages and synchronization filters to verify the synchronization properties of multiple subsystems. The first prototype of EChaser was successfully used to verify various properties

A design method for modular energy-aware software

Nowadays reducing the overall energy consumption of software is important. A well-known solution is extending the functionality of software with energy optimizers, which monitor the energy consumption of software and adapt it accordingly. To make such extensions manageable and to cope with the complexity of the software, modular design of energy-aware software is necessary. Therefore, this paper proposes a dedicated design method for energy-aware software.

An In-Depth Look at ALIA4J

New programming languages supporting advanced modularization mechanisms are often implemented as transformations to the imperative intermediate representation of an already established language. But while their core constructs largely overlap in semantics, re-using the corresponding transformations requires re-using their syntax as well; this is limiting. In the ALIA4J approach, we identified dispatching as fundamental to most modularization mechanisms and provide a meta-model of dispatching as a rich, extensible intermediate language. Based on this meta-model, one can modularly implement the semantics of dispatching-related constructs. From said constructs a single execution model can then be derived which facilitates interpretation, bytecode generation, and even optimized machine-code generation. We show the suitability of our approach by mapping five popular languages to this meta-model and find that most of their constructs are shared across multiple languages. We furthermore present implementations of the three different execution strategies together with a generic visual debugger available to any ALIA4J-based language implementation. Intertwined with this paper is a tutorial-style running example that illustrates our approach.

A fine-grained debugger for aspect-oriented programming

To increase modularity, aspect-oriented programming provides a mechanism based on implicit invocation: An aspect can influence runtime behavior of other modules without the need that these modules refer to the aspect. Recent studies show that a significant part of reported bugs in aspect-oriented programs are caused exactly by this implicitness. These bugs are difficult to detect because aspect-oriented source code elements and their locations are transformed or even lost after compilation. We investigate four dedicated fault models and identify ten tasks that a debugger should be able to perform for detecting aspect-orientation-specific faults. We show that existing debuggers are not powerful enough to support all identified tasks because the aspect-oriented abstractions are lost after compilation. This paper describes the design and implementation of a debugger for aspect-oriented languages using a dedicated intermediate representation preserving the abstraction level of aspect-oriented source code. We define a debugging model which is aware of aspect-oriented concepts. Based on the model, we implement a user interface with functionalities supporting the identified tasks, like visualizing pointcut evaluation and program composition.

Towards modular resource-aware applications

Resource optimization is an increasingly important requirement in the design and implementation of software systems. It is applied to improve both environmental sustainability and usability of resource-constrained devices. This paper claims that to achieve more modular resource-aware applications, the resource utilization of components must explicitly be modeled. Due to shortcomings of existing modeling languages, we propose a notation for the resource consumption of components and we illustrate the suitability of this notation by means of two real-world examples. We observe that explicitly modeling resource consumption has as result that resource consumption information is scattered across and tangled with the functional services of components.