) Michael Merritt AT&T Bell Laboratories 600 Mountain Avenue Murray Hill, NJ 07974 merritt@research.att.com Francesmary Modugno School of Computer Science Carnegie Mellon University Pittsburgh, PA 15213 fmm@cs.cmu.edu Mark R. Tuttle DEC Cambridge Research Lab One Kendall Sq., Bldg. 700 Cambridge, MA 02139 tuttle@crl.dec.com Abstract In this paper, we augment the input-output automaton model in order to reason about time in concurrent systems, and we prove simple properties of this augmentation. The input-output automata model is a useful model for reasoning about computation in concurrent and distributed systems because it allows fundamental properties such as fairness and compositionality to be expressed easily and naturally. A unique property of the model is that systems are modeled as the composition of autonomous components. This paper describes a way to add a notion of time to the model in a way that preserves these properties. The result is a simple, compositional model fo...

Mutual exclusion and concurrency are two fundamental and essentially opposite features in distributed systems. However, in some applications such as Computer Supported Cooperative Work (CSCW) we have found it necessary to impose mutual exclusion on dierent groups of processes in accessing a resource, while allowing processes of the same group to share the resource. To our knowledge, no such design issue has been previously raised in the literature. In this paper we address this issue by presenting a new problem, called Congenial Talking Philosophers, to model group mutual exclusion. We also propose several criteria to evaluate solutions of the problem and to measure their performance. Finally, we provide an ecient and highly concurrent distributed algorithm for the problem in a sharedmemory model where processes communicate by reading from and writing to shared variables. The distributed algorithm meets the proposed criteria, and has performance similar to some naive but...

Ideally, distributed algorithms isolate the side-effects of faults within local neighborhoods of impact. Failure locality quanti-£es this concept as the maximum radius of impact caused by a given fault. We present new locality results for the dining philosophers problem subject to crash failures. The optimal crash locality for dining is 0 in synchronous networks, but degrades to 2 in asynchronous networks. Using the eventuallyperfect failure detector ✸P, we construct the £rst known dining algorithms with crash locality 1 under partial synchrony. These algorithms close the failure-locality complexity gap and improve the crash tolerance of resource allocation algorithms in practical networks. We prove the optimality of our results with two fundamental theorems. First, no dining solution using ✸P achieves locality 0. Second, ✸P is the weakest failure

In this paper, we augment the input-output automaton model in order to reason about time in concurrent systems, and we prove simple properties of this augmentation. The input-output automata model is a useful model for reasoning about computation in concurrent and distributed systems because it allows fundamental properties such as fairness and compositionality to be expressed easily and naturally. A unique property of the model is that systems are modeled as the composition of autonomous components. This paper describes a way to add a notion of time to the model in a way that preserves these properties. The result is a simple, compositional model for real-time computation that provides a convenient notation for expressing timing properties such as bounded fairness.

A synchronization is a mechanism allowing two or more processes to perform actions at the same time. We study the expressive power of synchronizations gathering more and more processes simultaneously. We demonstrate the nonexistence of a uniform, fully distributed translation of Milner’s CCS with synchronizations of n + 1 processes into CCS with synchronizations of n processes that retains a “reasonable ” semantics. We then extend our study to CCS with symmetric synchronizations allowing a process to perform both inputs and outputs at the same time. We demonstrate that synchronizations containing more than three input/output items are encodable in those with three items, while there is an expressivity gap between three and two. 1.