PLaVa: a lightweight persistent Java virtual machine

Abstract

This paper describes the implementation and tuning of an orthogonally persistent Java Virtual Machine (JVM) for small computers. It is based on a JVM that was targeted at a digital satellite television decoder with 1 megabyte each of ROM and RAM. Orthogonally persistent languages allow all program values to persist on disk, regardless of their type; and enable program code to have the same form regardless of the longevity of the data on which it operates. They improve productivity because there is no need for programmers to learn a separate database language or to manage data transfer and translation when using persistent objects. Java has received a lot of attention since its release by Sun Microsystems in 1995. Many fea­tures of Java make it well suited to orthogonal persistence: source code is compiled to a platform independent bytecode; there is implicit heap management, strong typing and useful programming constructs like threads, exceptions and classes. Java is also appropriate for embedded applications because of its safety and security features. Several researchers have now begun working on persistent Java implementations. This paper demonstrates the feasibility of accessing a persistent Java store from very small computers which obtain applets over the net. The paper starts with an overview of persistent systems, followed by an explanation of how the Java language itself has been affected by the addition of persistence. The next section discusses how the support for persistence has been added to the virtual machine. That is followed by a section discussing related work and we conclude with long-term goals.