23 lines
799 B
23 lines
799 B
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Exercise 3.38: Suppose that Peter, Paul, and
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Mary share a joint bank account that initially contains $100. Concurrently,
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Peter deposits $10, Paul withdraws $20, and Mary withdraws half the money in
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the account, by executing the following commands:
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Peter: (set! balance (+ balance 10))
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Paul: (set! balance (- balance 20))
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Mary: (set! balance (- balance
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(/ balance 2)))
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List all the different possible values for balance after these three
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transactions have been completed, assuming that the banking system forces the
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three processes to run sequentially in some order.
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What are some other values that could be produced if the system allows the
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processes to be interleaved? Draw timing diagrams like the one in Figure 3.29
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to explain how these values can occur.
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