Real-time Java Virtual Machine Research

Many of the advantages of Java, such as safe object references, the notion of concurrency as a first-class language construct, and its portability, have the potential to make embedded systems much safer and simpler to program. With the advantages mentioned above, Java is increasingly expected to become the leading programming language in embedded systems.Java technology is seldom used in real-time systems currently, due to the lack of acceptable real-time performance. To improve the real-time performance specified in the Java Language Specification and the Java Virtual Machine Specification, Greg Bollella et al propose the Real-Time Specification for Java (RTSJ). It provides a guideline for the implementation of real-time Java platform.The main research content of this paper is how to improve the traditional Java virtual machine, and make it to overcome the adverse effect to the real-time system from the late analyzes. In this paper, we implement a method, this method can check out the classes and methods of real-time from the constant pool. This method can provide the fully qualified name of the types and methods. Through these names we can locate these classes and methods and then deal with them in advance. The advantage of this method is that it will not change the Java compiler and will not change the API identified in the RTSJ. The programmers only need to write traditional Java programs which can support for the real-time tasks. Related processing for the real time will be done by the Java virtual machine automaticly.After get these classes and methods which need to be deal with in advance, this paper introduce a method how to get them ready before the processing of the program. The main implementation is loading, linking and initialization the classes which are relevant of real time, then analysis the byte codes in the methods. From this method the Java virtual machine can avoid the adverse effects which are caused by late loading and late analyzing. The system can run the byte codes which have been analyzed and use the analyzed constant pool entrance. At last this paper implements Inline-threading dispatching technology by pre-analyzing the byte codes. This can prove that some useful advance preparation to the critical byte codes can improve the efficiency of the program execution.