John N. Zigman

Reducing data communication overhead for DOACROSS loop nests

If the iterations of a loop nest cannot be partitioned into independent tasks, data communication for data dependence is inevitable in order to execute them on parallel machines. This kind of loop nest is referred to as a DOACROSS loop nest. This paper is concerned with compiler algorithms for parallelizing DOACROSS loop nests for distributed-memory multicomputers. We present a method that combines loop tiling, chain-based scheduling and indirect message passing to generate efficient message-passing parallel code. We present our experiment results on the Fujitsu AP1000 to show that low communication overhead and high speedup for DOACROSS loop nests on multicomputers can be achieved by tuning these techniques.

Starting with termination: a methodology for building distributed garbage collection algorithms

We propose an effective methodology in which a distributed garbage collector may be derived from a distributed termination algorithm and a centralized garbage collector in a manner that preserves interesting properties of the original collector, such as completeness. To illustrate our technique, we show how two distributed termination algorithms, credit recovery and task balancing, may be suitably described; and then map four centralized garbage collectors: reference counting; mark/scan; a generational scheme; and the Mature Object Space collector (MOS) onto this description. The advantage of our approach is that by separating the issues of distribution and collection, we alleviate the difficulty of inventing, understanding, and comparing distributed garbage collection techniques.

Fast portable orthogonally persistent Java

SUMMARY A powerful feature of the Java programming language is its user-definable class loading policy, which when combined with the namespace independence between class loaders, allows portable implementation of semi-dynamic program transformations. Such transformations can be used for a range of purposes, including optimization and semantic extension. In this paper we present a framework for semantic extensions in Java. This framework consists of a number of simple but powerful transformations that, among other things, allow us to semantically extend Java to provide orthogonal persistence. The use of semi-dynamic program transformations lends our orthogonally persistent Java a number of important qualities, including simplicity, portability and a clean model of persistence. Significantly , our implementations are efficient and can outperform in some cases PJama , a well-known orthogonally persistent Java, which is based on a modified virtual machine. In addition to describing the application of these transformations to orthogonally persistent Java, we foreshadow their use in a number of other contexts, including dynamic instance versioning and instrumentation. Copyright c 1999 John Wiley & Sons, Ltd.

Implementing Orthogonally Persistent Java

Orthogonally persistent Java combines the power of abstraction over persistence with Javas rich programming environment. In this paper we report our experience in designing and implementing orthogonally persistent Java. Our design approach is anchored by the view that any system that brings together Java and orthogonal persistence should as far as possible avoid diluting the strengths of Java or the principles of orthogonal persistence. Our approach is thus distinguished by three features: complete transparency of persistence, support for both intra and inter application concurrency throughACID transactions, and the preservation of Javas property of portability. In addition to discussing design and implementation, we present results that show that our approach performs credibly.