Q 1. (10 Points) Assume that a process executes the following pseudo codes:

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1 CS630: Operating System Design Second Exam, Spring 2014 Q 1. (10 Points) Assume that a process executes the following pseudo codes: #4 #5 #6 #7 #10 main (int argc, char *argv[ ]) { int I, *input; n = argc 1; input = (int *)malloc (n); for (i=0; i < n; i++) input[i] = atoi (argv[i+1]); statement_block_1; for (i=0; i < n; i++) { statement_block_2; if (input[i]%2 == 0) continue; /* last instruction */ If (!fork()) execv(); /* first instruction */ statement_block_3; sub (input[i]%3); /* last instruction */ statement_block_4; sub (int n) { statement_block_5; if (n > 1) sub (n 1); /* last instruction */ Assume that this program is executed as pseudo , find the page reference string. Note that system calls malloc() allocates dynamic memory space, atoi() converts a string to an integer, and the expression (a%b) returns the reminder of a/b. Show related work to claim credits. Q 2. (10 Points) Assume that R1 has only one instance, both R2 and R3 have two instances and a resource allocation graph is given as the following: {P1 R1, P2 R3, P3 R2, R1 P2, R2 P2, R3 P1, R3 P3. Does this system contain deadlock? Show your reasoning. If the answer is No then can we create a deadlock situation and how? Q 3. (20 Points) Given a page reference string as: {1, 3, 2, 4, 1, 3, 5, 1, 3, 2, 4, 5. Does this page reference string suffer from Belady s anomaly when the page replacement algorithm is a) FIFO, and b) LRU? Note: you will need to check the window size from 3 up to 5. Q 4. (15 Points) In the code below, four processes are competing for four resources labeled A to D where get() is same as wait() and release() is the same as signal(). a) Using a RAG (resource allocation graph, show the possibility of a deadlock in this implementation. b) Modify the order of some of the get requests to prevent the possibility of any deadlock. You cannot move requests across programs, only change the order inside each program. Use a RAG to justify your answer.

2 Q 5. (45 Points) Consider the Demand Paging problem. P A and P B are two programs in a file system. Assume that a page reference string is made by recording the virtual page number every 2 ticks as the process is executing. When P A is executed, the page reference string will be given as: {4, 5, 6, 10, 10, 5, 6, 10, 7, and when P B is executed, the page reference string will be given as: {4, 4, 4, 5, 5. Assume that there are two processes in the system just before t=0: P 1 executes P A and P 2 executes P B. For P A, assume that the first instruction in page#10 fork a new process which executing P B. Assume that each page fault needs 4 ticks to be handled, and page faults are handled on a first-come-first-serve fashion. Draw a Gantt chart to illustrate the scheduling of these processes and their child processes and to find the number of page faults for each process if a round-robin, non-preemptive scheduling with a time quantum of 4 ticks is used. Assume that the working set contains 3 pages and uses the FIFO page replacement method. Show your work. CS630: Operating System Design Second Exam, Fall 2013 Q 1. (35 Points) Assume that PA and PB are distinguishing programs in the file system. Assume that a page reference string is made by recording the virtual page number every 2 ticks as the process is executing. When PA is executed it starts at page 4, and then it executes pages {5, 6 if the input data is an odd number otherwise it executes pages {5, 21, 22; and the input data is given by online arguments. After the input data are processed it executing pages {7, 8 before it exits. Assume that the first instruction in page #5 is going to forks a new process which executing PB and the last instruction in page #21 is to do a disk I/O. On the other hand, PB is straight forward to execute pages {4, 4, 4, 5, 6. Assume that there are two processes in the system just before t=0: P 1 it is executed as PA and P 2 is executed as PA 2 4. Assume that the I/O controller needs 3 ticks to handle each I/O request, and I/O requests are handled on a first-come-first-serve basis. Draw a Gantt chart to illustrate the scheduling of these processes and to find the number of page faults for each process if a roundrobin, non-preemptive scheduling with a time quantum of 4 ticks is used. Note that you do not need to consider page replacement for this question.

