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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

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Roadmap

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  1. 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 Roadmap

  2. 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. 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. 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. 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. 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. Finally… • See http://www-course.cs.york.ac.uk/crt for course web page to help with exam preparation • 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

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