midterm

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CS 471
Operating Systems

Spring 2013
Midterm Exam

Time 2 & 1/2 hours

Open Book & Notes

Name:

Unix Login:

Each Question is 25 points.

Question 1

What is the print out of the following programs:

int main()

{

fork();

printf("Norfolk\n");

fork();

printf("Virginia Beach\n");

fork();

printf("Newport News\n");

}

int main()

{

if (fork()){

printf("Hampton\n");

exit(0);

}

if (fork())

printf("Suffolk\n");

if (fork())

printf("Chesapeake\n");

}

int main()

{

if (fork()) execl("q1cexec", "q1cexec", ODU, 0);

if (fork()) execl("q1cexec", "q1cexec", UVA, 0);

if (fork()) execl("q1cexec", "q1cexec", NSU, 0);

sleep(1);

printf("Q1c cs471w\n");

}

Q1cexec:

int main(int argc, char *argv[])

{

printf("%s: q1cexec cs471w\n", argv[1]);

}

Question 2

Consider the following 3 processes submitted in the order:

P1, P2 and P3 with estimated CPU times: 9, 3, 6

Compute the average waiting time if these 3 processes are scheduled according to:

1) FCFS:

2) SJF:

3) LJF (Longest Job First)

4) RR with Quantum time = 3. How many context switches are needed?

Question 3

Complete the following code:

The parent sends A and B to the child via pipe1.

The child adds the two received values and sends the result back to the parent via pipe2.

The parent prints the results and exits.

int main(void)

{

int pipe1[2];

int pipe2[2];

int pid;

int A , B, C;

char buf[SIZE];

bzero(buf, SIZE);

pipe(pipe1);

pipe(pipe2);

pid = fork();

if (pid==0) { /* Child Code */

}

else { /* Parent Code */

srand((unsigned) time(0));

A = rand() % 100;

B = rand() % 100;

}

What is the output of the following program:

int main()

{

int segment_id = shmget(IPC_PRIVATE, sizeof(int), S_IRUSR | S_IWUSR);

int *sharedvariable = (int *) shmat(segment_id, NULL, 0);

*sharedvariable = 0;

int pid;

pid = fork();

if (pid==0) {

usleep(10);

while (1) {

printf("Child got: %d\n", *sharedvariable);

(*sharedvariable)++;

sleep(1);

}

else {

while (*sharedvariable < 10) {

(*sharedvariable)++;

sleep(1);

printf("Parent got: %d\n", *sharedvariable);

}

kill (pid, 9);

}

What is the output of the following program.

int sfd;

int main()

{

char buf[SIZE];

bzero(buf, SIZE);

int pid;

sfd = open("tmpfile", O_RDWR | O_TRUNC | O_CREAT, 0600);

int i = 0;

pid = fork();

if (pid==0) {

usleep(10);

while (1) {

lseek(sfd, 0, SEEK_SET);

read(sfd, buf, SIZE);

printf("Child got: %s\n", buf);

i = atoi(buf);

i++;

sprintf(buf, "%d", i);

lseek(sfd, 0, SEEK_SET);

write(sfd, buf, strlen(buf));

sleep(1);

}

else {

while (i < 10) {

sprintf(buf, "%d", i);

lseek(sfd, 0, SEEK_SET);

write(sfd, buf, strlen(buf));

sleep(1);

lseek(sfd, 0, SEEK_SET);

read(sfd, buf, SIZE);

printf("Parent got: %s\n", buf);

i = atoi(buf);

i++;

}

kill (pid, 9);

}

Question 4

What is the output of the following programs?

#define SA struct sockaddr

#define SIZE 10

void *Child();

void *Parent();

pthread_t thread1, thread2;

main(int argc, char *argv[])

{

pthread_create(&thread1, NULL, &Parent, NULL);

pthread_create(&thread2, NULL, &Child, NULL);

pthread_join(thread1, NULL);

exit(0);

}

void *Child()

{

int sockfd, n;

struct sockaddr_in servaddr;

struct hostent *hp, *gethostbyname();

char buf[100];

int i;

bzero(&servaddr, sizeof(servaddr));

hp = gethostbyname("localhost");

bcopy(hp->h_addr, &(servaddr.sin_addr.s_addr), hp->h_length);

servaddr.sin_family = AF_INET;

servaddr.sin_port = htons(10294);

sockfd = socket(AF_INET, SOCK_STREAM, 0);

printf("Child connecting\n");

connect(sockfd, (SA *) & servaddr, sizeof(servaddr));

printf("Child connected\n");

while (1) {

read(sockfd, buf, SIZE);

printf("Child got: %s\n", buf);

i = atoi(buf);

i++;

sprintf(buf, "%d", i);

write(sockfd, buf, strlen(buf));

sleep(1);

}

void *Parent()

{

int len, listenfd, connfd;

struct sockaddr_in servaddr, cliaddr;

char buf[512];

int i = 0;

bzero(&servaddr, sizeof(servaddr));

servaddr.sin_family = AF_INET;

servaddr.sin_addr.s_addr = htonl(INADDR_ANY);

servaddr.sin_port = htons(10294);

listenfd = socket(AF_INET, SOCK_STREAM, 0);

bind(listenfd, (SA *) & servaddr, sizeof(servaddr));

listen(listenfd, 0);

len = sizeof(cliaddr);

printf("Parent accepting\n");

connfd = accept(listenfd, (SA *) & cliaddr, &len);

printf("Parent accepted\n");

while (i < 10) {

sprintf(buf, "%d", i);

write(connfd, buf, strlen(buf));

sleep(1);

read(connfd, buf, SIZE);

printf("Parent got: %s\n", buf);

i = atoi(buf);

i++;

}

printf("Parent thread is done\n");

pthread_exit(0);

}

void *function1();

void *function2();

pthread_mutex_t mutexA = PTHREAD_MUTEX_INITIALIZER;

pthread_t thread1, thread2;

int sharedvariable = 0;

main(int argc, char *argv[])

{

pthread_create(&thread1, NULL, &function1, NULL);

pthread_create(&thread2, NULL, &function2, NULL);

pthread_join(thread2, NULL);

exit(0);

}

void *function1()

{

usleep(10);

while (1) {

pthread_mutex_lock(&mutexA);

printf("Child got: %d\n", sharedvariable);

sharedvariable++;

pthread_mutex_unlock(&mutexA);

sleep(1);

}

void *function2()

{

while (sharedvariable < 10) {

pthread_mutex_lock(&mutexA);

sharedvariable++;

printf("Parent got: %d\n", sharedvariable);

pthread_mutex_unlock(&mutexA);

sleep(1);

}

printf("Parent thread is done\n");

pthread_exit(0);

}