Mike Stephen Fulton

Design and implementation of a comprehensive real-time java virtual machine

The emergence of standards for programming real-time systems in Java has encouraged many developers to consider its use for systems previously only built using C, Ada, or assembly language. However, the RTSJ standard in isolation leaves many important problems unaddressed, and suffers from some serious problems in usability and safety. As a result, the use of Java for real-time programming has continued to be viewed as risky and adoption has been slow. In this paper we provide a description of IBMs new real-time Java virtual machine product, which combines Metronome real-time garbage collection, ahead-of-time compilation, and a complete implementation of the RTSJ standard, running on top of a custom real-time multiprocessor Linux kernel. We will describe the implementation of each of these components, including how they interacted both positively and negatively, and the extensions to previous work required to move it from research prototype to a system implementing the complete semantics of the Java language. The system has been adopted for hard real-time development of naval weapons systems and soft real-time telecommunications servers. We present measurements showing that the system is able to provide sub-millisecond worst-case garbage collection latencies, 50 microsecond Linux scheduling accuracy, and eliminate non-determinism due to JIT compilation.

Compilation Techniques for Real-Time Java Programs

In this paper, we introduce the IBMreg WebSpherereg real time product, which incorporates a virtual machine that is fully Javatrade compliant as well as compliant with the Real-Time Specification for Java (RTSJ). We describe IBMs real-time Java enhancements, particularly in the area of our Testarossa (TR) ahead-of-time (AOT) compiler, our TR just-in-time (JIT) compiler, and our Metronome (Bacon, et al., 2003) deterministic garbage collector (GC). The main focus of this paper is on the various techniques employed by the TR compilers to optimize and regulate the performance of code running in a real-time Java environment through a simple Java source code example. Through the example, we highlight the additional checks required to provide a conformant RTSJ implementation as well as the performance issues with ahead-of-time code generation and the overheads required to support Metronome. We show how these checks are implemented in a production JVM, and then report the cost of the real-time changes in practice for the example as well as the SPECjvm98 benchmark suite, SPECjbb2000, and SPECjbb2005