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120
EventBased Feedback Control for Deadlock Avoidance in Flexible Production Systems
 IEEE Transactions on Robotics & Automation
, 1997
"... Modern production facilities (i.e., flexible manufacturing systems) exhibit a high degree of resource sharing, a situation in which deadlocks (circular waits) can arise. Using digraph theoretic concepts we derive necessary and sufficient conditions for a deadlock occurrence and rigorously characteri ..."
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Cited by 52 (0 self)
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Modern production facilities (i.e., flexible manufacturing systems) exhibit a high degree of resource sharing, a situation in which deadlocks (circular waits) can arise. Using digraph theoretic concepts we derive necessary and sufficient conditions for a deadlock occurrence and rigorously characterize highly undesirable situations (second level deadlocks), which inevitably evolve to circular waits in the next future. We assume that the system dynamics is described by a discrete event dynamical model, whose state provides the information on the current interactions jobresources. This theoretic material allows us to introduce some control laws (named restriction policies) which use the state knowledge to avoid deadlocks by inhibiting or by enabling some transitions. The restriction policies involve small online computation costs, so they are suitable for realtime implementation. For a meaningful class of systems one of these policies is the least restrictive deadlockfree policy one ca...
A model category for the homotopy theory of concurrency
 Homology, Homotopy and Applications
"... Abstract. We construct a cofibrantly generated model structure on the category of flows such that any flow is fibrant and such that two cofibrant flows are homotopy equivalent for this model structure if and only if they are Shomotopy equivalent. This result provides an interpretation of the notion ..."
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Cited by 51 (23 self)
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Abstract. We construct a cofibrantly generated model structure on the category of flows such that any flow is fibrant and such that two cofibrant flows are homotopy equivalent for this model structure if and only if they are Shomotopy equivalent. This result provides an interpretation of the notion of Shomotopy equivalence in the framework of model
TOPOLOGICAL DEFORMATION OF HIGHER DIMENSIONAL AUTOMATA
 HOMOLOGY, HOMOTOPY AND APPLICATIONS, VOL.5(2), 2003, PP.39–82
, 2003
"... A local pospace is a gluing of topological spaces which are equipped with a closed partial ordering representing the time flow. They are used as a formalization of higher dimensional automata (see for instance [6]) which model concurrent systems in computer science. It is known [11] that there are ..."
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Cited by 51 (26 self)
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A local pospace is a gluing of topological spaces which are equipped with a closed partial ordering representing the time flow. They are used as a formalization of higher dimensional automata (see for instance [6]) which model concurrent systems in computer science. It is known [11] that there are two distinct notions of deformation of higher dimensional automata, “spatial” and “temporal”, leaving invariant computer scientific properties like presence or absence of deadlocks. Unfortunately, the formalization of these notions is still unknown in the general case of local pospaces. We introduce here a particular kind of local pospace, the “globular CWcomplexes”, for which we formalize these notions of deformations and which are sufficient to formalize
Deadlock Avoidance Policies for Automated Manufacturing Systems Using Finite State Automata
"... This chapter considers the problem of deadlock avoidance in flexibly automated manufacturing systems, one of the most prevalent supervisory control problems that challenges the effective deployment of these environments. The problem is addressed through the modeling abstraction of the (sequential) r ..."
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Cited by 45 (26 self)
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This chapter considers the problem of deadlock avoidance in flexibly automated manufacturing systems, one of the most prevalent supervisory control problems that challenges the effective deployment of these environments. The problem is addressed through the modeling abstraction of the (sequential) resource allocation system (RAS), and the pursued analysis uses concepts and results from the formal modeling framework of finite state automata (FSA). A notion of optimality is defined through the notion of maximal permissiveness, but the computation of the optimal DAP is shown to be NPHard. Hence, the last part of the chapter discusses some approaches that have been developed by the relevant research community in its effort to deal with this negative complexity result.
Integrated Concurrency Control and Recovery Mechanisms: Design and Performance Evaluation
 ACM Transactions on Database Systems
, 1985
"... In spite of the wide variety of concurrency control and recovery mechanisms proposed during the past decade, the behavior and the performance of various concurrency control and recovery mechanisms remain largely not well understood. In addition, although concurrency control and recovery mechanisms ..."
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Cited by 38 (1 self)
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In spite of the wide variety of concurrency control and recovery mechanisms proposed during the past decade, the behavior and the performance of various concurrency control and recovery mechanisms remain largely not well understood. In addition, although concurrency control and recovery mechanisms are intimately related, the interaction between them has not been adequately explored. In this paper, we take a unified view of the problems associated with concurrency control and recovery for transactionoriented multiuser centralized database management systems, and we present several integrated mechanisms. We then develop analytical models to study the behavior and compare the performance of these integrated mechanisms, and we present the results of our performance evaluation.
Homotopy and Concurrency
 Bulletin of the EATCS
, 1994
"... In this paper we give a homotopy theoretic proof of a wellknown result in database engineering: that 2phase locking is safe. The proof gives an immediate intuitive reason for why the 2phase locking condition implies safety. We point out a number of interesting open questions regarding the interpl ..."
