Rémi Douence

Composition, reuse and interaction analysis of stateful aspects

Aspect-Oriented Programming promises separation of concerns at the implementation level. However, aspects are not always orrthogonal and aspect interaction is a fundamental problem. In this paper, we extend previous work on a generic framework for the formal definition and interaction analysis of stateful aspects. We propose three important extensions which enhance expressivity while preserving static analyzability of interactions. First, we provide support for variables in aspects in order to share information between different execution points. This allows the definition of more precise aspects and to avoid detection of spurious conflicts. Second, we introduce generic composition operators for aspects. This enables us to provide expressive support for the resolution of conflicts among interacting aspects. Finally, we offer a means to define applicability conditions for aspects. This makes interaction analysis more precise and paves the way for reuse of aspects by making explicit requirements on contexts in which aspects must be used.

A Framework for the Detection and Resolution of Aspect Interactions

Aspect-Oriented Programming (AOP) promises separation of concerns at the implementation level. However, aspects are not always orthogonal and aspect interaction is an important problem. Currently there is almost no support for the detection and resolution of such interactions. The programmer is responsible for identifying interactions between conflicting aspects and implementing conflict resolution code.In this paper, we propose a solution to this problem based on a generic framework for AOP. The contributions are threefold: we present a formal and expressive crosscut language, two static conflict analyses and some linguistic support for conflict resolution.

A Formal Definition of Crosscuts

Crosscutting, i.e. relating different program points is one of the key notions of Aspect-Oriented Programming. In this article, we consider a general and operational model for crosscutting based on execution monitors.A domain-specific language for the definition of crosscuts constitutes the core of the article. The semantics of this language is formally defined by means of parser operators matching event patterns in execution traces. We define an operational semantics of the matching process by means of rules relating the operators.The use of the language is exemplified by several sophisticated crosscut detinitions. We sketch a prototype implementation in JAVA which has been systematically derived from the language definition.

An expressive aspect language for system applications with Arachne

C applications, in particular those using operating system level services, frequently comprise multiple crosscutting concerns: network protocols and security are typical examples of such concerns. While these concerns can partially be addressed during design and implementation of an application, they frequently become an issue at runtime, e.g., to avoid server downtime. A deployed network protocol might not be efficient enough and may thus need to be replaced. Buffer overflows might be discovered that imply critical breaches in the security model of an application. A prefetching strategy may be required to enhance performance.While aspect-oriented programming seems attractive in this context, none of the current aspect systems is expressive and efficient enough to address such concerns. This paper presents a new aspect system to provide a solution to this problem. While efficiency considerations have played an important part in the design of the aspect language, the language allows aspects to be expressed more concisely than previous approaches. In particular, it allows aspect programmers to quantify over sequences of execution points as well as over accesses through variable aliases. We show how the former can be used to modularize the replacement of network protocols and the latter to prevent buffer overflows. We also present an implementation of the language as an extension of Arachne, a dynamic weaver for C applications. Finally, we present performance evaluations supporting that Arachne is fast enough to extend high performance applications, such as the Squid web cache.

Concurrent aspects

Aspect-Oriented Programming (AOP) promises the modularization of so-called crosscutting functionalities in large applications. Currently, almost all approaches to AOP provide means for the description of sequential aspects that are to be applied to a sequential base program. In particular, there is no formally-defined concurrent approach to AOP, with the result that coordination issues between aspects and base programs as well as between aspects cannot precisely be investigated.This paper presents Concurrent Event-based AOP (CEAOP), which addresses this issue. Our contribution can be detailed as follows. First, we formally define a model for concurrent aspects which extends the sequential Event-based AOP approach. The definition is given as a translation into concurrent specifications using Finite Sequential Processes (FSP), thus enabling use of the Labelled Transition System Analyzer (LTSA) for formal property verification. Further, we show how to compose concurrent aspects using a set of general composition operators. Finally, we sketch a Java prototype implementation for concurrent aspects, which generates coordination specific code from the FSP model defining the concurrent AO application.

