JAVA-BASED REAL-TIME PROGRAMMING

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5. Solutions 5.2 Solution to exercise 3 Buffer The getLine method is simply written symmetrical and analogous to the put- Line method. class Buffer { // Attributes and constructor ... } synchronized void putLine(String inp) { // According to exercise... } synchronized String getLine() { try { while (available ==0) wait(); } catch (InterruptedException exc) { throw new RTError("Buffer.getLine interrupted: "+exc); }; String ans = buffData[nextToGet]; buffData[nextToGet] = null; if (++nextToGet >= size) nextToGet = 0; available --; notifyAll(); return ans; } Note that: • The synchronized keyword tells the Java compiler to produce code that contain a mutex and data is unlocked when returning to the callee, even if the return is placed in the middle of the method and deeply nested in if statements, etc. • For more than one producer, or more than one consumer, we need while for the wait even if we only use notify (not notifyAll). Make sure that is understood. • With only one producer and one consumer, it would work with if...wait and notify instead of while...wait and notifyAll. But as a general rule we always write while. • We could have used our variables to test and only issued notify or notifyAll when really necessary, that is, when there are threads waiting. On the other hand, if no threads are waiting, notify is almost only a test. • To notify specifically for buffer not empty, or for buffer not full, we could have additional internal objects and use their event/condition/notification queue. That is, however, a bit complicated to accomplish in Java. In this course we keep it simple by only using notification for the object itself. 144 2012-08-29 16:05
Queue system 1. What data is needed in the monitor? 5.2. Solution to exercise 3 • counter to give a new customer a unique number, and a counter for the next customer to serve. • data to decide if the queue is empty • information about how many clerks there are and which clerks that are not busy. 2. What conditions must be fulfilled to permit the monitor operations to be performed? • customerArrived only registers a new customers and can always be completed. • clerkFree registers an available clerk and can always be completed. • getDisplayData requires at least one customer in line and a clerk must be available. 3. What events will cause the conditions to be fulfilled? • The conditions in getDisplayData will be fulfilled when a customer arrives and there is a clerk free. 4. What happens if an eager clerk pushes its button several times when the queue is empty? • The number of free clerks may only be increased when the clerk changes from busy to free and not for each button press. 5. Write the monitor! • Implementation follows: 145
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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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3.1.6 Thread interruption and termi
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• If the operation of an industri
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3.2. Resources and mutual exclusion
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give give give 3.2. Resources and m
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synch. T1 entry give take 3.2. Reso
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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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