| 1 | # Rick van der Zwet
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| 2 | # StudentID: 0433373
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| 3 | # $Id: lecture7.txt 380 2007-12-14 19:15:01Z rick $
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| 4 |
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| 5 | All quotes are based on the 8th edition of Concepts of programming
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| 6 | languages from Robert W. Sebesta
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| 7 |
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| 8 | *** Chapter 13 Questions ***
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| 9 | Problem Set 3, 5, 6, 9
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| 10 |
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| 11 | 3)
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| 12 | Q: Busy waiting is a method whereby a task waits for a given event by
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| 13 | continuously checking for that event to occur. What is the main problem
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| 14 | with this approach?
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| 15 | A: Deadlocks could occurs, where all processes are waiting on each-other
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| 16 |
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| 17 | 5)
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| 18 | Q: From a book on assembly language programming for a computer that uses
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| 19 | an Intel Pentium processor determine what instructions are provided to
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| 20 | support the construction of semaphores?
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| 21 | A: According to http://jsimlo.sk/docs/cpu/index.php/lock.html, Intel
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| 22 | processors uses for example F0 (LOCK) to create lock signal or the XCHG
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| 23 | which automatically includes/sets the lock signal
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| 24 |
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| 25 | 6)
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| 26 | Q: Suppose two tasks A and B must use the shared variable Buf_Size. Task
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| 27 | A adds 2 to Buf_Size and task B subtracts 1 from it. Assume that such
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| 28 | arithmetic operations are done by the three-step process of fetching the
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| 29 | current value, performing the arithmetic, and putting the new value back.
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| 30 | In the absence of competition synchronization, what sequences of events
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| 31 | are possible and what values result from these operations? Assume the
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| 32 | initial value of Buf_Size is 6?
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| 33 | A: We use the symantic of <task>R(ead), <task>O(peration), <task>W(rite)
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| 34 | Peforming the operation is no problem and will not lead to problems if
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| 35 | execuded before a read or write;
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| 36 | * AR - AW - BR - BW = 7
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| 37 | * AR - BR - AW - BW = 5
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| 38 | * AR - BR - BW - AW = 8
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| 39 | * BR - AR - AW - BW = 8
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| 40 | * BR - AR - BW - AW = 5
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| 41 | * BR - BW - AR - AW = 7
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| 42 |
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| 43 | 9)
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| 44 | Q: What happens if a monitor procedure calls another procedure in the
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| 45 | same monitor?
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| 46 | A: The first procedure (A) will suspend till the second (B) is ready,
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| 47 | both A and B do have access to the same dataspace.
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| 48 |
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| 49 |
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