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A Framework for Comparing Models of Computation
 IEEE Transactions on ComputerAided Design of Integrated Circuits and Systems
, 1998
"... Abstract—We give a denotational framework (a “meta model”) within which certain properties of models of computation can be compared. It describes concurrent processes in general terms as sets of possible behaviors. A process is determinate if, given the constraints imposed by the inputs, there are e ..."
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Cited by 311 (63 self)
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Abstract—We give a denotational framework (a “meta model”) within which certain properties of models of computation can be compared. It describes concurrent processes in general terms as sets of possible behaviors. A process is determinate if, given the constraints imposed by the inputs, there are exactly one or exactly zero behaviors. Compositions of processes are processes with behaviors in the intersection of the behaviors of the component processes. The interaction between processes is through signals, which are collections of events. Each event is a valuetag pair, where the tags can come from a partially ordered or totally ordered set. Timed models are where the set of tags is totally ordered. Synchronous events share the same tag, and synchronous signals contain events with the same set of tags. Synchronous processes have only synchronous signals as behaviors. Strict causality (in timed tag systems) and continuity (in untimed tag systems) ensure determinacy under certain technical conditions. The framework is used to compare certain essential features of various models of computation, including Kahn process networks, dataflow, sequential processes, concurrent sequential processes with rendezvous, Petri nets, and discreteevent systems. I.
The NPcompleteness column: an ongoing guide
 Journal of Algorithms
, 1985
"... This is the nineteenth edition of a (usually) quarterly column that covers new developments in the theory of NPcompleteness. The presentation is modeled on that used by M. R. Garey and myself in our book ‘‘Computers and Intractability: A Guide to the Theory of NPCompleteness,’ ’ W. H. Freeman & ..."
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Cited by 218 (0 self)
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This is the nineteenth edition of a (usually) quarterly column that covers new developments in the theory of NPcompleteness. The presentation is modeled on that used by M. R. Garey and myself in our book ‘‘Computers and Intractability: A Guide to the Theory of NPCompleteness,’ ’ W. H. Freeman & Co., New York, 1979 (hereinafter referred to as ‘‘[G&J]’’; previous columns will be referred to by their dates). A background equivalent to that provided by [G&J] is assumed, and, when appropriate, crossreferences will be given to that book and the list of problems (NPcomplete and harder) presented there. Readers who have results they would like mentioned (NPhardness, PSPACEhardness, polynomialtimesolvability, etc.) or open problems they would like publicized, should
Design of Embedded Systems: Formal Models, Validation, and Synthesis
 PROCEEDINGS OF THE IEEE
, 1999
"... This paper addresses the design of reactive realtime embedded systems. Such systems are often heterogeneous in implementation technologies and design styles, for example by combining hardware ASICs with embedded software. The concurrent design process for such embedded systems involves solving the ..."
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Cited by 122 (9 self)
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This paper addresses the design of reactive realtime embedded systems. Such systems are often heterogeneous in implementation technologies and design styles, for example by combining hardware ASICs with embedded software. The concurrent design process for such embedded systems involves solving the specification, validation, and synthesis problems. We review the variety of approaches to these problems that have been taken.
On Describing the Behavior and Implementation of Distributed Systems
, 1981
"... A simple, basic and general model for describing both the (inputoutput) behavior and the implementation of distributed systems is presented. An important feature of the model is the separation of the machinery used to describe the implementation and the behavior. This feature makes the model potent ..."
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Cited by 57 (18 self)
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A simple, basic and general model for describing both the (inputoutput) behavior and the implementation of distributed systems is presented. An important feature of the model is the separation of the machinery used to describe the implementation and the behavior. This feature makes the model potentially useful for design specification of systems and of subsystems.
Runtime checking of multithreaded applications with visual threads
 In Proceedings of the 7th International SPIN Workshop on SPIN Model Checking and Software Verification
, 2000
"... ..."
Detecting Deadlocks In Concurrent Systems
 IN CONCUR’98: CONCURRENCY THEORY (NICE
, 1998
"... We study deadlocks using geometric methods based on generalized process graphs [11], i.e., cubical complexes or HigherDimensional Automata (HDA) [23, 24, 30, 35], describing the semantics of the concurrent system of interest. A new algorithm is described and fully assessed, both theoretically a ..."
