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CPSC Name:_______________________________ 331 Exam #1 Review September 24, 2007 Write your answers in the space provided. There is one scratch page at the back of the exam. Use additional sheets if you need more room. Put your name on any additional sheets that you use. Note: questions are printed on both sides of the page. If you don't know how to complete a problem, explain as much as you can about your approach. Showing your approach can earn you some extra credit. There are 6 questions worth a total of 100 points and 1 extra credit question worth a total of 10 points. The table below lists all of the questions with their respective points. The score column will be used during grading; do not write in this box. Question 1 2 3 4 5 6 7 (EC) Total Total 30 10 15 15 15 15 10 100 Score 1. [30 points] For the following, write true if the statement is true or write false if the statement is false. In a few sentences, justify your answer. (a) One function of the OS is to provide an extended machine, which it does by supplying additional userfriendly hardware. (b) A process is also known as a lightweight thread. (c) A monitor can be simulated using semaphores. (d) Deadlock is when one or more processes (or threads) are prevented from making forward progress. (e) Running the kill command with the -f option kills the process even if the process is in a defunct state. (f) A critical section is a region of code that must be executed in parallel with other processes (or threads). (g) A shell program runs user-speci ed commands in separate threads. (h) A context switch occurs when switching scheduling algorithms. (i) A le system does not always form a perfect tree. (j) Disabling interrupts is not an acceptable approach for providing mutual exclusion. 2. [10 points] Describe multiprogramming timesharing. and What are the differences between each? In what kinds of systems are these used and in what kinds of systems are they not used? 3. [15 points] How does the operating system manage processes in a timesharing system? What data structures does it use and what information does it need to keep track of? What are the implications of the data structures on performance? 4. [15 points] How does Peterson s approach to mutual exclusion work? Write some pseudocode illustrating his approach. Is Peterson s approach commonly-used to provide mutual exclusion? Why or why not? 5. [15 points] Describe a semaphore, mutex, monitor, and test-and-set lock. Are these interchangeable, i.e., can we one to simulate the other three? 6. [15 points] In the code below, which solves the dining philosophy problem, is it strictly necessary to set the state variable to HUNGRY in the procedure take_forks? In addition, could we swap the assignment to HUNGRY with the call to test? void philosopher(int i) { while (TRUE) { think(); take_forks(i); eat(); put_forks(i); } } void put_forks(int i) { down(&mutex); state[i] = THINKING; test(LEFT); test(RIGHT); up(&mutex); } void take_forks(int i) { down(&mutex); state[i] = HUNGRY; test(i); up(&mutex); down(&s[i]); } void test(int i) { if (state[i] == HUNGRY && state[LEFT] != EATING && state[RIGHT] != EATING) { state[i] = EATING; up(&s[i]); } } Extra Credit 7. [10 points] Describe some features of modern processors that add complexity to the operating system designer. Make sure you explain why these features cause complexity for the OS designer. Scratch Page

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