Proposes an improved extendible hashing and bucket multi-versioning method, achieving a higher concurrency. In our improved extendible hashing, the global depth and directory entries are asynchronously modified to red...
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Proposes an improved extendible hashing and bucket multi-versioning method, achieving a higher concurrency. In our improved extendible hashing, the global depth and directory entries are asynchronously modified to reduce lock conflicts on the directory. Furthermore, bucket multi-versioning enables read-only access to a bucket which is being split. simulation studies show that these two methods provide speedup in proportion to the number of processors and enable concurrent insertions and retrievals to be performed without either one affecting the other.
Incremental, parallel development of distributed real-time systems is difficult. Architectural techniques and software tools developed at the Jet Propulsion Laboratory's (JPL's) Flight System Testbed (FST) mak...
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Incremental, parallel development of distributed real-time systems is difficult. Architectural techniques and software tools developed at the Jet Propulsion Laboratory's (JPL's) Flight System Testbed (FST) make feasible the integration of complex systems in various stages of development. In particular, two techniques are used: a strict layering architecture for organization of independent subsystems, and a distributed, low-overhead, asynchronous messaging system. These techniques were developed in a few user-months and have proven their usefulness in a spacecraft integration test and simulation environment.
The vortex method in the simulation of 2D incompressible flows with complex interacting circulations is very attractive if compared with other nowadays widespread methods. However, the vortex method is computationally...
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The vortex method in the simulation of 2D incompressible flows with complex interacting circulations is very attractive if compared with other nowadays widespread methods. However, the vortex method is computationally very expensive and suggests the adoption of suitably powerful computing units. Our group analysed some parallelisation techniques of the algorithm, in order to obtain the best performances on a dedicated parallel architecture. A promising architecture was simulated in a PVM (parallel Virtual Machine) environment to identify correctness and efficiency of the selected choices. The implementation of the most promising one on a Special Purpose Computer (SPC) based on i860 Risc Intel units is in progress. The porting of the parallelised algorithm into the SPC will result into a low-cost system, completely available to the user, with expected performances comparable to those of modern supercomputers.
A data parallel model for the parallelsimulation of cellular neural networks is proposed. This approach is based on the SPMD (single-program multiple data) model and utilizes the highly specialized programming enviro...
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A data parallel model for the parallelsimulation of cellular neural networks is proposed. This approach is based on the SPMD (single-program multiple data) model and utilizes the highly specialized programming environment of the Vienna FORTRAN compilation system (VFCS) for the parallel process. It allows an easy development of the simulation system as a sequential program attributed with data distribution information shifting the difficult parallel process to the compiler. An analysis of the run-time behavior of the developed parallel programs for the simulation of cellular neural networks for different data distribution schemes is given, which justifies the efficiency of the proposed approach.
We present an execution model for parallelsimulation of a distributed shared memory architecture. The model captures the processor-memory interaction and abstracts the memory subsystem. Using this model we show how p...
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We present an execution model for parallelsimulation of a distributed shared memory architecture. The model captures the processor-memory interaction and abstracts the memory subsystem. Using this model we show how parallel, on-line, partially-ordered memory traces can be correctly predicted without interacting with the memory subsystem. We also outline a parallel optimistic memory simulator that uses these traces, finds a global order among all events, and returns correct data and timing to each processor. A first evaluation of the amount of concurrency that our model can extract for an ideal multiprocessor shows that processors may execute relatively long instruction sequences without violating the causality constraints. However parallelsimulation efficiency is highly dependent on the memory consistency model and the application characteristics.
In currently-used paradigms for system development, knowledge about the objects in the system's environment is used to derive algorithms that relate events in the environment to actions. This results in implicit r...
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In currently-used paradigms for system development, knowledge about the objects in the system's environment is used to derive algorithms that relate events in the environment to actions. This results in implicit representation of the original knowledge in the operational system. In the majority of cases, there are only very limited mechanisms for controlling these built-in behaviours, whereas for powerful decision support it is essential to be able to "experiment" both with various hypotheses about the behaviour of real-world entities and with the system's own possible actions. Such simulation-like operation necessitates an explicit representation of behavioural models. A new paradigm for the development of reactive systems is therefore proposed in which the behavioural models are explicitly represented and the user of the system is given direct control over these models. This allows the user to easily express both hypotheses about the intentions of real-world entities, and the system's own potential actions that are necessary to meet the mission goals. Through the control of simulated time, the possible evolutions of the environment can then be studied directly.
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