Commercial Java virtual machines are designed to maximize the performance of applications at the expense of predictability. High throughput garbage collection algorithms, for example, can introduce pauses of 100 milliseconds or more. We are interested in supporting applications with response times in the tens of microseconds and their integration with larger timing-oblivious applications in the same Java virtual machine. We propose Reflexes, a new abstraction for writing highly responsive systems in Java and investigate the virtual machine support needed to add Reflexes to a Java environment. Our implementation of Reflexes was evaluated on several programs including an audio-processing application. We were able to run a Reflex at 22.05KHz with less than 0.2 % missed deadlines over 10 million observations, a result that compares favorably to an implementation written in C.

Implementing a concurrent programming language such as Java by the means of a translator to an existing language is attractive as it provides portability over all platforms supported by the host language and reduces development time – as many low-level tasks can be delegated to the host compiler. The C and C++ programming languages are popular choices for many language implementations due to the availability of efficient compilers on a wide range of platforms. For garbage-collected languages, however, they are not a perfect match as no support is provided for accurately discovering pointers to heap-allocated data on thread stacks. We evaluate several previously published techniques, and propose a new mechanism, lazy pointer stacks, for performing accurate garbage collection in such uncooperative environments. We implemented the new technique in the Ovm Java virtual machine with our own Java-to-C/C++ compiler using GCC as a back-end compiler. Our extensive experimental results confirm that lazy pointer stacks outperform existing approaches: we provide a speed-up of 4.5 % over Henderson’s accurate collector with a 17 % increase in code size. Accurate collection is essential in the context of real-time systems, we thus validate our approach with the implementation of a real-time concurrent garbage collection algorithm. 1.

The Real-time Specification for Java extends the Java platform