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. In this paper we present Flexible Task Graphs (Flexotasks), a single system that allows different isolation policies and mechanisms to be combined in an orthogonal manner, subsuming four previously proposed models as well as making it possible to use new combinations best suited to the needs of particular applications. We evaluate our implementation on top of the IBM Web-Sphere Real Time Java virtual machine using both a microbenchmark and a 30 KLOC avionics collision detector. We show that Flexotasks are capable of executing periodic threads at 10 KHz with a standard deviation of 1.2µs and that it achieves significantly better performance than RTSJ’s scoped memory constructs while remaining impervious to interference from global garbage collection.

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

The automotive industry has recent ambitions to integrate multiple applications from different micro controllers on a single, more powerful micro controller. The outcome of this integration process is the loss of the physical isolation and a more complex monolithic software. Memory protection mechanisms need to be provided that allow for a safe co-existence of heterogeneous software from different vendors on the same hardware, in order to prevent the spreading of an error to the other applications on the controller and leaving an unclear responsibility situation. With our prototype system KESO, we present a Java-based solution for robust and safe embedded real-time systems that does not require any hardware protection mechanisms. Based on an OSEK/VDX operating system, we offer a familiar system creation process to developers of embedded software and also provide the key benefits of Java to the embedded world. To the best of our knowledge, we present the first Multi-JVM for OSEK/VDX operating systems. We report on our experiences in integrating Java and an embedded operating system with focus on the footprint and the real-time capabilities of the system.

While managed languages such as C # and Java have become quite popular in enterprise computing, they are still considered unsuitable for hard real-time systems. In particular, the presence of garbage collection has been a sore point for their acceptance for low-level system programming tasks. Realtime extensions to these languages have the dubious distinction of, at the same time, eschewing the benefits of highlevel programming and failing to offer competitive performance. The goal of our research is to explore the limitations of high-level managed languages for real-time systems programming. To this end we target a real-world embedded platform, the LEON3 architecture running the RTEMS real-time operating system, and demonstrate the feasibility of writing garbage collected code in critical parts of embedded systems. We show that Java with a concurrent, real-time garbage collector, can have throughput close to that of C programs and comes within 10 % in the worst observed case on realistic benchmark. We provide a detailed breakdown of the costs of Java features and their execution times and compare to real-time and throughput-optimized commercial Java virtual machines.

anderen Hochschule eingereicht und hat noch keinen sonstigen Prüfungszwecken gedient. Marburg, denAcknowledgments I would like to acknowledge the help of several people during the course of this doctoral thesis. First of all, I would like to thank my thesis supervisor Prof. Dr. Bernd Freisleben for his permanent support during the course of this thesis. I would also like to thank Prof. Dr. Helmut Dohmann for numerous inspiring discussions about the subject of this thesis. My thank also goes to the TiCS development team for helping to implement, test, and improve the framework: Christoph Stoidner, Roland Schwarzkopf, Steffen Heinzl, Tim Dörnemann, and Jochen Gärtner.