Team Pop Art

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Section: New Results

Aspect-Oriented Programming

Participants : Pascal Fradet [contact person] , Alain Girault, Henri-Charles Blondeel.

The goal of Aspect-Oriented Programming (AOP ) is to isolate aspects (such as security, synchronization, or error handling) which cross-cut the program basic functionality and whose implementation usually yields tangled code. In AOP , such aspects are specified separately and integrated into the program by an automatic transformation process called weaving.

Although this paradigm has great practical potential, it still lacks formalization and undisciplined uses make reasoning on programs very difficult. Our work on AOP addresses these issues by studying foundational issues (semantics, analysis, verification) and by considering domain-specific aspects (availability or fault tolerance aspects) as formal properties.

Aspects Preserving Properties

Aspect Oriented Programming can arbitrarily distort the semantics of programs. In particular, weaving can invalidate crucial safety and liveness properties of the base program.

We have identified categories of aspects that preserve some classes of properties [27] . Our categories of aspects comprise, among others, observers, aborters, and confiners. For example, observers do not modify the base program's state and control-flow (e.g., persistence, profiling, and debugging aspects). These categories are defined formally based on a language independent abstract semantic framework. The classes of properties are defined as subsets of LTL for deterministic programs and CTL* for non-deterministic ones. We have formally proved that, for any program, the weaving of any aspect in a category preserves any property in the related class.

In a second step, we have designed for each aspect category a specialized aspect language which ensures that any aspect written in that language belongs to the corresponding category. These languages preserve the corresponding classes of properties by construction.

This work was conducted in collaboration with Rémi Douence from the Ascola Inria team at École des Mines de Nantes.

Resource Management and Aspects of Availability

We have proposed a domain-specific aspect language aimed at preventing denial of service caused by resource management (e.g., starvation, deadlocks, etc.) [10] . The aspects specify time or frequency limits in the allocation of resources. They can be seen as formal temporal properties on execution traces that specify availability policies. The semantics of base programs and aspects are expressed as timed automata. The main advantage of such a formal approach is two-fold:

Fault Tolerance Aspects

Here, our objective is to design a domain-specific language for specifying fault tolerance aspects as well as efficient techniques based on static analysis, program transformation, and/or instrumentation to weave them into real-time programs.

We have studied the implementation of specific fault tolerance techniques in real-time embedded systems using program transformation [1] . We are now investigating the use of fault-tolerance aspects in hardware description languages (HDL, for instance Verilog or VHDL). Our goal is to design an aspect language allowing users to specify and tune a wide range of fault tolerance techniques, while ensuring that the woven program remains synthesizable. The objective is to produce fault-tolerant circuits by specifying fault-tolerant strategies separately from the functional specifications.

This line of research is followed by Henri-Charles Blondeel in his PhD thesis, co-advised by Alain Girault and Pascal Fradet.


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