Synchronization: a Formal Approach.

Synchronization is the coordination of concurrent processes that occurs in most complex software systems. The term "synchronization" has been widely used since the inception of multi-programming, but its definition has remained vague and somewhat intuitive. As a result, there are a number of apparently contradictory results in the literature. In addition, there has been a proliferation of new synchronization constructs, each designed to solve a specific problem in a specific environment. In order to evaluate synchronizing primitives and to come to a better underst and ing of synchronization itself, it is necessary to establish a formal framework in which synchronization, specific synchronization problems and synchronizing constructs can be defined precisely. In this thesis, we present such a framework. The formal framework introduced here consists of a general model of concurrent computation together with a formalization of the concept of simulation. The model of concurrent computation differs from previous models in that synchronizing constraints are applied to sequences of operations, rather than to single operations. This allows the accurate representation of high-level, non-atomic constructs such as monitors and serializers. In fact, all common synchronizing constructs can be given precise, uniform definitions in terms of this model. The formalization of simulation, as a behavior-preserving mapping between systems, is used to compare synchronization across systems. It differs from previous formalizations in its more realistic treatment of process blocking. With this definition, it is shown that P and V operations are as powerful as PV chunk operations--a result that is intuitively correct but which seems to contradict the previous work of Lipton. In addition, we show that P's and V's are as powerful as monitors--a result that is significant because it is the first formal treatment of a high-level construct. The model and the formalization of simulation that we present together provide a consistent and powerful framework for investigating synchronization.Ph.D.Computer scienceUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/158236/1/8116220.pd

Interface-based support for model coupling: Spatial representation and compatibility issues

Model coupling is a nontrivial task that is not adequately supported in existing frameworks. Our long-term goal is to support the fast-prototyping of model couplings, enabling scientists to quickly experiment with a variety of linkings without having to make an upfront investment in reprogramming. The centerpiece of our framework, the Potential Coupling Interface (PCI), must expose all the characteristics of a model that are relevant to model coupling, but what are those characteristics? To explore different couplings, and to identify the relevant model characteristics, we conducted a study of 14 hydrological models and the pairwise couplings between them. We found that the model characteristics relevant to coupling lie in four dimensions: space, time, structure, and data. Models of the same phenomena often had similar characteristics, making it feasible to replace them within a coupling when appropriate for specific sites. We also found that resolving differences along the four dimensions, particularly with respect to space, can be complex