Exploring real-time features of Java']Java VM

Object oriented software design is getting more and more common in the field of industrial control. In particular, Java seems extremely versatile for the development of distributed control applications. One of the main requirements of control application is a deterministic execution of the tasks, which generally feature real-time constraints. When Java language has been conceived, a little weight to the real-time requirements of applications has been given. In the last few years the limits to the use of Java for Real-Time applications has led to the definition of Java Real-Time platform specifications. Real-Time capability of a Java Virtual Machine (VM) depends on a very large number of elements, among which the task scheduling algorithm, the memory management, the garbage collector algorithm and its execution policy. Knowledge of how each single internal mechanism of a Java VM influence its performance is very important to improve its real-time behaviour. This paper must be considered as a first step toward this direction, as its aim is to try to understand how real-time performance of a Java VM may be influenced by each its single component.