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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 245 (54 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 & Co ..."
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Cited by 188 (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 106 (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.
Runtime Checking of Multithreaded Applications with Visual Threads
 In 7th SPIN Workshop, volume 1885 of LNCS
, 2000
"... . Multithreaded applications are notoriously difficult to design and build while avoiding defects. Many of Compaq's customers need to employ threads to implement highperformance, scalable applications that address their needs in business and science. In order to ensure their success using thread ..."
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Cited by 54 (0 self)
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. Multithreaded applications are notoriously difficult to design and build while avoiding defects. Many of Compaq's customers need to employ threads to implement highperformance, scalable applications that address their needs in business and science. In order to ensure their success using threads, Compaq provides a runtime debugging and analysis tool for multithreaded applications called Visual Threads. This paper describes the automatic runtime checking for multithreaded applications incorporated in Visual Threads. 1 Introduction While the performance of computer systems continues to improve at a rapid rate, many problems in science and business continue to outstrip the ability of a single processor. This has given rise to computer systems built using Symmetric Multiprocessing (SMP), and programming interfaces to enable an application to enlist those processors. One such programming interface standard is IEEE POSIX 1003.11996, which is commonly referred to as pthreads [1]....
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 46 (11 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 40 (8 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 17 (5 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 3 (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.
A Pragmatic Approach to Conflict
 In (Tessier and Chaudron
, 1998
"... . This paper proposes an alternative approach to that of considering conflict as a foremost problem to be solved in a system made up of multiple entities, by suggesting to integrate it without necessarily running a serious risk. This position is supported by preliminary experimental results and by i ..."
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Cited by 2 (1 self)
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. This paper proposes an alternative approach to that of considering conflict as a foremost problem to be solved in a system made up of multiple entities, by suggesting to integrate it without necessarily running a serious risk. This position is supported by preliminary experimental results and by interdisciplinary research reviews. 1 INTRODUCTION The work presented in this paper fits in the framework of autonomous agents, also referred to as bottomup artificial intelligence or behaviorbased artificial intelligence in the literature [2], [22]. Our concern concentrates on the study of autonomous agents looked at from the point of view of their adaptive capabilities. We take up a methodology which follows an engineering trend that can be characterized by: 1. a bioinspired approach, drawing its models from neurobiology, evolutionary biology and the study of animal societies, and participating in the concept of embodiment of intelligence now surfacing in artificial intelligence [1...