JAVA-BASED REAL-TIME PROGRAMMING

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4. Exercises and Labs /** * The buffer. */ class Buffer { Semaphore mutex; // For mutual exclusion blocking. Semaphore free; // For buffer full blocking. Semaphore avail; // For blocking when no data is available. String buffData; // The actual buffer. } Buffer() { mutex = new MutexSem(); free = new CountingSem (1); avail = new CountingSem (); } void putLine(String input) { free.take(); // Wait for buffer empty. mutex.take(); // Wait for exclusive access. buffData = new String(input); // Store copy of object. mutex.give(); // Allow others to access. avail.give(); // Allow others to get line. } String getLine() { // Exercise 2 ... // Here you should add code so that if the buffer is empty, the // calling process is delayed until a line becomes available. // A caller of putLine hanging on buffer full should be released. // ... } 102 2012-08-29 16:05
4.2 Exercise 2 – Lab 1 preparation 4.2. Exercise 2 – Lab 1 preparation In this exercise you will design a real-time system for an alarm clock application using threads, semaphores and provided hardware interfaces. In lab 1 you will implement your design (the implementation usually takes longer than two hours so be sure to start well in advance of the lab occasion). Study the provided specification, description of the handout code and hardware emulator and answer the following questions (express your design in class diagrams and Java code where necessary): 1. What parallel activities are needed, i.e., which thread objects do you need? 2. What common data need to be shared between threads? Where is the data to be stored? 3. What operations on data are needed for each thread? Where should this logic be stored? 4. Where will data be accessed concurrently from different threads, i.e. where do you need to provide mutual exclusion? 5. Are there other situations in the alarm clock where semaphores are needed for synchronization? Hint: study the ClockInput class. 6. If you in a thread wait for the next second by simply calling sleep(1000), what will the effect on the clock time be? Is this ok for alarm clock time updating? Can it be improved? Specification 1. The displayed clock time should be updated every second (by calling the ClockOutput.showTime method). Note: when the user has selected set alarm or set time, the hardware/emulator shows the set time and an update of the clock time will have no effect on the clock display. Still, the clock time should be updated every second regardless of mode. 2. It should be possible to set the clock time and the alarm time. The hardware/emulator internally handles the actual setting/editing of the time value. When the user selects another mode, the set value is written to the ClockInput object and give is called for its semaphore. For example, the user selects set alarm and edits (using number keys or arrows) the alarm time. Nothing needs to be done by the control software. Then the user selects set time and the alarm time is written to the ClockInput 103
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JAVA-BASED REAL-TIME PROGRAMMING Kl
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• Each piece of software must be
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Contents I Concurrent programming i
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Part I Concurrent programming in Ja
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1. Introduction pany depends on the
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1. Introduction control may be dela
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Chapter 2 Fundamentals Goal: Review
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2.2. Our physical world is parallel
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2.4. Concurrency a trend that the p
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2.4. Concurrency Behind the term co
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2.4. Concurrency in functions like
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2.5. Interrupts, pre-emption, and r
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2.5. Interrupts, pre-emption, and r
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2.6. Models of concurrent execution
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Object properties Implicit mutual e
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2.6. Models of concurrent execution
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2.7 Multi-process programming 2.7.
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2.9. Software issues In this chapte
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Chapter 3 Multi-Threaded Programmin
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3.1.1 Thread creation At start of a
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to foresee the value actually retur
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3.1. Threads first obtains the curr
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the run-time system (that is, the s
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JAVA-BASED REAL-TIME PROGRAMMING

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