OperatingSystem-Homework 2 Solved

Part I (50%)
1.   (10%) Consider a computer that does not have a TEST AND SET LOCK instruction but does have an instruction to swap the contents of a register and a memory word in a single indivisible action. Can that be used to write a routine enter region such as the one found in Fig. 2–12.

2.   (20%) Measurements of a certain system have shown that the average process runs for a time T before blocking on I/O. A process switch requires a time S, which is effectively wasted (overhead). For roundrobin scheduling with quantum Q, give a formula for the CPU efficiency (i.e., the useful CPU time divided by the total CPU time) for each of the following:

(a)    Q=∞

(b)    Q>T

(c)    S<Q<T

(d)    Q=S

(e)    Q nearly 0

3.   (10%) Consider the interprocess-communication scheme where mailboxes are used. Suppose a process P wants to wait for two messages, one from mailbox A and one from mailbox B. What sequence of send and receive should it execute so that the messages can be received in any order?

4.   (10%) Consider the following program that uses the Pthreads API. What would be the output of the program? (Note that the line numbers are for references only.)

Listing 1: pthread.c

 

1    #include <stdio.h>

2    #include <stdlib.h>

3    #include <unistd.h>

4    #include <pthread.h>

5    #include <sys/types.h>

6

7 int value = 1;

8

9 static void *runner(void *param);

10

11                                                int main(int argc, char **argv)

12                                                {

13                                                pid_t pid = fork();

14                                                if (pid > 0) {

15                                                printf("A = %d\n", value);

16                                                }

17                                                else if (pid == 0) {

18                                                pid_t pid = fork();

19                                                if (pid > 0) {

20                                                printf("B = %d\n", value);

21                                                }

22                                                else if (pid == 0) {

23                                                pid_t pid = fork();

24                                                pthread_t tid;

25                                                pthread_attr_t attr;

26                                                pthread_attr_init(&attr);

27                                                pthread_create(&tid, &attr, runner, NULL);

28                                                pthread_join(tid, NULL);

29                                                if (pid > 0)

30                                                printf("C = %d\n", value);

31                                                else

32                                                printf("D = %d\n", value);

33                                                }

34                                                else {

35                                                exit(1);

36                                                }

37                                                }

38                                                else {

39                                                exit(1);

40                                                }

41

42               return 0;

43               }

44

45               static void *runner(void *param)

46               {

47               value += 1;

48               pthread_exit(0);

49               }
 

Part II (50%)
Write a program to simulate the dining philosopher problem mentioned in the textbook using the Pthreads API on Linux. Make sure that your implementation is able to handle 5 philosophers and is free of race condition.