Question

C programming:

Using the following rules of the Dining philosophers problem:

• N philosophers spend their lives thinking and eating rice.

• There are only N chopstick on the table, one between every two philosophers.

• In order to eat, a philosopher needs to get hold of the two chopsticks that are closest to her.

• A philosopher cannot pick up a chopstick that is already taken by a neighbor.

Implement the dining philosophers problem using pthreads and monitor.

Your program should print the philosopher that is eating, the chopsticks that is using and when the philosopher finished eating.

A correct implementation will run like this:

./diningPhilo
Philosopher 0 is eating using:0,1
Philosopher 2 is eating using:2,3
Philosopher 4 is eating using:4,5
Philosopher 8 is eating using:8,9
Philosopher 6 is eating using:6,7
Philosopher 0 finished eating
Philosopher 6 finished eating
Philosopher 6 is eating using:6,7
Philosopher 2 finished eating
...

Answer 1

#include <pthread.h>
#include <semaphore.h>
#include <stdio.h>
#define THINKING 2
#define HUNGRY 1
#define EATING 0

#define LEFT (phnum+n-1)% N

#define RIGHT (phnum+1)%N

int state[N];
int phil[N];

sem_t mutex;
sem_t S[N];

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

{
       state[phnum] = EATING;

       sleep(2);

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

{

sem_wait(&mutex);

printf("philosopher %d finished eating\n",phnum);

test(phnum);

sem_post(&mutex);

sem_wait(&s[phnum]);

sleep(1);

}

void* philospher(void* num)
{

   while (1) {

       int* i = num;

       sleep(1);

       take_fork(*i);

       sleep(0);

       put_fork(*i);

sleep(1);

finish(*i);

   }
}

int main()
{

   int i;
   pthread_t thread_id[N];

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

printf("enter the total number of philosophers having in a dinning table : \n");

scanf("%d",&n);

printf("ente the id's of each philosopher: \n");

for (i=0;i<n;i++)

{

scanf("%d",&a[i]);

}

   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);
}