os_lab5

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

#define N 5 // number of philosophers

sem_t forks[N]; // one semaphore for each fork
sem_t sem; // counting semaphore for limiting the number of philosophers eating at the same time

void *philosopher(void *arg)
{
    int index = *(int*)arg;
    int meals = 0;
    while (meals < 10) {
        // thinking
        printf("Philosopher %d is thinking.\n", index);

        // get forks
        sem_wait(&sem);
        sem_wait(&forks[index]);
        sem_wait(&forks[(index + 1) % N]);

        // eating
        meals++;
        printf("Philosopher %d is eating (%dth meal).\n", index, meals);
        usleep(rand() % 1000000); // wait for a random amount of time

        // release forks
        sem_post(&forks[index]);
        sem_post(&forks[(index + 1) % N]);
        sem_post(&sem);
    }
    return NULL;
}

int main()
{
    // initialize semaphores
    sem_init(&sem, 0, N-1);
    for (int i = 0; i < N; i++) {
        sem_init(&forks[i], 0, 1);
    }

    // create threads for each philosopher
    pthread_t threads[N];
    int indices[N];
    for (int i = 0; i < N; i++) {
        indices[i] = i;
        pthread_create(&threads[i], NULL, philosopher, &indices[i]);
    }

    // wait for threads to finish
    for (int i = 0; i < N; i++) {
        pthread_join(threads[i], NULL);
    }

    // destroy semaphores
    sem_destroy(&sem);
    for (int i = 0; i < N; i++) {
        sem_destroy(&forks[i]);
    }

    return 0;
}