Achieving submillisecond response times in a managed language environment such as Java or C# requires overcoming significant challenges. In this article, we propose Reflexes, a programming model and runtime system infrastructure that lets developers seamlessly mix highly responsive tasks and timing-oblivious Java applications. Thus enabling gradual addition of real-time features, to a non-real-time application without having to resort to recoding the real-time parts in a different language such as C or Ada. Experiments with the Reflex prototype implementation show that it is possible to run a real-time task with a period of 45 μs with an accuracy of 99.996% (only 0.001% worse than the corresponding C implementation) in the presence of garbage collection and heavy load ordinary Java threads.

The disadvantages of unconstrained shared-memory multi-threading in Java, especially with regard to latency and determinism in realtime systems, have given rise to a variety of language extensions that place restrictions on how threads allocate, share, and communicate memory, leading to order-of-magnitude reductions in latency and jitter. However, each model makes different trade-offs with respect to expressiveness, efficiency, enforcement, and latency, and no one model is best for all applications.

The stream programming paradigm aims to expose coarsegrained parallelism in applications that must process continuous sequences of events.The appeal of stream programming comes from its conceptual simplicity.A program is a collection of independent filters which communicate by the means of uni-directional data channels.This model lends itself naturally to concurrent and efficient implementations on modern multiprocessors.As the output behavior of filters is determined by the state of their input channels, stream programs have fewer opportunities for the errors (such as data races and deadlocks) that plague shared memory concurrent programming.This paper introduces STREAMFLEX, an extension to Java which marries streams with objects and thus enables to combine, in the same Java virtual machine, stream processing code with traditional object-oriented components.STREAMFLEX targets high-throughput low-latency applications with stringent quality-of-service requirements.To achieve these goals, it must, at the same time, extend and restrict Java.To allow for program optimization and provide latency guarantees, the STREAMFLEX compiler restricts Java by imposing a stricter typing discipline on filters.On the other hand, STREAMFLEX extends the Java virtual machine with real-time capabilities, transactional memory and type-safe region-based allocation.The result is a rich and expressive language that can be implemented efficiently.

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 running at 22.05KHz. The number of missed deadlines, less than 0.2% for 10 million observations, compares favorably to a native C implementation.