JAVA-BASED REAL-TIME PROGRAMMING

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5. Solutions 5.4 Solution to exercise 6 Scheduling a) The CPU-load due to the threads A, B, and C is 1/4+2/5+1/8 = 31/40 = 0.775 = 77.5 When making such a schedule, we utilize that the worst case is when all threads are released at the same time. Here we use rate-monotonic scheduling (RMS) which means that shortest T runs first and so on. An actual schedule (see top three lines in the scheduling figure) then shows (as we already know) that the system is schedulable., and the worst-case response time R will be A: 1, B: 3, C: 4. b) As the ABCD-part of the sheduling figure shows, the system is schedulable even with the thread D which gets the response time 14 time units. c) The system ABCE is not possible to schedule because E cannot complete until t=13.2 which is past the deadline. Hence, not schedulable. 148 2012-08-29 16:05
Scheduling with blocking a) We obtain the following maximum blocking times: A: max([M1:b+M2:t], [M1:c]) = [M1:b+M2:t] = 1.0+0.5 = 1.5 B: max([M2:t via A,C], [M1:c]) + [M3:y] = 0.5+2.0 = 2.5 C: [M3:y via B,D] = 2.0 5.4. Solution to exercise 6 Note that D will never be blocked since it does not share any resources with any lower priority thread. Further note that even if C does not directly share any resources with any lower priority thread, it can still be delayed by the time of the y operation; assume D has just entered y and C is preempted by B which will be blocked by D’s call of y. We obtain a nominal maximum response time by adding the blocking times to the response time according to exercise 2. But additionally, higher priority threads might be scheduled to run again (possibly several times) within the nominal response time. Therefore, we iteratively have to add an appropriate (according the constructed schedule) number of execution time for additional invocations of higher priority threads. Hence: Where R0 denotes the response time without blocking, L denotes the worst case blocking time, and R denotes the worst-case response time we are trying to compute. Note that since the response time of thread B (in the first iteration) gets longer than the period of thread A, A will run a second time before B can complete its execution. Also note that when A executes the second time, it cannot be blocked by C since B is running, and it does not matter if A should be blocked by B since that is the thread we analyze. The maximum response time for B is 6.5 which is above the limit 5.0. Thus, we cannot ensure that the deadline is met. Also C will not meet its deadline; the indirect blocking of 2 and the execution times will cause A to be invoked twice and B once in addition to their initial cycles. This gives the response time 10 which is too long. 149
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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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RTEvent post(RTEvent e) final void
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3.4. Message-based communication -
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