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Cited by 50 (12 self)
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We study deadlocks using geometric methods based on generalized process graphs [11], i.e., cubical complexes or HigherDimensional Automata (HDA) [23, 24, 30, 35], describing the semantics of the concurrent system of interest. A new algorithm is described and fully assessed, both theoretically and practically and compared with more wellknown traversing techniques. An implementation is
Algebraic Topology And Concurrency
 Theoretical Computer Science
, 1998
"... This article is intended to provide some new insights about concurrency theory using ideas from geometry, and more specifically from algebraic topology. The aim of the paper is twofold: we justify applications of geometrical methods in concurrency through some chosen examples and we give the mathem ..."
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Cited by 47 (12 self)
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This article is intended to provide some new insights about concurrency theory using ideas from geometry, and more specifically from algebraic topology. The aim of the paper is twofold: we justify applications of geometrical methods in concurrency through some chosen examples and we give the mathematical foundations needed to understand the geometric phenomenon that we identify. In particular we show that the usual notion of homotopy has to be refined to take into account some partial ordering describing the way time goes. This gives rise to some new interesting mathematical problems as well as give some common grounds to computerscientific problems that have not been precisely related otherwise in the past. The organization of the paper is as follows. In Section 2 we explain to which extent we can use some geometrical ideas in computer science: we list a few of the potential or well known areas of application and try to exemplify some of the properties of concurrent (and distributed) systems we are interested in. We first explain the interest of using some geometric ideas for semantical reasons. Then we take the example of concurrent databases with the problem of finding deadlocks and with some aspects of serializability theory. More general questions about schedules can be asked as well and related to some geometric considerations, even for scheduling microinstructions (and not only coarsegrained transactions as for databases). The final example is the one of faulttolerant protocols for distributed systems, where subtle scheduling properties go into play. In Section 3 we give the first few definitions needed for modeling the topological spaces arising from Section 2. Basically, we need to define a topological space containing all traces of executions of the concu...
Dihomotopy as a Tool in State Space Analysis
, 2002
"... Recent geometric methods have been used in concurrency theory for quickly finding deadlocks and unreachable states, see [14] for instance. The reason why these methods are fast is that they contain in germ ingredients for tackling the statespace explosion problem. In this paper we show how this can ..."
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Cited by 19 (6 self)
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Recent geometric methods have been used in concurrency theory for quickly finding deadlocks and unreachable states, see [14] for instance. The reason why these methods are fast is that they contain in germ ingredients for tackling the statespace explosion problem. In this paper we show how this can be made formal. We also give some hints about the underlying algorithmics. Finally, we compare with other wellknown methods for coping with the statespace explosion problem.
LPVM: A Step Towards Multithread PVM
 Journal of Parallel and Distributed Computing , submitted special
, 1997
"... LPVM (Lightweightprocess PVM) system is an experimental PVM version which supports the use of lightweightprocess or threads as the basic unit of parallelism. It was designed to study potential performance improvements and implementation issues required by multithreaded messagepassing systems. The ..."
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Cited by 13 (0 self)
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LPVM (Lightweightprocess PVM) system is an experimental PVM version which supports the use of lightweightprocess or threads as the basic unit of parallelism. It was designed to study potential performance improvements and implementation issues required by multithreaded messagepassing systems. The current version of LPVM was implemented on SMPs using the native threads and is designed to be threadsafe. Initial test results on SUN SMP are compared to standard PVM. 1 Introduction With the help of parallel programming software systems such as PVM [1] and MPI [2], looselycoupled distributed computing systems, usually composed of networks of workstations [3], have been very popular for many years as a costeffective alternative to highperformance computing. Since 1994, the increasing availability of affordable SMP (shared memory multiprocessor or symmetrical multiprocessor) systems have begun to emerge as the lower end of highperformance computing. Clusters of SMPs, also called SPPs ...
Integrating Fast Network Communication with a UserLevel Thread Scheduler
 University of Malta
, 2002
"... In operating systems, traditional methods of network communication incur high overheads and usually block the process performing the communication. This means that if a process has some communication in progress, it cannot perform further computation until the communication is complete, even thou ..."
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Cited by 4 (0 self)
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In operating systems, traditional methods of network communication incur high overheads and usually block the process performing the communication. This means that if a process has some communication in progress, it cannot perform further computation until the communication is complete, even though the CPU is free to be used during this time. This dissertation deals with the integration of a communication system with a userlevel thread scheduler. In this way, while one userlevel thread is waiting for a particular communication operation to complete, other userlevel threads can perform some computation, e#ectively overlapping communication with computation.