Dining Problem

// Hyung Jun Hahn

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

#define NUM_PERSON 5

void think(int);
void eat(int);
void pickup_forks(int);
void return_forks(int);
void *person(void *count);

pthread_mutex_t forks[NUM_PERSON];

int main() {
    pthread_t tid[NUM_PERSON];
    pthread_attr_t attr;

    srand(time(NULL));
    int i;
    for (i = 0; i < NUM_PERSON; ++i) {
        pthread_mutex_init(&forks[i], NULL);
        pthread_attr_init(&attr);
        pthread_create(&tid[i], &attr, person, (void *) i);
    }

    for (i = 0; i < NUM_PERSON; ++i) {
        pthread_join(tid[i], NULL);
    }
    return 0;
}

void *person(void *count) {
    int* num = (int *)count;
    int temp = num;
    while (1) {
        think(temp);
        pickup_forks(temp);
        eat(temp);
        return_forks(temp);
    }
}

void think(int num) {
    // 1~3 seconds
    int time = (rand() % 3) + 1;
    printf("Person(%d) thinking for %d seconds\n", num, time);
    sleep(time);
}

void eat(int num) {
    // 1~3 seconds
    int time = (rand() % 3) + 1;
    printf("Person(%d) eating for %d seconds\n", num, time);
    sleep(time);
}

void pickup_forks(int num) {
    int left = (num + NUM_PERSON) % NUM_PERSON;
    int right = (num + 1) % NUM_PERSON;

    if (num == 1) {
        printf("Person(%d) waiting to pick up fork %d\n", num, right);
        pthread_mutex_lock(&forks[right]);
        printf("Person(%d) picked up fork %d\n", num, right);
        printf("Person(%d) waiting to pick up fork %d\n", num, left);
        pthread_mutex_lock(&forks[left]);
        printf("Person(%d) picked up fork %d\n", num, left);
    } else {
        printf("Person(%d) waiting to pick up fork %d\n", num, left);
        pthread_mutex_lock(&forks[left]);
        printf("Person(%d) picked up fork %d\n", num, left);
        printf("Person(%d) waiting to pick up fork %d\n", num, right);
        pthread_mutex_lock(&forks[right]);
        printf("Person(%d) picked up fork %d\n", num, right);
    }
}

void return_forks(int num) {
    printf("Person(%d) putting down forks\n", num);
    pthread_mutex_unlock(&forks[(num + 1) % NUM_PERSON]);
    pthread_mutex_unlock(&forks[(num + NUM_PERSON) % NUM_PERSON]);
}