Coherency of Shared Memory in Ad-Hoc Networks

Memory coherence is a commonly accepted correctness criterion for distributed shared-memory computing platforms. Coherence is formulated assuming a static architecture in which all processors can communicate with one another. In this paper, we argue that the classical notion is not appropriate for ad-hoc networks consisting of mobile devices with constantly changing communication topology. We introduce and formalize a new correctness criterion, called group coherence, as a suitable abstract specification for shared-memory computing architectures over ad-hoc networks. We show that two existing systems, the Coda file system and Lampson’s global naming scheme, satisfy our definition. Finally, we propose a timestamp-based extension of the popular Snoopy cache coherence protocol for caching in ad-hoc networks, and show it to be group coherent.