1. © Andy Wellings, 2004 Concurrent and Real-Time Programming in Java  Electronic copies of course foils available via  http://www-course.cs.york.ac.uk/crt  Course book: “ Concurrent and Real-Time Programming in Java ” Andy Wellings, Wiley, 2004 ( £ 20.99 from Amazon)  Real-Time Specification for Java (RTSJ) Versions 1.0.1 is available from  http://www.rtj.org

2. © Andy Wellings, 2004 Books RTSJ Version 0.9 RTSJ Version 1.0.1

3. © Andy Wellings, 2004 Other books RTSJ Version 0.9RTSJ Version 1.0

4. © Andy Wellings, 2004 Practicals  Start week 3  Demonstrators:

5. © Andy Wellings, 2004 Thursday 14.15

6. © Andy Wellings, 2004 Thursday 15.15

7. © Andy Wellings, 2004 Prerequisites  You should already:  be a competent programmer in an imperative programming language like C, Pascal, Ada, C++, C# etc  be able to program in sequential Java  have a good understanding of Operating System Principles, in particular the mechanisms needed to support concurrency, e.g. processes, semaphores, etc

8. © Andy Wellings, 2004 Overall Technical Aims of the Course  To understand the basic requirements of concurrent and real-time systems  To understand how these requirements have influenced the design of Java and the Real-Time Specification for Java  To be able to program advanced concurrent real-time Java systems

9. © Andy Wellings, 2004 Course Contents I  Introduction to Course, Concurrent and Real-Time Programming  Concurrent Programming in Java  Communication and Synchronization  Motivation for, and an overview of, the RTSJ  Memory Management  Clocks and Time  Scheduling and Schedulable Objects  Asynchronous Events and Handlers

10. © Andy Wellings, 2004 Course Contents II  Real-Time Threads  Asynchronous Transfer of Control  Resource Control  Schedulability Analysis  Conclusions

11. © Andy Wellings, 2004 Concurrent Programming  The name given to programming notation and techniques for expressing potential parallelism and solving the resulting synchronization and communication problems  Implementation of parallelism is a topic in computer systems (hardware and software) that is essentially independent of concurrent programming  Concurrent programming is important because it provides an abstract setting in which to study parallelism without getting bogged down in the implementation details

12. © Andy Wellings, 2004 Why we need it  To fully utilise the processor 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 10 2 1 -8 10 -9 Response time in seconds 10 0 humantape floppy CD memory processor

13. © Andy Wellings, 2004 Parallelism Between CPU and I/O Devices CPUI/O Device Initiate I/O Operation Process I/O Request Signal Completion Interrupt I/O Routine I/O Finished Continue with Outstanding Requests

14. © Andy Wellings, 2004 Why we need it  To allow the expression of potential parallelism so that more than one computer can be used to solve the problem  Consider trying to find the way through a maze

15. Sequential Maze Search

16. Concurrent Maze Search

17. © Andy Wellings, 2004 Why we need it  To model the parallelism in the real world  Virtually all real-time systems are inherently concurrent — devices operate in parallel in the real world  This is, perhaps, the main reason to use concurrency

18. Air Traffic Control

19. © Andy Wellings, 2004 Why we need it  Alternative: use sequential programming techniques  The programmer must construct the system as the cyclic execution of a program sequence to handle the various concurrent activities  This complicates the programmer's task and involves considerations of structures which are irrelevant to the control of the activities in hand  The resulting programs will be more obscure and inelegant  Decomposition of the problem is more complex  Parallel execution of the program on more than one processor is more difficult to achieve  The placement of code to deal with faults is more problematic

20. © Andy Wellings, 2004 Terminology  A concurrent program is a collection of autonomous sequential processes, executing (logically) in parallel  Each process has a single thread of control  The actual implementation (i.e. execution) of a collection of processes usually takes one of three forms. Multiprogramming  processes multiplex their executions on a single processor Multiprocessing  processes multiplex their executions on a multiprocessor system where there is access to shared memory Distributed Processing  processes multiplex their executions on several processors which do not share memory

