Virtual machines (vms) have enjoyed a resurgence as a way of allowing the same application program to be used across a range of computer systems. This flexibility comes from the abstraction that the vm provides over the native interface of a particular computer. However, this also means that the application is prevented from taking the features of particular physical machines into account in its implementation. This dissertation addresses the question of why, where and how it is useful, possible and practicable to provide an application with access to lower-level interfaces. It argues that many aspects of vm implementation can be devolved safely to untrusted applications and demonstrates this through a prototype which allows control over run-time compilation, object placement within the heap and thread scheduling. The proposed architecture separates these application-specific policy implementations from the application itself. This allows one application to be used with different policies on different systems and also allows nave or premature optimizations to be removed.

This paper examines the compression of source code, the original high-level language representation of a program. We discuss the results (both advantages and disadvantages) of this choice in more detail in later sections, but two intuitive reasons for supposing compressed source code results in the smallest program representation are worth mentioning at this point.

OpenJIT is an open-ended, reflective JIT compiler framework for Java being researched and developed in a joint project by Tokyo Inst. Tech. and Fujitsu Ltd. Although in general self-descriptive systems have been studied in various contexts such as reflection and interpreter/compiler bootstrapping, OpenJIT is a first system we know to date that offers a stable, full-fledged Java JIT compiler that plugs into existing monolithic JVMs, and offer competitive performance to JITs typically written in C or C . We propose an architecture for a reflective JIT compiler on a monolithic VM, and describe the details of its frontend system. And we demonstrate how reflective JITs could be useful class- or application specific customization and optimization by providing an important reflective "hook" into a Java system.

Recently, there has been a rapidly expanding body of work with the vision of seamlessly integrating idle networked computers into virtual computing environments. This is enabled primarily by the success of research eorts promoting parallel and distributed computing on networks of workstations and the wide acceptance of Java. The proliferation of work in this area has provided new Internet-based infrastructures that harness the power of computing bases comprising hundreds of loosely-connected volunteered machines (i.e., hosts). While many of these systems have proposed the use of non-altruistic market-based schemes for promoting large-scale participation, mechanisms for ensuring that hosts participating in collaborative computing environments perform the work assigned to them have been largely ignored. This paper presents our implementation of one framework that layers a remote audit mechanism on top of an existing distributed computing model, and provides ecient methods for verifying,...