Question

example_thread.c

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

int shared= 0;
void race(void);

int main(){
    pthread_t player1, player2, player3;

    pthread_create(&player1, NULL, (void *)race, NULL);
    pthread_create(&player2, NULL, (void *)race, NULL);
    pthread_create(&player3, NULL, (void *)race, NULL);

    pthread_join(player1, NULL);
    pthread_join(player2, NULL);
    pthread_join(player3, NULL);
    printf("Total Number = %d\n", shared);
    return 0;

}

void race(void) {
    long i,tmp;
    for(i=1; i<=200000; i++) {
        tmp = shared;
        tmp = tmp + 1;
        shared = tmp;
    }
}

1. Use both Mutex lock and Semaphore to address the racing problem in the following program (example_thread.c). Please make sure that your output is always equal to 600000.

2.  Use your Semaphore program to generate an example with deadlock problem.

Answer 1

1)MUTEX LOCK AND SEMAPHORE TO ADDRESS THE RACING PROBLEM

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

int shared= 0;
void race(void);

int main(){
    pthread_t player1, player2, player3;

    pthread_create(&player1, NULL, (void *)race, NULL);
    pthread_create(&player2, NULL, (void *)race, NULL);
    pthread_create(&player3, NULL, (void *)race, NULL);

    pthread_join(player1, NULL);
    pthread_join(player2, NULL);
    pthread_join(player3, NULL);
    printf("Total Number = %d\n", shared);
    return 0;

}

void race(void) {
    long i,tmp;
    for(i=1; i<=600000; i++) {
        tmp = shared;
        tmp = tmp + 1;
        shared = tmp;
    }
}

2)SEMAPHORE PROGRAM TO GENERATE AN EXAMPLE WITH DEADLOCK PROGRAM

#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
#include "sections.h"
#include "mdat.h"

// TODO: Declare shared variables here
int numPhils;
sem_t * sem_arr;

void sectionInitGlobals(int numPhilosophers)
{
// TODO: Complete this function
int i;

char char_arr[50];

sem_t arr[numPhilosophers];

numPhils = numPhilosophers;

for(i = 0; i < numPhilosophers; i++)
{
sprintf(char_arr,"%d", i);
mdat_sem_init(char_arr, &arr[i], 0, 0);
}

sem_arr = arr;
}

void sectionRunPhilosopher(int philosopherID, int numRounds)
{
int lChopstick = philosopherID;
int rChopstick;

int left;
int right;

int i;
int hasEaten;
int hasLeft;
int hasRight;

if(philosopherID == 0)
rChopstick = numPhils - 1;
else
rChopstick = philosopherID - 1;

for(i = 0; i < numRounds; i++)
{
hasEaten = 0;
hasLeft = 0;
hasRight = 0;

while(hasEaten == 0)
{
sem_getvalue(&sem_arr[lChopstick], &left);
if(left >= 0 || hasLeft == 1)
{
hasLeft = 1;
}
else
{
mdat_sem_wait(&sem_arr[lChopstick]);
}

sem_getvalue(&sem_arr[rChopstick], &right);
if(right >= 0 && hasLeft != 0)
{
hasRight = 1;
}
else
{
mdat_sem_wait(&sem_arr[rChopstick]);
}

if(hasLeft != 0 && hasRight != 0)
{
eat();
hasEaten = 1;
mdat_sem_post(&sem_arr[lChopstick]);
mdat_sem_post(&sem_arr[rChopstick]);
}
}

think();
}
}