DiningPhilosophers.c

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

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

sem_t mutex;
sem_t S[N];

void * phil(void *num);
void fork_pick(int);
void fork_put(int);
void check(int);

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

int main()
{
    int i;
    pthread_t thread_id[N];
    sem_init(&mutex, 0, 1);
    system("tput reset");
    for (i = 0; i < N; i++) sem_init(&S[i], 0, 0);
    printf("Init\n");
    for (i = 0; i < N; i++) {
        printf("P%d - Thinking\n", i+1);
        pthread_create(&thread_id[i], NULL, phil, &phil_num[i]);
    }
    printf("-----\n");
    for (i = 0; i < N; i++) pthread_join(thread_id[i], NULL);
}

void *phil(void *num)
{
    int n = 1;
    while(n < 2) {
        int *i = num;
        sleep(1);
        fork_pick(*i);
        sleep(0);
        fork_put(*i);
        n++; // Uncomment to stop infinite loop
    }
}

void fork_pick(int ph_num)
{
    sem_wait(&mutex);
    state[ph_num] = HUNGRY;
    printf("P%d - Hungry\n-----\n", ph_num + 1);
    check(ph_num);
    sem_post(&mutex);
    sem_wait(&S[ph_num]);
    sleep(1);
}

void check(int ph_num)
{
    if (state[ph_num] == HUNGRY && state[LEFT] != EATING && state[RIGHT] != EATING) {
        state[ph_num] = EATING;
        sleep(2);
        printf("P%d - Picks forks %d and %d\n", ph_num + 1, LEFT + 1, ph_num + 1);
        printf("P%d - Eating\n-----\n", ph_num + 1);
        sem_post(&S[ph_num]);
    }
}

void fork_put(int ph_num)
{
    sem_wait(&mutex);
    state[ph_num] = THINKING;
    printf("P%d - Releases forks %d and %d\n", ph_num + 1, LEFT + 1, ph_num + 1);
    printf("P%d - Thinking\n-----\n", ph_num + 1);
    check(LEFT);
    check(RIGHT);
    sem_post(&mutex);
}