Virtual Machines

I love virtual machines (VMs) and I have done for a long time.If that makes me "sad" or an "anorak", so be it. I love them because they are so much fun, as well as being so useful. They have an element of original sin (writing assembly programs and being in control of an entire machine), while still being able to claim that one is being a respectable member of the community (being structured, modular, high-level, object-oriented, and so on). They also allow one to design machines of one's own, unencumbered by the restrictions of a starts optimising it for some physical particular processor (at least, until one processor or other). I have been building virtual machines, on and off, since 1980 or there­ abouts. It has always been something of a hobby for me; it has also turned out to be a technique of great power and applicability. I hope to continue working on them, perhaps on some of the ideas outlined in the last chapter (I certainly want to do some more work with register-based VMs and concur­ rency). I originally wanted to write the book from a purely semantic viewpoint.

Virtual Machines offers a unique insight into the building of virtual machines for sequential, object-oriented and parallel languages, and uses comparisons of different VMs to provide actual, practical examples on how to build VMs.

State transitions are used as a formal technique for the specification of virtual machines throughout and - in addition – transitions and state transitions relating to the general operation are included for specification of the virtual machine for the event-based system. Two virtual machines are defined using a simple sequential language, which is then generalised to include object and parallelism. Other themes explored include the implementation of VMs and proposals for future work. Appendices contain high-level specifications of two compilers: one for the simple language that serves as the basic example throughout the book, the other for the event-based language specified in Chapter 6.

This book is an essential reference tool for academic and industrial researchers as well as postgraduates in this area.