JAVA-BASED REAL-TIME PROGRAMMING

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1. Introduction control may be delayed due to the dynamics of the other part. Furthermore, assume it should be simple (no reprogramming, only altering a data value) to change the sampling period of the temperature control. A better way is to write two pieces of program, for instance two classes that handle the two control tasks. How should that be done, and what requirements does that put on the programming and run-time system? Example 2: Bank-account transactions A familiar example of concurrently occurring actions on the same data item, is bank account transactions. Assume that there are two transactions that are to be carried out at about the same time. One of them, which we call A, consists of taking out $1000 from the account via a money machine. The other transaction, which we call B, is to add a salary of $10000 to the account. Depending on the actual timing, and depending on how the bank computer performs the transactions, we obtain different cases. If one transaction is performed before the other, we have one of the two cases shown in Figure 1.2. Each sequence of operations expresses the way the computer at the bank performs the requested transactions. According to proper software engineering practice, the two sequences are preferably expressed separately as described in the previous example. Furthermore, assume that the run-time system of our computer is capable of interleaving the two sequences in such a way that they appear to be done simultaneously. Since the interleaving is not specified in the individual programs as shown in the figure, it could result in any order of operations depending on the underlying system, and it could possibly be different from time to time. For instance, we may for the above transactions obtain interleavings according to Figure 1.3. Even if automatic interleaving of code sequences often is desired to handle several tasks in parallel, we see that we must be able to specify a sequence of operations to be performed without being interrupted by other sequences manipulating the same (shared) data. We shall learn several ways to solve this type of problem. // Case 1: Withdraw first A: Read 5000 A: Amount = 5000 - 1000 A: Write 4000 B: Read 4000 B: Amount = 4000 + 10000 B: Write 14000 // Case 2: Salary first B: Read 5000 B: Amount = 5000 + 10000 B: Write 15000 A: Read 15000 A: Amount = 15000 - 1000 A: Write 14000 Figure 1.2: Two bank account transactions done in two different orders. In both cases, the original amount was 5000 and the resulting amount is 14000 as expected. 14 2012-08-29 16:05
Timing 2: A: Read 5000 B: Read 5000 A: Amount = 5000 - 1000 B: Amount = 5000 + 10000 A: Write 4000 B: Write 15000 // Timing 2: A: Read 5000 B: Read 5000 B: Amount = 5000 + 10000 B: Write 15000 A: Amount = 5000 - 1000 A: Write 4000 Figure 1.3: Execution of the two bank account transactions interleaved in two different ways. With the Timing 1, the resulting amount is 15000, but the result happens to be 4000 in the second case. Hence, the final results are wrong and vary from time to time, which is clearly not acceptable. Book outline In the next chapter, we will go though the fundamentals of program execution with special interest in the concurrency issue and in the properties of the Java language. In Chapter 3, the Java language is used for solving concurrent programming problems. Doing that, however, also reveals some deficiencies of the standard Java platform and classes. Therefore, in Chapter 4, additional classes supporting real-time programming will be presented. Then in Chapter 5, we will learn how to do real-time programming using the classes from Chapter 4. 15
Page 1: JAVA-BASED REAL-TIME PROGRAMMING Kl
Page 4 and 5: • Each piece of software must be
Page 7 and 8: Contents I Concurrent programming i
Page 9: Part I Concurrent programming in Ja
Page 12 and 13: 1. Introduction pany depends on the
Page 17 and 18: Chapter 2 Fundamentals Goal: Review
Page 19 and 20: 2.2. Our physical world is parallel
Page 21 and 22: 2.4. Concurrency a trend that the p
Page 23 and 24: 2.4. Concurrency Behind the term co
Page 25 and 26: 2.4. Concurrency in functions like
Page 27 and 28: 2.5. Interrupts, pre-emption, and r
Page 29 and 30: 2.5. Interrupts, pre-emption, and r
Page 31 and 32: 2.6. Models of concurrent execution
Page 33 and 34: Object properties Implicit mutual e
Page 35 and 36: 2.6. Models of concurrent execution
Page 37 and 38: 2.7 Multi-process programming 2.7.
Page 39 and 40: 2.9. Software issues In this chapte
Page 41 and 42: Chapter 3 Multi-Threaded Programmin
Page 43 and 44: 3.1.1 Thread creation At start of a
Page 45 and 46: to foresee the value actually retur
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Page 51 and 52: 3.1.6 Thread interruption and termi
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3.2. Resources and mutual exclusion
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class Account { int balance; Semaph
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3.3. Objects providing mutual exclu
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class Producer extends Thread { pub
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3.4 Message-based communication - M
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3.4.2 Events and buffers 3.4. Messa
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Real-Time Events - RTEvent 3.4. Mes
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3.4. Message-based communication -
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RTEvent post(RTEvent e) final void
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4. Exercises and Labs 4. In the pro
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4. Exercises and Labs /** * The buf
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4. Exercises and Labs object and gi
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4. Exercises and Labs Excerpt from
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4. Exercises and Labs 4.3 Lab 1 - A
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4. Exercises and Labs Some advice o
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4. Exercises and Labs 4.4 Exercise
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4. Exercises and Labs • CustomerH
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4. Exercises and Labs 4.5 Exercise
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4. Exercises and Labs Lab 2 prepara
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4. Exercises and Labs } /** Draws a
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4. Exercises and Labs public static
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4. Exercises and Labs Specification
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4. Exercises and Labs /** * Turns t
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4. Exercises and Labs your washing
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4. Exercises and Labs } } super(mac
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4. Exercises and Labs } /** * @retu
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4. Exercises and Labs PeriodicThrea
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4. Exercises and Labs Miscellaneous
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4. Exercises and Labs Scheduling wi
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4. Exercises and Labs Getting appro
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5. Solutions 2. With some additiona
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5. Solutions 5.2 Solution to exerci
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5. Solutions class YourMonitor { pr
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5. Solutions 5.4 Solution to exerci
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5. Solutions b) After the rewriting
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