A portable real-time extension set for Java

Since the fourth quarter of 1999, the authors engaged in a project where Java was employed to build the real-time control program inside a plastic-injection-molding machine. However, at that time, since the official real-time Java standard-the Real-Time Specification for Java (RTSJ) from the Sun Microsystems was still under development, no RTSJ-compliant Java virtual machine was available. To satisfy our requirement, we designed and implemented a real-time extension library for enhancing the Java virtual machine that was already available in the real-time operating system we used. Our extension library has the following advantages: First, the underlying Java virtual machine needs no modification to accommodate it. Second, this extension library is easy to be ported to any other priority-based real-time operating systems. Third, the core of this extension library is basically derived from the subset of the RTSJ public draft, and thus our real-time control program can be move to a forthcoming RTSJ-compliant Java virtual machine without much difficulty. In brief, our work may help suggest ways of implementing RTSJ, or the notion of (degrees of) "minimal" compliance/support of RTSJ based on non-RTSJ Java virtual machines. In this paper, we show the requirement, application programming interface, and implementation of this extension library, and discuss its influence on timing.