Expedited Real-Time Task Graphs (XRTGs) are a way to program real-time applications in a slightly restricted subset of Java™ in order to achieve time portability and low scheduling latency. XRTGs are substantially less restrictive than both the NoHeapRealtimeThread construct of the Real Time Specification for Java (RTSJ) and the precursor technology Expedited Realtime Threads, posted here on alphaWorks last year.

This technology runs on Linux®, but development can be done on any platform that supports Java 5.0 and Eclipse.

How does it work?

A program is developed as a set of tasks (called "exotasks") that communicate via channels. Eclipse-based tools help with initial application structuring. The developer assigns time offsets within a real-time period to only those tasks that have explicit timing requirements. A scheduler ensures that the resulting program runs with the same timing on all platforms with sufficient resources.

Exotasks have private heaps so that they can allocate objects freely and have them collected as garbage. However, exotask heaps are collected at times determined by the scheduler, and the garbage collector for the global heap does not interfere with exotask execution.

Joshua Auerbach, Ph.D., wrote the XRTG implementation. In 24 years at IBM, Dr. Auerbach has contributed to many products, including IBM® WebSphere® Real Time and IBM WebSphere Messaging. His research contributions have been in communications, distributed systems, and programming languages.

David F. Bacon, Ph.D., is a research staff member at IBM""s T. J. Watson Research Center. There he leads the Metronome project, which produced the first hard real-time, garbage-collected system. His algorithms are included in most compilers and run-time systems for modern object-oriented languages. Dr. Bacon holds six patents, is a member of ACM and IEEE, and is on the governing boards of ACM SIGPLAN and SIGBED.

Christoph M. Kirsch, Dr.Ing., is currently a full professor at the University of Salzburg. He co-invented the Giotto and HTL languages that served as inspiration for XRTGs. Dr. Kirsch leads the JAviator unmanned-aerial-vehicle project for which he recently received an IBM faculty award. He is a member of the ACM and IEEE, co-founded the ACM/SIGBED International onference on Embedded Software (EMSOFT), and is chairing the Embedded Systems Week (ESWEEK) Organizing Committee in 2007.