Ownership types provide a statically enforceable notion of object-level encapsulation. We extend ownership types with computational e#ects to support reasoning about objectoriented programs. The ensuing system provides both access control and e#ects reporting. Based on this type system, we codify two formal systems for reasoning about aliasing and the disjointness of computational e#ects. The first can be used to prove that evaluation of two expressions will never lead to aliases, while the latter can be used to show the non-interference of two expressions.

The Multitasking Virtual Machine (called from now on simply MVM) is a modification of the Java ™ virtual machine. It enables safe, secure, and scalable multitasking. Safety is achieved by strict isolation of applications from one another. Resource control mechanisms augment security by preventing some denial-ofservice attacks. Improved scalability results from an aggressive application of the main design principle of MVM: share as much of the runtime as possible among applications and replicate everything else. The system can be described as a ‘no compromise ’ approach – all the known APIs and mechanisms of the Java programming language are available to applications. MVM is implemented as a series of carefully tuned modifications to the Java HotSpot ™ virtual machine, including the dynamic compiler. This paper presents the design of MVM, focusing on several novel and general techniques: an in-runtime design of lightweight isolation, an extension of a copying, generational garbage collector to provide best-effort management of a portion of the heap space, and a transparent and automated mechanism for safe execution of user-level native code. MVM demonstrates that multitasking in a safe language can be accomplished with a high degree of protection, without constraining the language, and with competitive performance characteristics.

Abstract. The success of Java in recent years is largely due to its targeting as a language for the Internet. Many of the network-related features of Java however are not part of the core language design. In this paper we focus on the design of a more parsimonious Internet programming language, which supports network integration smoothly and coherently as part of its core specification. The key idea is to center these extensions around the unified notion of a cell. Cells are deployable containers of objects and code, which may import (plugin) and export (plugout) classes and operations. They may be dynamically linked and unlinked, locally or across the network. Cells may be dynamically loaded, unloaded, copied, and moved, and serve as units of security. At first approximation, cells can be thought of as a hybrid between modules and components. Here we concentrate on the design of JCells, a language which builds cells on top of the fundamental Java notions of class, object, and virtual machine. 1