A distributed mutual exclusion algorithm for mobile computing environments

Abstract

Mobile computing systems are expected to revolutionize the way computers are used. Mobile hosts have small memory, a relatively slow processor and low power batteries, and communicate over low bandwidth wireless communication links. Existing mutual exclusion algorithms for distributed systems are not suitable for mobile systems due to these limitations. We propose a look-ahead technique for distributed mutual exclusion which instead of enforcing mutual exclusion among all the sites of a mobile system, enforces mutual exclusion only among the sites which are concurrently competing for a critical section (CS), resulting in less message overhead. We refer to it as a look-ahead technique because it first looks to find out the sites that are currently requesting CS before sending out request messages. Designing look-ahead mutual exclusion involves two issues: identifying sites which are concurrently competing for CS; and enforcing mutual exclusion among these sites. We systematically develop a look-ahead mutual exclusion algorithm from the first principles, which suits mobile computing environments. Look-ahead mutual exclusion algorithms are more efficient because they eliminate unnecessary communication among sites. Message traffic is proportional to the average number of active sites at any time instead of the total number of sites in the system.