Distributed Sorting

In this paper we present a distributed sorting algorithm, which is a variation on exchange sort, i.e., neighboring elements that are out of order are exchanged. We derive the algorithm by transforming a sequential algorithm into a distributed one. The transformation is guided by the distribution of the data over processes. First we discuss the case of two processes, and then the general case of one or more processes. Finally we propose a more efficient solution for the general case

The impact of asynchrony on computer architecture

The performance characteristics of asynchronous circuits are quite different from those of their synchronous counterparts. As a result, the best asynchronous design of a particular system does not necessarily correspond to the best synchronous design, even at the algorithmic level. The goal of this thesis is to examine certain aspects of computer architecture and design in the context of an asynchronous VLSI implementation. We present necessary and sufficient conditions under which the degree of pipelining of a component can be modified without affecting the correctness of an asynchronous computation. As an instance of the improvements possible using an asynchronous architecture, we present circuits to solve the prefix problem with average-case behavior better than that possible by any synchronous solution in the case when the prefix operator has a right zero. We show that our circuit implementations are area-optimal given their performance characteristics, and have the best possible average-case latency. At the level of processor design, we present a mechanism for the implementation of precise exceptions in asynchronous processors. The novel feature of this mechanism is that it permits the presence of a data-dependent number of instructions in the execution pipeline of the processor. Finally, at the level of processor architecture, we present the architecture of a processor with an independent instruction stream for branches. The instruction set permits loops and function calls to be executed with minimal control-flow overhead

Dynamic UNITY

Dynamic distributed systems, where a changing set of communicating processes must interoperate to accomplish particular computational tasks, are becoming extremely important. Designing and implementing these systems, and verifying the correctness of the designs and implementations, are difficult tasks. The goal of this thesis is to make these tasks easier. This thesis presents a specification language for dynamic distributed systems, based on Chandy and Misra's UNITY language. It extends the UNITY language to enable process creation, process deletion, and dynamic communication patterns. The thesis defines an execution model for systems specified in this language, which leads to a proof logic similar to that of UNITY. While extending UNITY logic to correctly handle systems with dynamic behavior, this logic retains the familiar UNITY operators and most of the proof rules associated with them. The thesis presents specifications for three example dynamic distributed systems to demonstrate the use of the specification language, and full correctness proofs for two of these systems and a partial correctness proof for the third to demonstrate the use of the proof logic. The thesis details a method for determining whether a system in the specification language can be transformed into an implementation in a standard programming language, as well as a method for performing this transformation on those specifications that can. This guarantees a correct implementation for any specification that can be so transformed

An Axiomatic Definition of Synchronization Primitives

The semantics of a pair of synchronization primitives is characterized by three fundamental axioms: boundedness, progress, and fairness. The class of primitives fulfilling the three axioms is semantically defined. Unbuffered communication primitives, the symmetrical P and V operations, and the usual P and V operations are proved to be the three instances of this class. The definitions obtained are used to prove a series of basic theorems on mutual exclusion, producer-consumer coupling, deadlock, and linear and circular arrangements of communicating buffer-processes. An implementation of P and V operations fulfilling the axioms is proposed