[SOLVED] Operating-System Homework 2

Part I

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 round- robin 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 pro- gram? (Note that the line numbers are for references only.)

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int value = 1;
static void *runner(void *param);

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

    pid_t pid = fork();
    if (pid > 0) {

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

    else if (pid == 0) {
        pid_t pid = fork();
        if (pid > 0) {

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

        else if (pid == 0) {
            pid_t pid = fork();
            pthread_t tid;
            pthread_attr_t attr;
            pthread_attr_init(&attr);
            pthread_create(&tid, &attr, runner, NULL);
            pthread_join(tid, NULL);

if(pid>0)
printf(“C = %d\n”, value);

else

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

}
else {

exit(1); }

}
else {

exit(1); }

return 0; }

static void *runner(void *param)
{

value += 1;

    pthread_exit(0);
}

Listing 1: pthread.c

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10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/types.h>

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.

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Gentle Reminder

Once again, as mentioned in the instructions, neither late nor copied homework will be accepted.

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