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One of the main challenges in developing a software system is to assure that its properties fulfill the specifications. In the context of this paper, we are especially interested in timing properties. Model-based software verification is one of the approaches to achieve this. However, model-based verification requires expressive models of software systems and deriving such models is not a trivial task. Although there are a few model derivation tool proposals for the purpose of model-checking timing properties, these are dedicated tools supporting a selected set of verification techniques and as such they are not explicitly designed for coping with new demands. This paper presents a framework that derives models from Java programs in an automated way for analyzing timing properties. The framework has the following properties that are not provided by the previous proposals: (1) Efficiency in model development, (2) consistency of models with software, (3) expressiveness of models, (4) scalability and (5) extensibility of the model derivation process.

Run-time assertion checking of multithreaded programs is challenging, as assertion evaluation should not interfere with the execution of other threads. This paper describes the prototype implementation of a run-time assertion checker that achieves this by evaluating assertions over snapshots of the state, instead of over the live state. Our prototype e-OpenJML, an extension to OpenJML, provides an easy to use, safe and interference-free evaluation of JML specifications in multithreaded programs. To achieve this, it integrates e-STROBE, our extension to the STROBE framework for asynchronous assertion evaluation. e-STROBE prevents all possible interferences between assertion evaluation and other program threads, which the original STROBE can not. It also simplifies evaluating assertions that relate the value of expressions in multiple states.

In this paper, we report preliminary ideas from our project called “Time Performance Improvement With Parallel Processing Systems‿ (TIPS). In the TIPS project, we plan to take advantage of multi-core platforms for performance improvement by parallelizing a complex soft real-time application. In order to increase the timing performance, one needs to adapt the optimizations on the critical execution paths of an application which are both significantly time consuming and important from user requirements' perspective. In this work, we present an approach how to detect critical paths in a target application.

The history of programming languages shows a continuous search for new composition mechanisms to find better ways for structuring increasingly complex software systems into modules that can be developed and reused independently. Composition mechanisms can address various types of dependencies among modules, e.g., inheritance, delegation, aggregation, design patterns, contracts, explicit protocols, or domain-specific compositions. However, most languages adopt a fixed set of composition mechanisms, usually with explicit notation and predefined semantics. In case a language does not provide any mechanisms with the desired compositional behavior, programmers may need to write workarounds or introduce the new composition mechanism through macros, libraries, frameworks or language extensions. This workshop intends to stimulate research in programming languages and software development by exploring the notion that today's languages with their limited set of composition mechanisms is insufficient. Instead we should allow compositions that support more flexibility, adopt a wide variety of compositions, domain-specific and tailored compositions, or programmable compositions of various program artifacts.

Domain Specific Languages (DSLs) are programming languages customized for a problem/solution domain, which allow development of software modules in high-level specifications. Code generation is a common practice for making DSL programs executable: A DSL specification is transformed to a functionally equivalent GPL (general-purpose programing language) representation. Integrating the module generated from a DSL specification to a base system poses a challenge, especially in a case where the DSL and the base system are developed independently. In this paper we describe the problem of integrating domain-specific modules to a system non-intrusively and promote loose coupling between these to allow software evolution. We present our on-going work on aspect-oriented language mechanisms for defining object selectors and object adapters as a solution to this problem.

Historically, programming languages have been—benevolent—dictators: reducing all possible semantics to specific ones offered by a few built-in language constructs. Over the years, some programming languages have freed the programmers from the restrictions to use only built-in libraries, built-in data types, and builtin type-checking rules. Even though—arguably—such freedom could lead to anarchy, or people shooting themselves in the foot, the contrary tends to be the case: a language that does not allow for extensibility is depriving software engineers of the ability to construct proper abstractions and to structure software in the most optimal way. Therefore the software becomes less structured and maintainable than would be possible if the software engineer could express the behavior of the program with the most appropriate abstractions. The idea proposed by this paper is to move composition from built-in language constructs to programmable, first-class abstractions in a language. We discuss several prototypes of the Co-op language, which show that it is possible, with a relatively simple model, to express a wide range of compositions as first-class concepts.

Runtime verification aims to check whether an application executes its behaviour as specified. Thereby the active execution trace of an application is checked in terms of the actual execution context; diagnosis and, possibly, recovery actions are taken when the specification is violated. In today’s practices, software is increasingly distributed over multiple processes, potentially running at different locations. This is supported by middleware that, to some extent, allows implementing applications in a distribution-transparent way. To enable effective runtime verification in distributed software we focus in this paper on three requirements: (1) distribution-transparent specification of software behaviour, as software is also implemented in such a way, (2) end-to-end verification of behaviour, and (3) automatic generation of verification modules for arbitrary process and distribution structures. We present a novel runtime verification approach satisfying these requirements and present its implementation in the EventChaser system. Furthermore we present an approach that at least minimizes the distribution-awareness of specifications to an acceptable level for software not using supported middleware for inter-process communication.

