peterson's-sol.c

peterson's-sol.c

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

#define NUM_THREADS 2

atomic_int turn = 0;
atomic_int flag[2] = {0, 0};
int in_cs = 0;
int pin_cs[2] = {0, 0};
struct timespec ts = {.tv_nsec = 50};
pthread_t threads[NUM_THREADS];
pthread_t print_thread;

void *process(void *arg) {
    int id = *((int *)arg);
    printf("start p%d\n", id);

    while (1) {
        atomic_store(&flag[id], 1);
        atomic_thread_fence(memory_order_seq_cst);
        atomic_store(&turn, !id);

        while (atomic_load(&flag[!id]) && atomic_load(&turn) == !id)
            ;

        /* Critical Section */
        in_cs++;
        nanosleep(&ts, NULL);
        pin_cs[id]++;
        if (in_cs == 2)
            fprintf(stderr, "p0 and p1 are in the critical section\n");
        nanosleep(&ts, NULL);
        in_cs--;

        /* Remainder Section */
        atomic_store(&flag[id], 0);
    }
}

void *print_cs(void *arg) {
    while (1) {
        sleep(1);
        printf("p0: %d, p1: %d\n", pin_cs[0], pin_cs[1]);
    }
}

int main() {
    int i;
    int thread_ids[NUM_THREADS];

    for (i = 0; i < NUM_THREADS; i++) {
        thread_ids[i] = i;
        pthread_create(&threads[i], NULL, process, &thread_ids[i]);
    }

    pthread_create(&print_thread, NULL, print_cs, NULL);

    for (i = 0; i < NUM_THREADS; i++) {
        pthread_join(threads[i], NULL);
    }

    pthread_join(print_thread, NULL);

    return 0;
}