Supervisory control of discrete-event systems: A brief history

Computing systems are becoming more and more dynamically reconfigurable or adaptive, to be flexible w.r.t. their environment and to automate their administration. Autonomic computing proposes a general structure of feedback loop to take this into account. In this paper, we are particularly interested in approaches where this feedback loop is considered as a case of control loop where techniques stemming from Control Theory can be used to design efficient safe, and predictable controllers. This approach is emerging, with separate and dispersed effort, in different areas of the field of reconfigurable or adaptive computing, at software or architecture level. This paper surveys these approaches from the point of view of control theory techniques, continuous and discrete (supervisory), in their application to the feedback control of computing systems, and proposes detailed interpretations of feedback control loops as MAPE-K loop, illustrated with case studies.

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Feedback Control as MAPE-K loop in Autonomic Computing

We define a mixed imperative/declarative programming language: declarative contracts are enforced upon imperatively described behaviors. This paper describes the semantics of the language, making use of the notion of Discrete Controller Synthesis (DCS). We target the application domain of adaptive and reconfigurable systems: our language can serve programming closed-loop adaptation controllers, enabling flexible execution of functionalities w.r.t. changing resource and environment conditions. DCS is integrated into a1 programming language compiler, which facilitates its use by users and programmers, performing executable code generation. The tool is concretely built upon the basis of a reactive programming language compiler, where the nodes describe behaviors that can be modeled in terms of transition systems. Our compiler integrates this with a DCS tool, making it a new environment for formal methods. We define the trace semantics of our contracts language, describe its compilation and establish its correctness, and discuss implementation and examples.

/pdf/integrating-discrete-controller-synthesis-into-a-reactive-3i420jtm2e.pdf

Integrating discrete controller synthesis into a reactive programming language compiler

In this paper, we apply discrete-event system techniques to model and analyze the execution of concurrent software. The problem of interest is deadlock avoidance in shared-memory multithreaded programs. We employ Petri nets to systematically model multithreaded programs with lock acquisition and release operations. We define a new class of Petri nets, called Gadara nets, that arises from this modeling process. We investigate a set of important properties of Gadara nets, such as liveness, reversibility, and linear separability. We propose efficient algorithms for the verification of liveness of Gadara nets, and report experimental results on their performance. We also present modeling examples of real-world programs. The results in this paper lay the foundations for the development of effective control synthesis algorithms for Gadara nets.

/pdf/concurrency-bugs-in-multithreaded-software-modeling-and-1azgv29d8k.pdf

Concurrency bugs in multithreaded software: modeling and analysis using Petri nets

Computer hardware is moving from uniprocessor to multicore architectures. One problem arising in this evolution is that only parallel software can exploit the full performance potential of multicore architectures, and parallel software is far harder to write than conventional serial software. One important class of failures arising in parallel software is circular-wait deadlock in multithreaded programs. In our ongoing Gadara project, we use a special class of Petri nets, called Gadara nets, to systematically model multithreaded programs with lock allocation and release operations. In this paper, we propose an efficient optimal control synthesis methodology for ordinary Gadara nets that exploits the structural properties of Gadara nets via siphon analysis. Optimality in this context refers to the elimination of deadlocks in the program with minimally restrictive control logic. We formally establish a set of important properties of the proposed control synthesis methodology, and show that our algorithms never synthesize redundant control logic. We conduct experiments to evaluate the efficiency and scalability of the proposed methodology, and discuss the application of our results to real-world concurrent software.

https://www2.isye.gatech.edu/~spyros/publications/IEEE-CST_final_10-18-2012.pdf

Eliminating Concurrency Bugs in Multithreaded Software: A New Approach Based on Discrete-Event Control

Discrete-Event Systems (DES) theory has been successfully applied to the problem of enforcing concurrency constraints in multi-threaded applications, with concomitant guarantees regarding aggregate behaviour. Existing approaches applying DES to multi-threaded code focus on control of pre-existing, statically instantiated threads, whose creation and termination are not modelled. An extension of this case to handle dynamically instantiated and terminated threads is proposed, which makes use of elements of Dynamic DES theory to model threads whose lifetimes can be arbitrary. Process and principles are outlined, and a prototype provided.

Anthony Auer

Papers

Concurrency control generation for dynamic threads using Discrete-Event Systems

Concurrency control generation for dynamic threads using discrete-event systems