CS Operating system Spring Final -- May 8, You have 120 min. Good Luck!

Transcription

1 Name / ID (please PRINT) Sequence #: Seat Number: CS Operating system Spring Final -- May 8, You have 120 min. Good Luck! This is a closed book/note examination. But You can use the reference card(s) given to you. This exam has 8 questions in 11 pages. Please read each question carefully and answer all the questions, which have 100 points in total. Feel free to ask questions if you have any doubts about questions. Partial credit will be given, so do not leave questions blank. You can also get 2pt bonus credit if you complete the following survey questions and the boldfaced two columns of the grading table below. Please do this after answering the questions in the exam. Thanks! Survey Questions (circle one): I took Data Structures from Korkmaz Clark Sherette Tosun other I took System Prog. from Lama Maynard other I took Computer Org. from Tian Muzahid Clark Yu other I took Application Prog. from Bylander Zhang Quarles Robinson other Question Topic Review Questions (all 1 from tk01 to tk12) Unix I/O and Special 2 files (tk05-, tk06-) Memory Management 3 (tk07-) Virtual Memory - 4 Demand Paging (tk08-) Possible Points Difficulty level of this question 1: Easiest 5: Most difficulty Student Expects to receive out of 20 /20 10 /10 15 /15 10 /10 5 Threads (tk09-) 10 /10 Student Received 6 Synchronization (tk10-) 15 /15 7 Signals (tk11-) 10 /10 8 Communications - socket prog., (tk12-) Bonus if this table is completed 10 /10 2 Total

2 1. [20 points] Answer the following questions with short explanations. You can also draw figures to better explain your reasoning if needed. a. [2pt] Explain the differences between System calls and Library function calls in C? b. [1pt] What is the purpose of using static before a variable name inside a C function? c. [2pt] Explain the difference between preemptive and non-preemptive scheduling. d. [1pt] What is the difference between binary file and text file? 2

3 e. [2pt] What is a Named Pipe (FIFO)? What advantages it has over regular (unnamed) pipe? f. [2pt] What do Dynamic loading and Dynamic linking mean? Why do we need them? g. [2pt] What does locality mean? How does it impact the performance of demand paging? h. [2pt] Explain how Light-Weight Process (LWP) approach works. 3

4 i. [2pt] Describe the following requirements for critical section (CS) solutions: Mutual Exclusion: Progress: Bounded Waiting: j. [2pt] Give the similarities and differences between signals (e.g., SIGINT) and interrupts? k. [1pt] A protocol is an agreement between two end points that want to communicate. What are the three main things that we need to specify when designing a networking protocol? 4

5 2. [10 points] Unix I/O and file operations - Special Files a. [5 points] Suppose that the file tmpdata.txt contains abcdefghijk. Suppose the following code is executed correctly without generating any errors. 1: int fd; 2: char buf[6] = ; 3: fd = open( tmpdata.txt, O_RDONLY); 4: fork( ); 5: read(fd, buf, 2); 6: read(fd, buf+2, 2); 7: printf( %d: %s, (long)getpid(), buf); i). [3pt] Explain if the following two outputs are possible or not? Why/why not? Suppose parent's pid is 7 while child's pid is 8. 7:b2ef5 8:a2cd5 7:abcd5 8:a2b45 ii). [2pt] Suppose the lines 3 and 4 are exchanged? Explain why (or why not) the above outputs are possible in this case. b. [5 points] Suppose you are given the inode structure as shown below. Assume that our inode structure has 10 direct pointers, and the data Block size is 8K bytes and pointers are 4 bytes. Write a function int num_of_data_block_di(struct inode *myinode); which counts the number of data blocks under double indirect link. Note that double indirect level might be partially filled with data blocks! So if there is no more data block or level, the corresponding pointer will contain NULL. Please take that into account! If needed, you can assume that the standard libraries are included here. int num_of_data_block_di(struct inode *myinode){ int i, j, k; int count=0; int num_blk_ptr = db si di ti 5