21. © Andy Wellings, 2004 What is a real-time system?  A real-time system is any information processing system which has to respond to externally generated input stimuli within a finite and specified period  the correctness depends not only on the logical result but also the time it was delivered  failure to respond is as bad as the wrong response!  The computer is a component in a larger engineering system => EMBEDDED COMPUTER SYSTEM  99% of all processors are for the embedded systems market

22. © Andy Wellings, 2004 Terminology  Hard real-time — systems where it is absolutely imperative that responses occur within the required deadline. E.g. Flight control systems.  Soft real-time — systems where deadlines are important but which will still function correctly if deadlines are occasionally missed. E.g. Data acquisition system.  Firm real-time — systems which are soft real-time but in which there is no benefit from late delivery of service. A system may have all hard, soft and real real-time subsystems Many systems may have a cost function associated with missing each deadline

23. © Andy Wellings, 2004 A simple fluid control system Pipe Flow meter Valve Interface Computer Time Input flow reading Processing Output valve angle

24. © Andy Wellings, 2004 A Grain-Roasting Plant Fuel Tank Furnace Bin Pipe fuel grain

25. © Andy Wellings, 2004 A Process Control System Process Control Computer Chemicals and Materials Valve Temperature Transducer Stirrer Finished Products PLANT

26. © Andy Wellings, 2004 A Production Control System Production Control System Parts Machine ToolsManipulatorsConveyor Belt Finished Products

27. © Andy Wellings, 2004 A Command and Control System Temperature, Pressure, Power and so on Terminals Command and Control Computer Command Post Sensors/Actuators

28. © Andy Wellings, 2004 A Typical Embedded System Algorithms for Digital Control Data Logging Data Retrieval and Display Operator Interface Engineering System Remote Monitoring System Real-Time Clock Database Operator’s Console Display Devices Real-Time Computer

29. © Andy Wellings, 2004 Characteristics of a RTS  Large and complex — vary from a few hundred lines of assembler or C to 20 million lines of Ada estimated for the Space Station Freedom  Concurrent control of separate system components — devices operate in parallel in the real-world; better to model this parallelism by concurrent entities in the program  Facilities to interact with special purpose hardware — need to be able to program devices in a reliable and abstract way

30. © Andy Wellings, 2004 Characteristics of a RTS  Extreme reliability and safe — embedded systems typically control the environment in which they operate; failure to control can result in loss of life, damage to environment or economic loss  Guaranteed response times — we need to be able to predict with confidence the worst case response times for systems; efficiency is important but predictability is essential

31. © Andy Wellings, 2004 Real-time Programming Languages  Assembly languages  Sequential systems implementation languages — e.g. RTL/2, Coral 66, Jovial, C.  Both normally require operating system support.  High-level concurrent languages. Impetus from the software crisis. e.g. Ada, Chill, Modula-2, Mesa, Java.  No operating system support!  We will focus on Java and the Real-Time Specification for Java  See Burns, Wellings, Real-Time Systems and Programming Languages, 3rd Edition, 2001, Addison Wesley for a general discussion on other languages and operating systems

32. © Andy Wellings, 2004 Java Architecture Real-time Operating System JVM JBC Standalone JVM JBC Hardware JVM JBC

33. © Andy Wellings, 2004 Summary I  The motivations for concurrent programming have been presented:  fully utilize the processor  allow parallel execution  model real world parallelism  Two main classes of real-time systems have been identified:  hard real-time systems  soft real-time systems

34. © Andy Wellings, 2004 Summary II  The basic characteristics of a real-time or embedded computer system are:  largeness and complexity,  manipulation of real numbers,  extreme reliability and safety,  concurrent control of separate system components,  real-time control,  interaction with hardware interfaces,  efficient implementation.

35. © Andy Wellings, 2004 Further Reading  Chapter 1 of Burns and Wellings, “ Real-Time Systems and Programming Languages ”, 3rd Edition, 2001 (in library)