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IEEETRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS,VOL.3,NO.l,JANUARY 1992 121 Short Notes A Dynamic Information-Structure Mutual Exclusion Algorithm for Distributed Systems Mukesh Singhal Abstract-h this paper, we present a dynamic information-structure mutual exclusion algorithm for distributed systems whose information- structure evolves with time as sites learn about the state of the system through messages. An interesting feature of the algorithm is that it adapts itself to heterogeneous or fluctuating traffic conditions to optimize the performance (the number of messages exchanged). We study the performance by simulation technique and compare to the performance a well-known [14]. We discuss the impact of message loss and site failures on the algorithm and propose methods to tolerate these failures. Index Terms-Deadlock, dynamic information-structures, fault toler- ance, mutual exclusion, performance, recovery, starvation. I. INTRODUCTION In this paper, we consider the problem of mutual exclusion in distributed systems. A distributed system consists of a collection of geographically dispersed autonomous sites, say Sr Sz. S,, . which are connected by a communication network. We assume that the sites do not share any memory and communicate completely by message passing. Message propagation delay is finite but unpre- dictable and between any pair of sites messages are delivered in the order they arc sent. For the ease of presentation, we initially assume that the underlying communication network is reliable and sites do not crash. Later, we discuss the consequences of message loss and site failures on the operation of the algorithm and propose methods for recovery from these failures. Over the last decade, several algorithms to achieve mutual exclu- sion in distributed systems have been proposed. Based upon their underlying principle to achieve mutual exclusion, these algorithms can be divided into two classes: token-based and nontoken-based. Nontoken-based algorithms use two or more successive phases of message exchanges to determine which site should enter the critical section (CS) next [l], [h], (81, [14]. Algorithms in [3], [7], [lo], [12], [17]-[19] are token-based where a unique token (also known as the PRIVILEGE message [ 121, [18]) is shared among the sites such that possession of the token gives a site the authority to execute its CS. Singular existence of token in these algorithms implies the enforcement of mutual exclusion in distributed systems. Out of all the existing algorithms, only the algorithms in [I], [2], [5], [7], [ll], [12], [14], and [17] have discussed fault-tolerant aspects. Objective of the Paper The information-structure of an algorithm describes which pro- cesses maintain state information about what other processes and from which processes a process must request permission before it enters the critical section [15]. Most existing mutual exclusion algorithms for distributed systems use static information-structure Manuscript received March 28, 1989; revised December 12, 1990. The author is with the Department of Computer and Information Science,
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This note was uploaded on 05/11/2011 for the course CS 591 taught by Professor Annieliu during the Spring '11 term at SUNY Stony Brook.

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