Question

Dining Philosopher problem solution- Vulnerable to starvation in c language or either java - using threads(can use semaphores but with threads) - with proper explanations and comments Please provide output of program and explanation of how to run program.

Answer 1

file name dinning.c

#include <pthread.h>
#include <unistd.h>
#include <semaphore.h>
#include <stdio.h>

#define N 5
#define THINKING 2
#define HUNGRY 1
#define EATING 0
#define LEFT (phnum + 4) % N
#define RIGHT (phnum + 1) % N

int state[N];
int phil[N] = { 0, 1, 2, 3, 4 };

sem_t mutex;
sem_t S[N];

void test(int phnum)
{
   if (state[phnum] == HUNGRY
       && state[LEFT] != EATING
       && state[RIGHT] != EATING) {
       // state that eating
       state[phnum] = EATING;

       sleep(2);

       printf("Philosopher %d takes fork %d and %d\n",
                   phnum + 1, LEFT + 1, phnum + 1);

       printf("Philosopher %d is Eating\n", phnum + 1);

       // sem_post(&S[phnum]) has no effect
       // during takefork
       // used to wake up hungry philosophers
       // during putfork
       sem_post(&S[phnum]);
   }
}

// take up chopsticks
void take_fork(int phnum)
{

   sem_wait(&mutex);

   // state that hungry
   state[phnum] = HUNGRY;

   printf("Philosopher %d is Hungry\n", phnum + 1);

   // eat if neighbours are not eating
   test(phnum);

   sem_post(&mutex);

   // if unable to eat wait to be signalled
   sem_wait(&S[phnum]);

   sleep(1);
}

// put down chopsticks
void put_fork(int phnum)
{

   sem_wait(&mutex);

   // state that thinking
   state[phnum] = THINKING;

   printf("Philosopher %d putting fork %d and %d down\n",
       phnum + 1, LEFT + 1, phnum + 1);
   printf("Philosopher %d is thinking\n", phnum + 1);

   test(LEFT);
   test(RIGHT);

   sem_post(&mutex);
}

void* philospher(void* num)
{

   while (1) {

       int* i = num;

       sleep(1);

       take_fork(*i);

       sleep(0);

       put_fork(*i);
   }
}

int main()
{

   int i;
   pthread_t thread_id[N];

   // initialize the semaphores
   sem_init(&mutex, 0, 1);

   for (i = 0; i < N; i++)

       sem_init(&S[i], 0, 0);

   for (i = 0; i < N; i++) {

       // create philosopher processes
       pthread_create(&thread_id[i], NULL,
                   philospher, &phil[i]);

       printf("Philosopher %d is thinking\n", i + 1);
   }

   for (i = 0; i < N; i++)

       pthread_join(thread_id[i], NULL);
}

to run the program use
gcc dinning.c -pthread -o din

Output

./din
Philosopher 1 is thinking
Philosopher 2 is thinking
Philosopher 3 is thinking
Philosopher 4 is thinking
Philosopher 5 is thinking
Philosopher 1 is Hungry
Philosopher 2 is Hungry
Philosopher 4 is Hungry
Philosopher 3 is Hungry
Philosopher 3 takes fork 2 and 3
Philosopher 3 is Eating
Philosopher 5 is Hungry
Philosopher 5 takes fork 4 and 5
Philosopher 5 is Eating
Philosopher 3 putting fork 2 and 3 down
Philosopher 3 is thinking
Philosopher 2 takes fork 1 and 2
Philosopher 2 is Eating
Philosopher 5 putting fork 4 and 5 down
Philosopher 5 is thinking
Philosopher 4 takes fork 3 and 4
Philosopher 4 is Eating
Philosopher 3 is Hungry
Philosopher 2 putting fork 1 and 2 down
Philosopher 2 is thinking

In this program when you create an pthread all the threads run independently, so any philosopher can take the fork and put the fork back.