John R. Rose

Fast subtype checking in the HotSpot JVM

We present the fast subtype checking implemented in Suns HotSpot JVM. Subtype checks occur when a program wishes to know if class S implements class T, where S and T are not both known at compile-time. Large Java programs will make millions or even billions of such checks, hence a fast check is essential. In actual benchmark runs our technique performs complete subtype checks in 3 instructions (and only 1 memory reference) essentially all the time. In rare instances it reverts to a slower array scan. Memory usage is moderate (11 words per class) and can be traded off for time. Class loading does not require recomputing any data structures associated with subtype checking.

Integrating the Scheme and C languages

Most implementations of Scheme (and other Lisp dialects) provide some facility for calling functions defined in ANSI C (or other popular languages) even if only to implement Scheme’s primitive operations. Some relatively sophisticated implementations provide access to non-Scheme data structures, Taking a Scheme-centered view, we will refer to these facilities as~oreign call-out, for both data and functions access. Scheme implementations may also provide ways for C code to use Scheme functions and data structures more or less directly. We will refer to this as~oreign call-in.

The use of multimethods and method combination in a CLOS based window interface

Solo is a portable window interface written in the Common Lisp Object System (CLOS) object-oriented programming language. Solo provides a virtual window machine which is targeted to a host window system by implementing a set of host window system specific classes and methods for Solos host window system driver protocol. The interface presented by Solo to an application insulates it from differences in the host window system, facilitating application portability. Solo distinguishes itself from other object-oriented window systems by exploiting certain features of CLOS. CLOS method combination simplifies initialization of windows while preserving easy extensibility of the basic classes. Generic dispatch on multiple arguments, a feature unique to CLOS, allows a simpler and more flexible input event dispatching protocol. A powerful event description language simplifies the specification of keyboard and mouse events. A prototype implementation runs on the server based XII and NeWS host systems, and on the frame buffer based Lucid Window Toolkit.

Refined types: highly differentiated type systems and their use in the design of intermediate languages

The choices made in the design of a compiler’s Intermediate Language (abbreviated in this paper by IL) strongly affect that compiler’s simplicity, robustness, and flexibility. In this paper, we briefly discuss how an IL bridges the gap between a high-level source language (abbreviated SL) to a low-level target language (abbreviated TL) by a process called lowering, which is the simple process of translation apart from any optimization. We then observe that lowering is particularly reliable and simple if mediated by a type system that provides for the construction of abstract data types.