• İhsan Doğramacı Bilkent University

• CS 342

CS342 Operating Systems

Fall 2024

Homework #2

Assigned: Oct 23, 2024.

Due date: Nov 7, 2024. Document version: 1.0

Q1. We have the following program. What are the pairs of values printed out

by this program?

int a = 3200;

int b = 1000;

int ret;

int main()

{

ret = fork();

a = a + 50;

if (ret == 0) {

a = a * 3;

b = b + 150;

printf ("%d %d\n", a, b);

if (fork() == 0) {

a = a + 2000;

printf ("%d %d\n", a, b);

exit(0);

}

b = b + 115;

}

else {

a = a + 210;

b = 3 * b;

printf ("%d %d\n", a, b);

b = b + 90;

}

printf ("%d %d\n", a, b);

} Q

2. Consider the following program. What are the values that are printed out

by this program?

unsigned long x = 1000;

unsigned long y = 2000;

unsigned long z = 400;

void * func1(void *p)

{

unsigned long x, z;

x = 7000;

y = 4000;

z = *((unsigned long *)p);

z = z + 5000;

*((unsigned long *)p) += 500;

printf ("%lu %lu %lu\n", x, y, z);

2

pthread_exit(NULL);

}

int

main()

{

pthread_t tid;

unsigned long a = 3000;

pthread_create (&tid, NULL, &func1, (void *)&a);

pthread_join(tid, NULL);

printf ("%lu %lu %lu\n", x, y, z);

} Q

3. Consider the following program. Find out the triples printed out by this

program. What can you say about their order?

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <pthread.h>

unsigned long a=100;

unsigned long b=200;

#define COUNT 5

pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;

void * func(void *p)

{

unsigned long a = 50;

pthread_mutex_lock(&lock);

a = a + 20;

b = b + 30;

pthread_mutex_unlock(&lock);

printf ("%lu %lu %lu\n", a, b, (unsigned long)p);

pthread_exit(NULL);

}

int main()

{

pthread_t tids[COUNT];

unsigned long k;

int ret;

for (k = 0; k < COUNT; ++k)

pthread_create (&(tids[k]), NULL, &func, (void *) (k+1));

for (k = 0; k < COUNT; ++k)

pthread_join(tids[k], NULL);

printf ("%lu %lu %lu\n", a, b, k);

exit (0);

}