Historically, programming languages have been—although benevolent—dictators: fixing a lot of semantics into built-in language constructs. Over the years, (some) programming languages have freed the programmers from restrictions to use only built-in libraries, built-in data types, or built-in type checking rules. Even though, arguably, such freedom could lead to anarchy, or people shooting themselves in the foot, the contrary tends to be the case: a language that does not allow for extensibility, is depriving software engineers from the ability to construct proper abstractions and to structure software in the most optimal way. Instead, the software becomes less structured and maintainable than would be possible if the software engineer could express the behavior of the program with the most appropriate abstractions. The new idea proposed by this paper is to move composition from built-in language constructs to programmable, first-class abstractions in the language. As an emerging result, we present the Co-op concept of a language, which shows that it is possible with a relatively simple model to express a wide range of compositions as first-class concepts.

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.

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.

Programming-language research has introduced a considerable number of advanced-dispatching mechanisms in order to improve modularity. Advanced-dispatching mechanisms allow changing the behavior of a function without modifying their call sites and thus make the local behavior of code less comprehensible. Debuggers are tools, thus needed, which can help a developer to comprehend program behavior but current debuggers do not provide inspection of advanced- dispatching-related language constructs. In this paper, we present a debugger which extends a traditional Java debugger with the ability of debugging an advanced-dispatching language constructs and a user interface for inspecting this.

Programming-language research produces a significant number of new programming styles to improve the composability of programs. This increases re-usability as well as other quality characteristics. But although they offer interesting composition concepts, new programming languages are rarely used because IDE support, which developers are used to, is missing. Examples of such IDE support are the visualization of call hierarchies or interactive debugging. While some languages, e.g., AspectJ, eventually reach a more mature level with elaborate IDE integration, not all language designers are able to invest this much effort towards IDE integration. Furthermore, the IDE integration of AspectJ also has its limitations; when debugging, the developer is confronted with synthetic code with no exact correspondence in the source code. As a result, the developer needs to understand the transformations performed by the compiler. Finally, some information invariably gets lost during weaving, e.g., the ability to map code evaluating pointcut designators to their definition in the source code. In this paper, we propose to implement generic IDE tools for programming languages that provide advanced dispatching mechanisms. Such languages, including predicate dispatching and pointcut-advice languages, can be mapped to our execution model, called ALIA. The same execution model can then drive debugging functionality as well as static IDE services.

Aspect Oriented Modeling (AOM) techniques facilitate separate modeling of concerns and allow for a more flexible composition of these than traditional modeling techniques. While this improves the understandability of each submodel, in order to reason about the behavior of the composed system and to detect conflicts among submodels, automated tool support is required. Current techniques for con°ict detection among aspects generally have at least one of the following weaknesses. They require to manually model the abstract semantics for each system; or they derive the system semantics from code assuming one specific aspect-oriented language. Defining an extra semantics model for verification bears the risk of inconsistencies between the actual and the verified design; verifying only at implementation level hinders fixing errors in earlier phases. We propose a technique for fully automatic detection of conflicts between aspects at the model level; more specifically, our approach works on UML models with an extension for modeling pointcuts and advice. As back-end we use a graph-based model checker, for which we have defined an operational semantics of UML diagrams, pointcuts and advice. In order to simulate the system, we automatically derive a graph model from the diagrams. The result is another graph, which represents all possible program executions, and which can be verified against a declarative specification of invariants. To demonstrate our approach, we discuss a UML-based AOM model of the "Crisis Management System" and a possible design and evolution scenario. The complexity of the system makes conflicts among composed aspects hard to detect: already in the case of two simulated aspects, the state space contains 623 different states and 9 different execution paths. Nevertheless, in case the right pruning methods are used, the state-space only grows linearly with the number of aspects; therefore, the automatic analysis scales.

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.

Runtime enforcement aims at verifying the active execution trace of executing software against formally specified properties of the software, and enforcing the properties in case that they are violated in the active execution trace. Enforcement mechanism of individual properties may interfere with each other, causing the overall behavior of the executing software to be erroneous. As the number and the complexity of the properties to be enforced increase, manual detection of the inferences becomes an error-prone and effort-consuming task. Hence, we aim at providing a framework for automatic detection of interferences. As the initial steps to create such a framework, in this paper we first provide formal definitions of an enforcement mechanism and enforcement operators. Second, we define a rule set to detect the interference among properties.

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.

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.