Mixed programming metaphors in a shared dataspace model of concurrency

Abstract

The term shared dataspace refers to the general class of models and languages in which the principal means of communication is a common, content-addressable data structure called a dataspace. Swarm is a simple language we have used as a vehicle for the investigation of the shared dataspace approach to concurrent computation. It is the first shared dataspace language to have an associated assertional-style proof system. An important feature of Swarm is its ability to bring a variety of programming paradigms under a single, unified model. In a series of related examples we explore Swarm's capacity to express shared-variable, messagepassing, and rule-based computations; to specify synchronous and asynchronous processing modes; and to accommodate highly dynamic program and data structures. Several illustrations make use of a programming construct unique to Swarm, the synchrony relation, and explain how this feature can be used to construct dynamically structured, partially synchronous computations. The paper has three parts: an overview the Swarm programming notation, an examination of Swarm programming strategies via a series of related example programs, and a discussion of the distinctive features of the shared dataspace model. A formal operational model for Swarm is presented in an appendix.

Dynamic synchrony among atomic actions

“…Dynamic synchrony: Swarm [17] is a model of concurrent computation which reduces both computation and communication to atomic transformations of a set of tuple-like entities called the dataspace. The dataspace contains data-tuples, transactions, and coupling relation entries.…”

“…Although actions cannot execute if disabled, there is no blocking in the sense of waiting for some other party to be ready. The UNITY model [5] and the Swarm model [17] go one step further; an assignment statement or transaction, respectively, is executed merely because it exists. The underlying semantics are those of a state-transition system.…”

Reasoning about synchronic groups

“…First we review the proof rules for the subset of Swarm without the synchrony relation then look at how these rules can be generalized to support the synchrony relation. (For more detail on the proof rules see [5] and on the formal operational model see [15]). The Swarm programming logics have been defined so that the theorems proved for UNITY in [4] can also be proved for Swarm.…”

“…Swarm [15] is a model which extends UNITY by permitting content-based access to data, a dynamic set of statements, and the ability to prescribe and alter the execution mode (i.e., synchronous or asynchronous) for arbitrary collections of program statements. The Swarm model is the primary vehicle for study of the shared dataspace paradigm, a class of languages and models in which the primary means for communication among the concurrent components of a program is a common, content-addressable data structure called a shared dataspace.…”

A UNITY-style programming logic for shared dataspace programs

“…Our research is exploring the implications of the shared dataspace approach and the Swarm model for algorithm development and programming methodology [21]. To facilitate formal verification of Swarm programs, we have developed an assertional programming logic and are devising proof techniques appropriate for the dynamic structure of Swarm [7,22].…”