Multicast-based Runtime System for Highly Eecient Causally Consistent Software-only Dsm

This paper introduces the application of IP multicasting for enhancing of software-only DSM systems and, at the same time, sim-pliication of the programming model by ooering a simple memory consistency model. The described algorithm is the foundation of a runtime system implemented as lesystems for the Windows NT and FreeBSD operating systems. 1 Introduction Software distributed shared memory (DSM) realized on a network of workstations connected through a conventional computer network has gained a lot of attention in both research and industry. On the other hand group communication , also known as multicasting, on IP networks is getting widespread over the Internet. The new IP generation, IPv6, relies heavily on the availability of multicasting. This paper presents the idea of an application of IP multicasting for the purpose of coherence traac in software DSMs. 2 Related Work Speight and Bennett reported in 5] about the use of multicasting in the Brazos project. There main diierences between the Brazos approach and ours are the following: 1. DSM in Brazos is concentrated on scope consistency, that means a memory consistency model using synchronization variables; our approach is to provide causal consistent DSM. 2. Brazos relies implicitly on reliable multicast, whereas we do not. The Orca distributed system 1] uses totally ordered group communication for a MRMW write-update coherence protocol. The protocol employs a centralized component-the sequencer-to achieve totally ordered multicast on top of the potentially unreliable IP multicast. In our design this centralized component is avoided.