6 3. [15 points] Memory Management a. [5 points] Suppose that the virtual address space is 16 Mbytes, the physical memory is 128 Kbytes, and the page/frame size is 2 Kbytes. Show how to determine the following bits: i. [1pt] Number of bits for virtual address = ii. [1pt] Number of bits for physical address = iii. [1pt] Number of bits for offset (d) = iv. [1pt] Number of bits for page number (p) = v. [1pt] Number of bits for frame number (f) = b. [5 points] Suppose we use TLB in the above system with the following page table and TLB table entries. For memory address translation, suppose the TLB access time is 6 ns and the memory access time is 20 ns while the disk access time is 10 ms. initial page table Index Valid frame TLB page Frame For the logical/virtual address given in binary below, find the corresponding page number and frame number while estimating the time to access the actual data/instruction in the physical memory (suppose we always first check TLB and then check page table if the page number is not in TLB). Also give the corresponding physical memory address. The given logical/virtual address is [1pt] Page # [2pt] Access time [1pt] Frame # [1pt] Physical Address = = = = c. [5 points] Suppose you are writing a C program to translate a given logical/virtual address (LA) to a physical address (PA). You need to first find the page number (p) and offset number (d). Then get frame number (f) from page table and determine PS. For the above system (3.a), what statements would you use to find p, d and PA? Suppose LA is given. unsigned int p,d,f,pa,la=0x9f28a3; // d = p = f = page_table[p]; PA = 6

7 4. [10 points] Virtual Memory a. [5points] Consider a demand-paging system where the page fault time (including the times for looking up page, reading a page from the disk, and updating page table) is on average 30 milliseconds (ms) while the physical memory access time is 10 microsecond ( sec). Addresses are translated through a page table in main memory. So, each memory reference takes two memory accesses. Assume that 90% of the pages are in the page table while the 10% of the pages cause page fault. [Note: 1 ms = 1000 sec] Determine the effective Access Time (EAT) for the above system. b. [5points] Recall that "thrashing" means that a process is busy swapping pages in and out. Explain the reasons that may cause thrashing and how we can avoid thrashing. 7

8 5. [10 points] Threads Suppose we want a thread to get a structure containing two double values as a parameter and return another structure containing three types of values as defined below. You are asked to complete the following program in which the testthread() finds the sum of the received double values and then returns their sum along with an integer value of 2 and char value of 'p' to the main thread waiting to join. The main program simply prints out the returned values. You can ignore error checking. Assume all the necessary libraries are included. typedef struct { double x, y; } in_data_t; typedef struct { double sum; int i; char ch; } out_data_t; void *testthread(void *args) { } void main() { pthread_t tid; double d1= 3.14, d2=5.54; /* double values to be sent to the thread */ pthread_create(&tid, NULL, testthread, ); pthread_join(tid, ); printf(" Sum is %lf int is %d char is %c\n", ); } 8

9 6. [15 points] Synchronization a. [10 points] Suppose there are three threads P, Q and R. Each has some sequential code sections represented as function calls and then updates a shared variable count, as shown in the below table. Define and initialize semaphores and then solve the coordination and the critical section problems (use acquire/release or wait/signal). Assume that RS1() is executed after QS1()which is executed after PS1(), QS2() is executed after RS1() PS2() and RS2() are executed after QS2() /* Semaphores and initial Values: */ 2pt P Q R PS1(); QS1(); RS1(); 5pt PS2(); QS2(); RS2(); count = count + 3 count = count - 2 y = count + 5 3pt b. [5 points] What is a condition variable? When/why do we need it? 9

10 7. [10 points] Signals Suppose we have a program that calls a given function do_something() in an infinite loop. You are asked to modify/re-implement this program such that it can be terminated gracefully if the user presses ctrl-c at least three times (recall that pressing ctrl-c generates SIGINT)? Ignore error checking. // all the necessary libraries are included do_something() { /* implemented for you, just use it */ } 10

11 8. [10 points] Communications - implement a client-server program using TCP sockets. The client will first establish a TCP connection with the server. It then sends two integers (actually convert them to string and send two strings) and expect server to send back the sum of these numbers as a string. Upon receiving the sum, the client will print it and quit. The server always waits for connection requests is an infinite loop. Upon receiving a connection request, the server (parent process) creates a child process, which performs the tasks expected by the client. The parent process (server) will continue to wait for another client request. Make sure you close the socket descriptors that are not needed in the parent and child. When implementing client and server programs below, please focus on the key system calls and in which order to call them while using generic parameters (e.g., IPaddress, portnum) rather than actual structures. Also ignore error checking and assume all the necessary libraries are included. /* server.c */ int serverip = ; int serverport = 2017; void main(){ int welcomesocket, connsocket; int num1, num2, sum; char buff[10]; /* client.c */ int serverip = ; int serverport = 2017; void main() { int clientsocket; int num1=234, num2=5431, sum; char buff[10]; 11