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Cited by 33 (2 self)
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In this paper we give a homotopy theoretic proof of a wellknown result in database engineering: that 2phase locking is safe. The proof gives an immediate intuitive reason for why the 2phase locking condition implies safety. We point out a number of interesting open questions regarding the interplay between homotopy and concurrency. Keywords: Homotopy theory, serializability, 2phase locking, concurrency theory 1 Introduction What has homotopy got to do with concurrency? At first sight it seems unlikely that there should be any relationship between these two subjects. After all, homotopy theory is about continuous objects while concurrency typically deals with discrete structures. In this paper I will try to show that, on the contrary, there may be a very natural relationship between the two. Instead of making a lot of abstract statements about homotopy and concurrency I would like to work through the proof of a theorem which all database engineers learn at their Mother's knee: th...
ComponentBased Lock Allocation
"... The allocation of lock objects to critical sections in concurrent programs affects both performance and correctness. Recent work explores automatic lock allocation, aiming primarily to minimize conflicts and maximize parallelism by allocating locks to individual critical section interferences. We in ..."
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Cited by 33 (1 self)
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The allocation of lock objects to critical sections in concurrent programs affects both performance and correctness. Recent work explores automatic lock allocation, aiming primarily to minimize conflicts and maximize parallelism by allocating locks to individual critical section interferences. We investigate componentbased lock allocation, which allocates locks to entire groups of interfering critical sections. Our allocator depends on a threadbased side effect analysis, and benefits from precise pointsto and may happen in parallel information. Threadlocal object information has a small impact, and dynamic locks do not improve significantly on static locks. We experiment with a range of small and large Java benchmarks on 2way, 4way, and 8way machines, and find that a single static lock is sufficient for mtrt, that performance degrades by 10 % for hsqldb, that jbb2000 becomes mostly serialized, and that for lusearch, xalan, and jbb2005, componentbased lock allocation recovers the performance of the original program. 1.
Geometry and Concurrency: A User's Guide
, 2000
"... Introduction "Geometry and Concurrency" is not yet a wellestablished domain of research, but is rather made of a collection of seemingly related techniques, algorithms and formalizations, coming from different application areas, accumulated over a long period of time. There is currently ..."
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Cited by 32 (7 self)
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Introduction "Geometry and Concurrency" is not yet a wellestablished domain of research, but is rather made of a collection of seemingly related techniques, algorithms and formalizations, coming from different application areas, accumulated over a long period of time. There is currently a certain amount of effort made for unifying these (in particular see the article (Gunawardena, 1994)), following the workshop "New Connections between Computer Science and Mathematics" held at the Newton Institute in Cambridge, England in November 1995 (and sponsored by HP/BRIMS). More recently, the first workshop on the very same subject has been held in Aalborg, Denmark (see http://www.math.auc.dk/~raussen/admin/workshop/workshop.html where the articles of this issue, among others, have been first sketched. But what is "Geometry and Concurrency" composed of then? It is an area of research made of techniques which use geometrical reasoning for describing and solving problems
Conflict Resolution in AGV Systems
 IIE Transactions
, 2000
"... Currently, conflictfree routing in AGV systems is established by means of one of the following three approaches: (i) the problem elimination through the adoption of a segmented path flow or tandem queue configuration, (ii) the identification of imminent collisions through forward sensing and their ..."
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Cited by 21 (9 self)
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Currently, conflictfree routing in AGV systems is established by means of one of the following three approaches: (i) the problem elimination through the adoption of a segmented path flow or tandem queue configuration, (ii) the identification of imminent collisions through forward sensing and their aversion through vehicle backtracking and/or rerouting, or (iii) the imposition of zone control and extensive route preplanning, typically based on deterministic timing of the vehicle traveling and docking stages. Among these three approaches, the segmented path flowbased approach presents the highest robustness to the system stochasticities/randomness, but at the cost of restricted vehicle routings and the need for complicated handling operations. This paper proposes an alternative conflict resolution strategy that will ensure robust AGV conflict resolution, while maintaining the operational flexibility provided by free vehicle travel on arbitrarily structured guidepath networks. Specific...
PolynomialComplexity Deadlock Avoidance Policies for Sequential Resource Allocation Systems
 IEEE TRANSACTIONS ON AUTOMATIC CONTROL
, 1997
"... The development of efficient deadlock avoidance policies (DAP's) for sequential resource allocation systems (RAS) is a problem of increasing interest in the scientific community, largely because of its relevance to the design of largescale flexibly automated manufacturing systems. Much of t ..."
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Cited by 18 (2 self)
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The development of efficient deadlock avoidance policies (DAP's) for sequential resource allocation systems (RAS) is a problem of increasing interest in the scientific community, largely because of its relevance to the design of largescale flexibly automated manufacturing systems. Much of the work on this problem existing in the literature, is focused on the so called SingleUnit RAS model, which is the simplest model in the considered class of RAS. Furthermore, due to a wellestablished result stating that, even for singleunit RAS, the computation of the maximally permissive DAP is computationally intractable (NPhard), many researchers (including our group) have focused on obtaining good suboptimal policies which are computationally tractable (scalable) and provably correct. In the first part of the paper, it is shown, however, that for a large subset (in fact, a majority) of singleunit RAS, the optimal DAP can be obtained in realtime with a computational cost which is ...