ion and Modularity Mechanisms for Concurrent Computing Gul Agha, Svend Frølund, WooYoung Kim, Rajendra Panwar, Anna Patterson, and Daniel Sturman Department of Computer Science 1304 W. Springfield Avenue University of Illinois at Urbana-Champaign Urbana, IL 61801, USA Email: !agha---frolund---wooyoung---raju---annap---sturman?@cs.uiuc.edu 1 Introduction The transition from sequential to parallel and distributed computing has been widely accepted as a major paradigm shift occurring in Computer Science. It has been observed that the sequential programming model is inadequate for parallel and distributed computing. At a conceptual level, one can compare the fundamental intuition between sequential and concurrent computing as follows: ffl The sequential programming model essentially defines a computation as a sequence of instructions which manipulate a global store. The standard abstraction mechanism for sequential programs is procedures. Procedures glue a sequence of instructions; they a...

. We have developed language support for the expression of multiobject coordination. In our language, coordination patterns can be specified abstractly, independent of the protocols needed to implement them. Coordination patterns are expressed in the form of constraints that restrict invocation of a group of objects. Constraints are defined in terms of the interface of the objects being invoked rather than their internal representation. Invocation constraints enforce properties, such as temporal ordering and atomicity, that hold when invoking objects in a group. A constraint can permanently control access to a group of objects, thereby expressing an inherent access restriction associated with the group. Furthermore, a constraint can temporarily enforce access restrictions during the activity of individual clients. In that way, constraints can express specialized access schemes required by a group of clients. 1 Motivation Coordination of activities is a fundamental aspect of programm...

This paper presents the design and implementation of a model for combining object oriented programming and constraint programming. This model aims to be an aid in the development of computer graphics applications that use these two programming paradigms. We first identify the typical aspects of the paradigms and how they conflict with each other. Next, we show how these conflicts are solved in the model by radically separating the object oriented paradigm from the constraint paradigm. The communication between these two systems is then managed by a third party. A prototype of the model was implemented, based on a coordination language a language for managing concurrent, independent processes. This allows us to build an ideal implementation. Although this ideal implementation does not yield the necessary performance in speed, it clearly demonstrates that the model provides an appropriate way for setting up an application that incorporates object oriented programming as well as constrain...

This paper discusses the complexity of constraint satisfaction, and the effect of information hiding. On the one hand, powerful constraint satisfaction is necessarily global, and tends to break information hiding. On the other hand, preserving strict information hiding increases the complexity of constraint satisfaction, or severely limits the power of the constraint solver. Ultimately, under strict information hiding, constraint satisfaction on complex objects cannot be guaranteed.