Themis: Enforcing Titanium Consistency on the NOW

Titanium is a single program, multiple data (SPMD) programming language based on Java. Titanium defines a data consistency model equivalent to the Java specification. This consistency model calls for locally sequential consistency, with global consistency attained at synchronization points and arbitrary write reordering. The Titanium language is targeted at homogeneous multiprocessors on distributed memory architectures. Accesses to distant memory locations may result in communication over a network. The Themis system builds a Titaniumcompliant consistency interface for Active Messages running on a NOW. This paper examines several methods for designing a Themis system that performs well for Titanium applications. Microbenchmark tests and a Conjugate Gradient Method test show the viability of each of these designs. One of the methods, a caching mechanism called OrderCache, displays promise for reducing communication loads and exploiting the locality of data within applications.