A Multi-copy Distributed Shared Memory

Abstract

This chapter presents a “multi-copy” version of the single-copy distributed shared memory implementation given in Chap. 18. The multi-copy version maintains, for each page, one write copy and zero or more read-only copies. All the copies have the same value. Each copy is with a different component system. The write copy is accompanied by a so-called copyset, which is the set of addresses of component sytems that have read-only copies. A component system can read from the write copy or a read-only copy. It can write to the write copy only, and that too only when there are no read-only copies anywhere. When a component system attempts to read or write a page that is not locally present, it acquires the write copy of the page, leaving a read copy at the previous location of the write copy. The component system can then read from the page. To write to the page, the component system informs all component systems in the page’s copyset to “invalidate” (i.e., delete) their copies, after which it can update its (write) copy [1].