No Java without caffeine: A tool for dynamic analysis of Java programs

To understand the behavior of a program, a maintainer reads some code, asks a question about this code, conjectures an answer, and searches the code and the documentation for confirmation of her conjecture. However, the confirmation of the conjecture can be error-prone and time-consuming because the maintainer has only static information at her disposal. She would benefit from dynamic information. In this paper, we present Caffeine, an assistant that helps the maintainer in checking her conjecture about the behavior of a Java program. Our assistant is a dynamic analysis tool that uses the Java platform debug architecture to generate a trace, i.e., an execution history, and a Prolog engine to perform queries over the trace. We present a usage scenario based on the n-queens problem, and two real-life examples based on the Singleton design pattern and on the composition relationship.

Debugging and testing middleware with aspect-based control-flow and causal patterns

Many tasks that involve the dynamic manipulation of middleware and large-scale distributed applications, such as debugging and testing, require the monitoring of intricate relationships of execution events that trigger modifications to the executing system. Furthermore, events often are of interest only if they occur as part of specific execution traces and not all possible non-deterministic interleavings of events in these traces. Current techniques and tools for the definition of such manipulations provide only very limited support for such event relationships and do not allow to concisely define restrictions on the interleaving of events. In this paper, we argue for the use of aspect-based high-level programming abstractions for the definition of relationships between execution events of distributed systems and the control of non-deterministic interleavings of events. Concretely, we provide the following contributions: we (i) motivate that such abstractions improve on current debugging and testing methods for middleware, (ii) introduce corresponding language support for pointcuts and advice defined in terms of causal event sequences by extending an existing aspect-oriented system for the dynamic manipulation of distributed systems, and (iii) evaluate our approach in the context of the debugging and testing of Java-based middlewares, in particular, JBoss Cache for replicated caching.

Expressive scoping of distributed aspects

Dynamic deployment of aspects brings greater flexibility and reuse potential, but requires proper means for scoping aspects. Scoping issues are particularly crucial in a distributed context: adequate treatment of distributed scoping is necessary to enable the propagation of aspect instances across host boundaries and to avoid inconsistencies due to unintentional spreading of data and computations in a distributed system. We motivate the need for expressive scoping of dynamically-deployed distributed aspects by an analysis of the deficiencies of current approaches for distributed aspects. Extending recent work on deployment strategies for non-distributed aspects, we then introduce a set of high-level strategies for specifying locality of aspect propagation and activation, and illustrate the corresponding gain in expressiveness. We present the operational semantics of our proposal using Scheme interpreters, first introducing a model of distributed aspects that covers the range of current proposals, and then extending it with dynamic aspect deployment. This work shows that, given some extensions to their original execution model, deployment strategies are directly applicable to the expressive scoping of distributed aspects.

A Generic Reification Technique for Object-Oriented Reflective Languages

Computational reflection is gaining interest in practical applications as witnessed by the use of reflection in the Java programming environment and recent work on reflective middleware. Reflective systems offer many different reflection programming interfaces, the so-called Meta-Object Protocols (MOPs). Their design is subject to a number of constraints relating to, among others, expressive power, efficiency and security properties. Since these constraints are different from one application to another, it would be desirable to easily provide specially-tailored MOPs.In this paper, we present a generic reification technique based on program transformation. It enables the selective reification of arbitrary parts of object-oriented meta-circular interpreters. The reification process is of fine granularity: individual objects of the run-time system can be reified independently. Furthermore, the program transformation can be applied to different interpreter definitions. Each resulting reflective implementation provides a different MOP directly derived from the original interpreter definition.

A systematic study of functional language implementations

We introduce a unified framework to describe, relate, compare, and classify functional language implementations. The compilation process is expressed as a succession of program transformations in the common framework. At each step, different transformations model fundamental choices. A benefit of this approach is to structure and decompose the implementation process. The correctness proofs can be tackled independently for each step and amount to proving program transformations in the functional world. This approach also paves the way to formal comparisons by making it possible to estimate the complexity of individual transformations or compositions of them. Our study aims at covering the whole known design space of sequential functional language implementations. In particular, we consider call-by-value, call-by-name, call-by-need reduction strategies as well as environment- and graph-based implementations. We describe for each compilation step the diverse alternatives as program transformations. In some cases, we illustrate how to compare or relate compilation techniques, express global optimizations, or hybrid implementations. We also provide a classification of well-known abstract machines.