1. © Andy Wellings, 2003 Roadmap  Introduction  Concurrent Programming  Communication and Synchronization  Completing the Java Model  Overview of the RTSJ  Memory Management  Clocks and Time  Scheduling and Schedulable Objects  Asynchronous Events and Handlers  Real-Time Threads  Asynchronous Transfer of Control  Resource Control  Schedulability Analysis  Conclusions

2. © Andy Wellings, 2003 Conclusions  Java has been generally immensely successful, however, it has yet to establish itself in the real-time and embedded markets  The provision of real-time programming abstractions along with the promise of a predictable real-time Java Virtual Machine has the potential give Java a foothold  However, there are still obstacles to be overcome; the main challenges are:  Specification — to produce a consistent and unambiguous Real-Time Specification for Java along with well-defined profiles for particular real- time application domains  Implementation — to generate efficient implementations of real-time virtual machines (both open source and propriety ones) for the full specification and the profiles  Maintaining Momentum — to stimulate evolution of the specification in a controlled and sustained manner to add new functionality and to address new architectures

3. © Andy Wellings, 2003 Specification Challenges I  Schedulable objects  The RTSJ generalize real-time activities away from real-time threads towards the notion of schedulable objects ( real-time threads and asynchronous event handlers)  Unfortunately, the operations that can be performed on a schedulable object are not consistently defined  E.g. a schedulable object can create and enter into one or more scoped memory areas; the methods for manipulating the resulting scoped memory stack can be found partly in RealtimeThread and partly in AsyncEventHandler  Ideally, all operations associated with schedulable object should be defined either in the Schedulable interface or in the class defining the associated functionality (in this case the MemoryArea class)

4. © Andy Wellings, 2003 Specification Challenges II  Aperiodic and sporadic real-time threads  AperiodicParameters and SporadicParameters can only successfully be used with asynchronous event handlers  There is no notion of a release event for an aperiodic (or sporadic) thread and consequently it is difficult to see how an implementation can detect deadline miss or cost overrun  The WaitForNextPeriod method  Is only applicable to real-time threads with periodic release parameters  Ideally, RealtimeThread should contain a waitForNextRelease method rather than a waitForNextPeriod method.  A releaseRealtimeThread method would also be needed  This approach would also solve the previous problem with aperiodic threads, and provide a level of consistency between asynchronous event handlers and real-time threads

5. © Andy Wellings, 2003 Implementation Challenges  Memory management  The new memory management assignment rules must be checked by an implementation  Whilst it is clear that static analysis of programs can eliminate many of the run-time checks, this requires special RTSJ-aware compilers or tools.  The availability of these, along with efficient run-time implementations of the overall model, may well determine the eventual impact and take up of the RTSJ  Asynchronous Transfer of Control  It a major challenge to keep the ATC overheads in the JVM small and predictable, and to ensure that code not using this facility suffers minimal impact

6. © Andy Wellings, 2003 Maintaining Momentum  With any new technology, there is a tension between producing a stable standard base which users can depend on, and providing a dynamic product that continues to evolve and address new application needs  Java has caught the imagination of the user-community, produced stable releases and maintained momentum for its evolution.  If the RTSJ is to survive, it is important that it keeps pace with the more general Java development and also that it develops its own momentum.  New standard schedulers  Multiple schedulers  Multiple criticalities  Alternative interrupt handling models  Real-time concurrency utilities  Multiprocessor and distributed systems

7. © Andy Wellings, 2003 Finally …  See http://www-course.cs.york.ac.uk/crt for course web page to help with exam preparationhttp://www-course.cs.york.ac.uk/crt  The exam will consist of three questions of which you have to answer two. You will be given summaries of all Java classes/interfaces used in the course  One question will be on concurrent programming in Java, the other two will be on the RTSJ  Typically a question has  a general part asking you to explain some concept (bookwork)  an unseen analysis or problem part, for example sketch some code to solve a particular problem or illustrate an algorithm analysis of a situation - e.g given some code with ATC components what happen when the ATC is fired illustrate the execution of some particular threads which use priority inheritance, or scoped memory