3 Q 2. (15 Points) In the code below, three processes are competing for six resources labeled A to E where get() is same as wait() and release() is the same as signal(). c) Using a RAG (resource allocation graph, show the possibility of a deadlock in this implementation. d) Modify the order of some of the get requests to prevent the possibility of any deadlock. You cannot move requests across programs, only change the order inside each program. Use a RAG to justify your answer. Q 3. (35 Points) Assume that P A, P B and P C are three distinguish programs in a file system. Assume that a page reference string is made by recording the virtual page number every 2 ticks as a process is executing. When P A is executed, the page reference string will be made as: {4, 5, 6, 10, 10, 5, 6, 10, 7 where the first instruction in page #6 forks a new process which executing P B. Assume that when P B is executed, the page reference string shown below is recorded: {5, 5, 6, 6, 6, 7 where the first instruction in page #6 for P B forks a new process which executing P C. Assume that when P C is executed, the page reference string shown below is recorded: {4, 4, 4, 5, 5. Assume that there are two processes in the system just before t=0: P 1 executes P A and P 2 executes P B. Assume that the OS needs 4 ticks to handle each page fault, and page faults are handled on a first-come-first-serve fashion. Draw a Gantt chart to illustrate the scheduling of all the processes created and to find the number of page faults for each process if a round-robin non-preemptive scheduling with a time quantum of 4 ticks is used. Assume that the working set contains 3 frames and uses the FIFO page replacement method. Show your work.

4 Q 4. (15 Points) Consider a system with a total of 150 units of buffers, allocated to three processes as shown: Apply the banker s algorithm to determine whether it would be safe to grant each of the following requests. If yes, indicate a safe sequence that could be guaranteed possible. If no, indicate the reduction of the resulting allocation table. a) A fourth process arrives, with a maximum need of 60 and an initial need of 25 units. b) A fourth process arrives, with a maximum need of 60 and an initial need of 35 units. Problem 1. CS630: Operating System Design Second Exam, Spring 2013 Assume that a process executes the following pseudo codes: #4 #5 #6 #7 #10 main (int argc, char *argv[ ]) { int I, *input; n = argc 1; input = (int *)malloc (n); for (i=0; i < n; i++) input[i] = atoi (argv[i+1]); statement_block_1; for (i=0; i < n; i++) { statement_block_2; if (input[i]%2 == 0) continue; /* last instruction */ statement_block_3; if (input[i]%3!= 0) sub (input[i]%3); /* last instruction */ statement_block_4; sub (int n) { statement_block_5; if (n > 1) sub (n 1); /* last instruction */ Assume that this program is executed as PA , find the page reference string. Note that system calls malloc() allocates dynamic memory space, atoi() converts a string to an integer, and the expression (a%b) returns the reminder of a/b. Show related work to claim credits. (10 Points)

5 Problem 2. Consider the Demand Paging problem. P A and P B are two programs in a file system. Assume that a page reference string is made by recording the virtual page number every 2 ticks as the process is executing. When P A is executed, the page reference string will be given by the output of Problem #1. Assume that when P B is executed, the page reference string shown below is recorded: {4, 4, 4, 5, 5. Assume that there are two processes in the system just before t=0: P 1 executes P A and P 2 executes P B. If you have problem to use the result from Problem #1, then use the following page reference string with a penalty: {4, 5, 6, 10, 10, 5, 6, 10, 7. Assume that the first instruction both in page #6 and #10 fork a new process which executing P B. Assume that the OS needs 4 ticks to handle each page fault, and page faults are handled on a first-come-first-serve fashion. Draw a Gantt chart to illustrate the scheduling of these processes and their child processes and to find the number of page faults for each process if a RR, non-preemptive scheduling with a time quantum of 4 ticks is used. Assume that the working set contains 3 pages and uses the FIFO page replacement method. Show your work. (45 Points) Problem 3. Deadlock: A system that uses the Banker's Algorithm deadlock avoidance has five processes (P1, P2, P3, P4, and P5) and four types of resources and each has multiple instances (13 of A, 13 of B, 9 of C, and 13 of D). Is the following state safe or not? If it is, show the safe sequence. If not, show how they can deadlock. (20 Points) Process Max Allocation P P P P P Problem 4. Assume a disk with 200 tracks and that the disk request queue has random requests in it. The requested tracks, in the order received are: 55, 58, 39, 18, 90, 160, 150, 38, and 184. Assuming that the read/write head is currently located at track 100 and it is moving toward track 200. Show the sequence that the requests will be serviced and the total track sequence traversed for each of the following scheduling policies: FCFS, SCAN and C-LOOK. (10 Points) Problem 4. a) Three processes share four resource units that can be reserved and released only one at a time. Each process needs a maximum of two units. Show that a deadlock cannot occur. (10 Points) b) Evaluate the Banker s algorithm for its usefulness in real life. Give at least two reasons to justify your choice. (5 Points)