Multiple Subtyping in a Persistent Distributed Shared Memory Operating System

摘要

Plurix is an object-oriented Operating System (OS) developed for the PC platform. Network communication is implemented via Distributed Shared Memory (DSM) management using restartable transactions and optimistic synchronization. The OS is developed with a proprietary Java compiler transforming Java sources into Intel protected mode code. Abandoning the hardware independence of Java eliminates loss of performance and allows developing the total OS in Java. In this paper we focus on Java interfaces offering multiple subtyping in the Plurix OS but our approach is applicable to any other strong typing object-oriented language. After a short review of the Plurix environment we present how Java interfaces are realized efficiently with respect to method dispatch overhead. We show how the Java typing rules are realized using pseudo sub-typing. Furthermore we reveal interesting semantic amiguities of interface reference members arising in a persistent DSM. We suggest extended initialization rules to overcome these problems. In this context we also introduce meta interface descriptors together with a generalized type equivalence check scheme.